Biology 202 Exam 4 with X2

A rare autosomal-recessive allele inherited in a Mendelian manner causes the disease cystic fibrosis. A phenotypically normal man whose father had cystic fibrosis marries a phenotypically normal woman from outside the family, and the couple consider having a family. If the frequency in the population is incredibly rare and we assume the chance of members outside of the family carrying the allele to be essentially zero, what is the probability that this couple could have affected children?

0

What symbol indicates a WT allele?

+ (+ indicates a wild-type allele, whether or not it is dominant or recessive to a mutant allele.)

What proportion of individuals from a cross between A/a; B/B; C/c; d/d; E/e and A/a; b/b; C/c; D/D; E/e will be pure breeding?

0

RF < 50%:

2 genes are linked and they are really close together on the same chromosome

Rules for x-linked recessive disorders

1) rare 2) males affected more frequently 3) skips generations 4) unaffected individuals have affected children 5) never have father to son transmission since it is x-linked 6) an affected mother gives it to all of her sons

Characteristics of autosomal dominant disorders

1) rare and often unusual to see homozygous dominant individuals 2) male and females equally affected 3) affected individuals have to have an affected parent 4) do not skip generations

Rules for autosomal recessive diseases:

1) recessive traits typically skip generations 2) recessive autosomal traits appear equally in both sexes 3) they are rare, so we assume that anyone marrying into the family isn't a carrier 4) unaffected parents can have an affected child 5) more common with inbreeding

Red-green color blindness is due to an X-linked recessive allele in humans. A widow's peak (a hairline that comes to a peak in the middle of the forehead) is due to an autosomal dominant allele. Consider the following family history: A man with a widow's peak and normal color vision marries a color-blind woman with a straight hairline. The man's father had a straight hairline, as did both of the woman's parents. Use the family history to make predictions about the couple's children. 1. If the couple has a child, what are the chances that it will be a son with a widow's peak? 2. What is the chance that any son the couple has will be colorblind with a straight hairline? 3. What is the chance that any daughter the couple has will be colorblind with a widow's peak? 4. Suppose the couple has a daughter with normal color vision and a widow's peak. What is the chance she he heterozygous for both genes?

1. 1/4 2. 1/2 3. 0 4. 1 (For the hairline gene, the man's genotype is Ww and the woman's is ww. For the color vision gene, the man's genotype is X N Y and the woman's is X n X n. Because the genes are on different chromosomes, they assort independently. Also, because one gene is sex-linked, it exhibits a different inheritance pattern in males and females. You should use the multiplication rule to calculate the chances of two events (e.g., widow's peak and colorblindness) occurring together in a specific combination, paying attention to whether the offspring is male or female.)

2 situations for meiotic recombination to occur

1. genes on different chromosomes that independently assort 2. genes near each other on the same chromosome (linked) and we get crossing over

A sex-linked recessive allele produces a red-green color-blindness in humans. A normal woman named Kate whose father was color-blind marries a color blind man named William. Of all of the children (sex unspecified) of these parents, what proportion can be expected to have normal vision?

1/2

A sex-linked recessive allele produces a red-green color-blindness in humans. A normal woman named Kate whose father was color-blind marries a color blind man named William. Of the girls produced from this couple, what proportion can be expected to be colorblind?

1/2

Huntington disease is a rare, fatal, degenerative neurological disease in which individuals start to show symptoms, on average, in their 40s. It is caused by a dominant allele. Joe, a man in his 20s, just learned that his father has Huntington's disease. What is the probability that Joe will also develop the disease?

1/2 (since it is a dominant disorder, a homozygote is rare, so his dad is probably heterozygous and his mom probably does not have it since it is rare)

For incomplete dominance, what phenotype would you expect from this cross: R1R1 x R1R2 1 is red, and 2 is white

1/2 pink, 1/2 red

For incomplete dominance, what phenotype would you expect from this cross: R2R2 x R1R2 1 is red, and 2 is white

1/2 pink, 1/2 white

A rare autosomal-recessive allele inherited in a Mendelian manner causes the disease cystic fibrosis. A phenotypically normal man whose father had cystic fibrosis marries a phenotypically normal woman from outside the family, and the couple consider having a family. If the frequency in the population of heterozygotes in 1 in 50, what is the chance that the couple's first child will have cystic fibrosis?

1/200 (there is a 1/2 chance that he will give the diseased allele to a child, there is a 1/50 chance that his wife carries the allele, and if she carries it, there is a 1/2 chance that she will give it)

Dwarfism in humans is a dominant trait that is also homozygous lethal. If two people with dwarfism have children, what are the expected phenotypic and genotypic ratios? Why?

1/3 has no dwarfism (dd) 2/3 (Dd) have dwarfism. The parents must be heterozygous since they have the trait, but are alive. A monohybrid cross normally gives a 3:1 ratio, but since the homozygous dominant condition is lethal, it is modified 2:1.

Huntington disease is a rare, fatal, degenerative neurological disease in which individuals start to show symptoms, on average, in their 40s. It is caused by a dominant allele. Joe, a man in his 20s, just learned that his father has Huntington's disease. Joe and his new wife have been eager to start a family. What is the probability that their first child will eventually develop the disease?

1/4

Red-green color blindness is X-linked in humans. If a male is red-green color blind, and both parents have normal color vision, which of the male's grandparents is most likely to be red-green color blind?

The maternal grandparents.

A sex-linked recessive allele produces a red-green color-blindness in humans. A normal woman named Kate whose father was color-blind marries a color blind man named William. What are the chances that the first child from this marriage will be a color-blind boy?

1/4 (Kate must be a carrier since she is normal, but had a colorblind father

For incomplete dominance, what phenotype would you expect from this cross: R1R2 x R1R2 1 is red, and 2 is white

1/4 red, 1/2 pink, 1/4 white

Suppose that a couple has a 1/4 chance of having a son with a widow's peak and a 1/2 chance of having a color-blind son. The couple's chances of having a son with both a widow's peak and colorblindness would be _____.

1/8 (When two events occur independently, you can use the multiplication rule to calculate the probability of the two events occurring together in a specific combination. In this case, the chances of having a son with both a widow's peak and colorblindness would be 1/4 x 1/2 = 1/8. Although you can get the same result using a Punnett square for a dihybrid cross, this method becomes impractical when more genes are involved. Using the multiplication rule is preferable.)

Phenotypic ratio for duplicate dominant epistasis for a dihybrid cross

15:1

If you cross a plant that has red flowers to one that has yellow flowers, you produce a plant that has orange flowers. Then, you cross an orange flowered plant to a red flowered plant. What will the phenotypes of the offspring be, and in what proportion?

1:1 (red:orange)

For a period of several years, a scientist investigated an inherited anomaly of the nuclei of white blood cells of rabbits. This anomaly, termed the Pelger anomaly, does not seem to inconvenience the rabbits. When rabbits showing the typical Pelger anomaly were mated with wildtype rabbits from a true-breeding stock, the scientist found 217 offspring with the Pelger anomaly and 237 wildtype. What appears to be the genetic basis of the Pelger anomaly?

1:1 ratio means that the Pelger anomaly is dominant and the wild type is recessive

If we testcross this dihybrid, what is the phenotypic ratio that will result in the progeny? A/a; B/b x a/a; b/b

1:1:1:1

Testcross of a dihybrid phenotypic ratio

1:1:1:1

In a certain cactus, prickly spines can be two pronged or one pronged. If a true breeding one-pronged cactus is crossed with a true breeding two-pronged cactus, the F1 generation has a mixture of spines some are two-pronged, some are one-pronged. In this same cactus, if you cross a plant that has red flowers with one that has yellow flowers, you produce an orange flowered plant. You cross a cactus that is heterozygous for both traits with one that has red flowers and one-pronged spikes. What phenotypes and in what proportion will the offspring be?

1:1:1:1 Red flowers mixed prongs: red flowers one prong: orange flowers mixed prongs: orange flowers one prong

If we testcross this dihybrid, what is the genotypic ratio that will result in the progeny? A/a; B/b x a/a; b/b

1:1:1:1 (Aa;Bb, Aa;bb, aa; Bb, aa;bb)

What phenotypic ratio would you expect as a result of a test cross between a dihybrid organism and one that is homozygous recessive for alleles at two independent loci?

1:1:1:1 (a dihybrid organism is an organism that has two pairs of contrasting traits)

Flower color in snapdragons results from the amount of the pigment anthocyanin in the petals. Red flowers are produced by plants that have full anthocyanin production, and ivory-colored flowers are produced by plants that lack the ability to produce anthocyanin. The allele An1 has full activity in anthocyanin production, and the allele An2 is a null allele. Dr. Ara B. Dopsis, a famous genetic researcher, crosses pure-breeding red snapdragons to pure-breeding ivory snapdragons and produces F1 progeny plants that have pink flowers. He proposes that this outcome is the result of incomplete dominance, and he crosses the F1 to test his hypothesis. What phenotypic ratio will be in the F2?

1:2:1

Phenotypic ratio for incomplete dominance when 2 heterozygotes are crossed

1:2:1

With incomplete dominance, a likely ratio of phenotypes in the F2 generation resulting from a monohybrid cross between two true-breeding parents would be ______.

1:2:1

In a certain cactus, prickly spines can be two pronged or one pronged. If a true breeding one-pronged cactus is crossed with a true breeding two-pronged cactus, the F1 generation has a mixture of spines some are two-pronged, some are one-pronged. You cross 2 of the cacti from the F1 generation. What are the phenotypes of the F2 offspring, and in what proportion?

1:2:1 two pronged: mixed: one pronged

Phenotypic ratio for codominance when 2 heterozygotes are crossed

1:2:1 (modified monohybrid 3:1)

Most of the feathers of erminette fowl are light colored, with an occasional black one, giving a flecked appearance. A cross of two erminettes produced a total of 48 progeny, consisting of 22 eminettes, 14 blacks, and 12 pure whites. What genetic basis of the erminette pattern is suggested? How would you test your hypothesis?

1:2:1 ratio indicates codominance Test: mate a black to a white and see if all of the offspring are flecked, which will confirm codominance

How many copies of a dominant lethal allele are needed to cause lethality? Why are dominant lethal alleles so rare in a population?

1; For these alleles to exist in a population, the affected individuals must reproduce before the lethal allele can be expressed, so if all affected individuals die before reproducing, the mutant allele will not be passed to future generations

How many alleles does one diploid organism have for a gene for the ABO blood type?

2

How many copies of a recessive lethal allele are needed to cause lethality?

2

In mice, dwarfism is caused by an x-linked recessive allele, and a pink coat is caused by an autosomal dominant allele (coats are usually brown). If a dwarf female from a pure line is crossed with a pink male from a pure line, how many genes are involved?

2

What if two genes are linked on one chromosome and there is no crossing over between homologs (complete linkage). How many gamete combinations are possible?

2 (just equal segregation of the two homologous alleles into each gamete)

In a mating of mice with the genotypes AYaBb x AYaBb , what is the probability that a live-born offspring will have yellow fur?

2/3 (Because the presence of the AY allele is epistatic to (masks expression of) the B/b gene, the B/b gene does not need to be taken into consideration in this problem. For the AYa x AYa cross, 1/4 of the offspring would have the AYAY genotype, which is lethal before birth. For the live-born offspring, 2/3 would be AYa, and thus have yellow fur.)

A couple comes to a genetic counselor concerned about their chances of having a baby with Tay Sachs disease. The husband had a sibling die of the disease, which is inherited as a autosomal recessive trait. What are the chances that he is a carrier?

2/3 (His parents' children had a 25% of having an affected child, a 50% chance of having a carrier and a 25% non carrier. Since the husband didn't die of Tay Sachs, he is in one of the latter two categories, which should be produced in a 2:1 ratio.)

In foxes, two alleles of a single gene, P and p, may result in lethality (PP), platinum coat (Pp), or silver coat (pp). What ratio is obtained when platinum foxes are interbred?

2/3 platinum, 1/3 silver

A dihybrid was crossed to a tester (dg/dg). The result of the cross was: 40% Dg/dg; 40% dG/dg; 10% DG/dg and 10% dg/dg. How far apart are genes D and G on the chromosome ?

20 m.u. because 20% of the gametes are recombinants

In peas, axial (A) flower position is dominant to terminal (a), tall (L) is dominant to short (l), and yellow (Y) is dominant to green (y). If a plant that is heterozygous for all three traits is allowed to self-fertilize, how many of the offspring would be dominant for all three traits?

27/64

Recognizing recessive lethality. What ratio would you expect from mating two heterozygotes?

2:1 generally if there are no survivors

What would be the expected frequency of agouti brown offspring in the litter?

3/16 (Because the two traits are determined by unlinked genes, they assort independently. As a result, you need to use the multiplication rule to calculate the probability of agouti brown offspring (A_ bb) from AaBb parents. The probability of A_offspring is 3/4, and the probability of bb offspring is 1/4. The combined probability is therefore 3/4 x 1/4 = 3/16)

If a yellow pea plant with round seeds that has the genotype GgWw is crossed to itself, what proportion of the offspring will be green with round seeds?

3/16 (This is the probability of offspring that are either green with round seeds or yellow with wrinkled seeds.)

A/a;B/b;D/d x A/a;B/b;D/d A = tall a = short B = dark b= blonde D = handsome d= ugly How many would be tall, blonde and ugly?

3/64

The following phenotypic ratios are determined for a trihybrid cross in which the gametes assort independently: A 1 : A 2 = ¼ : ¾ B 1 : B 2 = ¼ : ¾ C 1 : C 2 = ¾ : ¼ What is the probability that the F2 offspring will have the phenotype A 1 B 1 C 1?

3/64

In rats, the following genotypes of two independently assorting autosomal genes determine coat color. A_B_ (gray) A_bb (yellow) aaB_ (black) aabb (cream) A third gene pair on a separate autosome determines whether or not any color will be produced. The CC and Cc genotypes allow color according to the expression of the A and B alleles. However, the cc genotype results in albino rats regardless of the A and B alleles present. For the following cross, what fraction of the offspring would you expect to have each genotype? What are the expected phenotypic ratios? AABbCc x AABbcc A_B_C_ A_B_cc A_bbC_ A_bbcc aaB_C_ aaB_cc aabbC_ aabbcc

3/8, 3/8, 1/8, 1/8, none, none, none, none 3 gray: 1 yellow: 4 albino

A plant of genotype Ig/Ig is crossed to iG/iG and the F1 is testcrossed to ig/ig plants. If 15% percent of the offspring are ig/ig and 15% percent of the offspring are IG/Ig, this tells us what about the distance between genes i and g?

30 m.u.

Phenotypic ratio for complete dominance when 2 heterozygotes are crossed

3:1

If two genes on the same chromosome exhibit complete linkage, what is the expected F2 phenotypic ratio from a selfed heterozygote with the genotype a+b+//ab?

3:1 (Each parent produces two types of gametes, a + b + and ab, giving the simple Mendelian ratio of 3 a + b + : 1 ab.)

Which phenotypic ratios are associated with crosses dealing with a single genetic locus? Select all that apply. 9:3:3:1 3:1 1:1:1:1 1:2:1 1:1 9:7

3:1 is a monohybrid cross 1:2:1 is incomplete or codominance 1:1 is a heterozygous test cross

Explain what happens when two genes on two different chromosomes independently assort, how many different gamete combinations are possible?

4

What if two genes are linked on one chromosome and there is a crossover between two non-sister chromatids. How many gamete combinations are possible?

4

A SNP (G or C) at a particular location is 8 m.u. away from the beta hemoglobin gene. A woman has the genotype: Gb/CB. What percent of her gametes would have the C version of the SNP linked to the recessive beta hemoglobin?

4% of gametes

A SNP (G or C) at a particular location is 8 m.u. away from the beta hemoglobin gene. A woman has the genotype: Gb/CB. What percent of her gametes would the G version of the SNP be linked to the recessive beta hemoglobin allele?

46%

If two dihybrids are crossed, what percent of offspring will be resistant to the herbicide, glyphosphate? Will they all be high pollen producers too? r/r = wildtype (susceptible to glyphosphate), R/R = resistant to glyphosphate F/F= fertile (high pollen producer), f/f= wildtype (normal pollen producer)

75% will be resistant, and 9/16 will be resistant and high pollen producers

Out of 100 people carrying a mutation in a bone development gene only 87 have a phenotype of osteoporosis. What is the penetrance?

87% (incomplete penetrance)

What are the ratios for phenotypes for a dihybrid cross when genes are on different chromosomes:

9/16 both dominant 3/16 one dominant, one recessive 3/16 one recessive, one dominant 1/16 both recessive

If two linked genes are far enough apart and the result is a 1:1:1:1 ratio (50% parental and 50% recombinant) this would be indistinguishable from what?

Two, unlinked, independently assorting genes

In rats, the following genotypes of two independently assorting autosomal genes determine coat color. A_B_ (gray) A_bb (yellow) aaB_ (black) aabb (cream) A third gene pair on a separate autosome determines whether or not any color will be produced. The CC and Cc genotypes allow color according to the expression of the A and B alleles. However, the cc genotype results in albino rats regardless of the A and B alleles present. For the following cross, what fraction of the offspring would you expect to have each genotype? What are the expected phenotypic ratios? AaBBCc x AaBBCc A_B_C_ A_B_cc A_bbC_ A_bbcc aaB_C_ aaB_cc aabbC_ aabbcc

9/16, 3/16, none, none, 3/16, 1/16, none, none 9 gray: 3 black: 4 albino

In the same mouse species, a fourth unlinked gene (gene P/p) also affects fur color. For mice that are either homozygous dominant (PP) or heterozygous (Pp), the organism's fur color is dictated by the other three genes (A/a, B/b, and C/c). cc is epistatic to the A and B genes and black is B_ and solid color is aa. For mice that are homozygous recessive (pp), large patches of the organism's fur are white. This condition is called piebaldism. In a cross between two mice that are heterozygous for agouti, black, color, and piebaldism, what is the probability that offspring will have solid black fur along with large patches of white fur?

9/256 (Because each gene segregates independently, you need to determine the probability of each genotype independently and then multiply the four probabilities together. The probability of offspring with solid color (aa) is 1/4; the probability of offspring with black fur (BBor Bb) is 3/4; the probability of colored fur (CCor Cc) is 3/4; and the probability of piebald, or white patches (pp), is 1/4. The combined probability is1/4 x 3/4 x 3/4 x 1/4 = 9/256.)

In rats, the following genotypes of two independently assorting autosomal genes determine coat color. A_B_ (gray) A_bb (yellow) aaB_ (black) aabb (cream) A third gene pair on a separate autosome determines whether or not any color will be produced. The CC and Cc genotypes allow color according to the expression of the A and B alleles. However, the cc genotype results in albino rats regardless of the A and B alleles present. For the following cross, what fraction of the offspring would you expect to have each genotype? What are the expected phenotypic ratios? AaBbCc x AaBbcc A_B_C_ A_B_cc A_bbC_ A_bbcc aaB_C_ aaB_cc aabbC_ aabbcc

9/32, 9/32, 3/32, 3/32, 3/32, 3/32, 1/32, 1/32 9 gray: 3 yellow: 3 black: 1 cream: 16 albino

Phenotypic ratio for dominant epistasis for a dihybrid cross

9:3:1

Assuming independent assortment, what phenotypic ratio would you expect to see if an individual with the genotype RrGg is self-crossed?

9:3:3:1

Phenotypic ratio for recessive epistasis for a dihybrid cross

9:3:4

Phenotypic ratio for duplicate recessive epistasis for a dihybrid cross

9:7

White Precursor 1 --> White Precursor 2 --> blue A white precursor is taken by an enzyme (A) and made into a 2nd white precursor and then is taken by another enzyme (B) and is turned into a blue pigment. If we lose the function of A, we cannot make white precursor 2, and if we lose the function of enzyme B, we cannot take the precursor 2 to make the blue pigment, so we need both enzymes to get the blue pigments in flowers. What is the phenotypic ratio when 2 dihybrids are crossed

9:7 (blue: white)

cis configuration

A dihybrid with both dominant genes on one chromosome and both recessives on the other

What is the phenotype of a heterozygote if there is incomplete dominance?

A phenotype intermediate of the phenotypes of the two parents.

Mutant alleles in the CFTR gene demonstrate this. In individuals with cystic fibrosis, there is lung disease, sterility, and pancreatic dysfunction from a single gene defect. Why? The gene product, the CFTR protein, has important functions in the cells of the respiratory, digestive, and reproductive tracts. If both CFTR genes are mutant, then we will only see the effects in the cells that this protein is normally expressed within. This is an example of what:

A pleiotropic allele An allele that affects several properties of an organism

What is pleiotrophy and how does Marfan syndrome illustrate its definition?

A single mutation can cause multiple phenotypic effects. Marfan syndrome results from a single autosomal dominant mutation in a gene coding for a connective tissue protein, and because this protein is widespread in many tissues in the body, we see the affect of the mutation in the lens of the eye, the lining of vessels, such as the aorta, bones, to other tissues.

Hereditary deafness is a heterogeneous trait, meaning what?

A single phenotype, hereditary deafness, can be caused by mutations in a bunch of different genes

What is a test cross and give an example?

A testcross is a cross between an individual whose genotype at one or more loci may be unknown and an individual who is homozygous recessive for the gene or genes in question; to distinguish a homozygous dominant with a heterozygous (A/a x A/A is a testcross)

In sweet peas, the two allelic pairs C, c and P, p are known to affect pigment formation in the flowers. The dominants, C&P, are both necessary for colored flowers. Absence of either results in white flowers. A dihybrid plant is crossed to a white one that is heterozygous at the "C" locus. A) What is the genotype of the dihybrid plant? B) What is the genotype of the white plant? C) What kinds of flowers, colored or white, are to be expected from the cross above? Include the ratio. D) Assume that another allelic pair in sweet peas also affects pigment formation in addition to the genes mentioned above. The presence of the dominant, R, is required for red flowers. It's recessive allele, r, produces yellow flowers. What would be the phenotypes of the following plants in relation to flower color? a. CcPpRr b. CcppRR c. CcPPrr d. ccPPRR

A) CcPp B) Ccpp C) Colored (C-P-), 3/8 White (cc-- or --pp), 5/8 D) a. CcPpRr Red b. CcppRR White c. CcPPrr Yellow d. ccPPRR White

Why does crossing over occur more often between two distantly linked genes than between two closely linked genes on the same chromosome?

Crossing over is somewhat randomly distributed over the length of the chromosome. Two loci that are far apart are more likely to have a crossover between them than two loci that are close together.

T/F: Independent assortment occurs only in cells that are heterozygous for two genes (AaBb) and not in cells that are completely homozygous (AABB or aabb).

False (Even though there would be no genotypic differences in the products of such meioses, random alignment of chromosomes would still have occurred.)

Independent assortment explains _______. A) why a collection of meiotic products that includes gametes of genotype Ab will also include gametes of genotype AB in roughly the same proportion B) why meiosis in a cell of genotype Aa yields A gametes and a gametes, but no Aa gametes C) why meiosis in a cell of genotype AaBb cannot yield Ab gametes D) why meiosis in a cell of genotype Aa yields A gametes and a gametes in roughly equal numbers

A) why a collection of meiotic products that includes gametes of genotype Ab will also include gametes of genotype AB in roughly the same proportion (Because alignment of the chromosomes is random, the alignment that produces Ab is just as likely as the alignment that produces AB. Therefore, the two genotypes should both occur with equal frequency.)

What are 3 dihybrid genotypes?

A/a;B/b (genes on different chromosomes ) AB/ab (linked genes in the cis configuration) Ab/aB (linked genes in the trans configuration)

What four gametes can be made from a dihybrid that is AB on one chromosomes and ab on the other if there is a single crossover between non sister chromatids

AB, Ab, aB, ab

What types of gametes will form from a dihybrid and in what ratios?

AB, Ab, ab, aB 1:1:1:1

When these two are crossed, what gametes will form? Which are the parental, and which are the recombinant? AB/ab x ab/ab

AB/ab (p), ab/ab (p), Ab/ab (r), aB/ab (r)

trans configuration

Ab/aB; A dihybrid with one dominant genes and one recessive on one chromosome and the opposite dominant and recessive on the other

When these two are crossed, what gametes will form? Which are the parental, and which are the recombinant? Ab/aB x ab/ab

Ab/ab (p), aB/ab (p), AB/ab (r), ab/ab (r)

Parental gametes: AB and ab Dihybrid x tester: AB/ab x ab/ab Progeny: AB/ab - 78 ab/ab - 82 Ab/ab - 19 aB/ab - 21 Which are the recombinants? How far apart are the genes?

Ab/ab and aB/ab 20 m.u.

What is a complementation group?

All mutations of a single gene

For incomplete dominance, what phenotype would you expect from this cross: R1R1 x R2R2 1 is red, and 2 is white

All pink

Why, when genes are linked, do we not see a 1:1:1:1 ratio in the F2s that we see with independent assortment?

Alleles tend to stick together, and crossing over depends on the distance between the genes; not equally likely

T/F or an assumption: Individuals from outside the family that join through marriage or reproduction are not carriers

Assumption. For a rare disease this is usually true, but there is still a chance. If, for example, the outsider and the other parent are unaffected but have an affected child, you know they must both be carriers.

T/F or an assumption: Autosomal recessive traits are rare

Assumption. This is usually true when talking about diseases, but some recessive traits are common (for example, cleft chin is a recessive but pretty common)

Why are most affected individuals with an autosomal dominant disease usually heterozygotes (Aa) and not homozygotes (AA)?

Autosomal dominant disorders are very rare in the population, so it is highly unlikely that the infected individual inherited a copy from both parents, and furthermore if a mutation is dominant, a single copy is enough to produce the mutant phenotype, and homozygotes will probably be even more severely affected nad might not even survive

What kind of gametes can an individual with the genotype Bb;Dd make?

BD, Bd, bD, and bd

What kind of gametes can an individual with the genotype Bb;DD make?

Bd and bd

The Bombay phenotype illustrates illustrates epistasis because an individual with the genotype h/h; iA/iB will NOT have blood AB, they will be blood type O. Why? Explain.

Because the mutant form of FUT1 gene masks the expression of IA and IB alleles, where one locus masks the other locus. A and B antigens are carbohydrate groups that are bound to the lipid molecules protruding from the membrane of the red blood cell. The specificity of the A and B antigens is based n the terminal sugar of the carbohydrate group. Both the A and B antigens are derived from a precursor molecule, called the H substance. If there is a mutation in the FUT1 gene and a person has 2 copies of that mutant allele (it is recessive), the person will have O blood type because this prevents the synthesis of the H substance and even though they may have the IA and/or IB, alleles, neither the A nor B antigen can be added to the cell surface. The homozygous presence of the FUT1 mutant masks IA and IB alleles

T/F: The larger the number of total individual counts in a chi-square test, the higher the degrees of freedom (df).

False (df increases with increasing n (number of categories), but not necessarily with increasing number of subjects.)

Eye color in Drosophila is an X-linked trait. White eyes is recessive to red eyes. If a Drosophila male has white eyes, which of the following must also be true? A) All his male siblings from the same parents must also have white eyes. B) Some of his female siblings from the same mating must also have white eyes. C) His mother had at least one white allele. D) His father must also have had white eyes.

C) His mother had at least one white allele.

Of the methods listed below, which would be the best way to determine which of two alleles of a gene is dominant to the other? A) Count the number of recessive individuals resulting from a cross between two recessive parents. B) Perform crosses between series of randomly selected pairs to see which phenotype occurs more frequently. C) Observe the relevant phenotype in the progeny that result from a cross between individuals from two different pure-breeding lines. D) Observe the relevant phenotype among the progeny of several crosses between individuals within a single, pure-breeding line.

C) Observe the relevant phenotype in the progeny that result from a cross between individuals from two different pure-breeding lines.

Which of the following statements about an individual with the Bombay phenotype is correct? A) The individual lacks the IA allele. B) The individual lacks the enzyme required to modify the H substance. C) The individual lacks the enzyme required to produce the H substance. D) The individual lacks the IB allele.

C) The individual lacks the enzyme required to produce the H substance. (Individuals with the Bombay phenotype are homozygous hh and do not make the enzyme required to produce the H substance. Thus, they cannot modify the H substance to produce the antigens on which type A and B blood phenotypes are based.)

Let's pretend it is now modern times and this couple with no pregnancies yet came to a genetic counselor with their family history. What might be done ?

Carrier test of mom, then dad, and possibly, prenatal or preimplantation tests.

How does an environmental condition such as temperature alter phenotype? Give an example.

Chemical activity depends on the kinetic energy of the reacting substances which in turn depends on the surrounding temperature. An example is seen in Siamese cats and Himalayan rabbits, which exhibit dark fur in certain regions where their body temperature is cooler (nose, ears, paws). In these cases, it appears that an enzyme normally responsible for pigment production is functional only at the lower temperatures present in the extremities, but it loses its catalytic function at higher temperatures found throughout the rest of the body

Was the parent in the cis or the trans configuration when crossed to a tester? Progeny: 30% AB/ab; 30% ab/ab; 20% Ab/ab; 20% aB/ab.

Cis since the parental gametes are more common and the more common are cis

In a certain cactus, prickly spines can be two pronged or one pronged. If a true breeding one-pronged cactus is crossed with a true breeding two-pronged cactus, the F1 generation has a mixture of spines some are two-pronged, some are one-pronged. Is this an example of codominance or incomplete dominance?

Codominance

How do we find the distance between 2 genes of interest?

Cross a dihybrid to a tester and then find the recombinant frequency

When doing a complementation test, how can we make sure that our mutants are homozygous recessive?

Cross them with wildtype phenotype and we should always see wildtype progeny in F1

True or false. Wildtype is the dominant allele

False. Often, but not always

iA/iB; H/h x iA/iB; H/h . What will the phenotypic ratios of blood type be?

Type A: 0.1875 Type B: 0.1875 Type AB: 0.375 Type O: 0.25

Which of these statements are TRUE? A) A "superweed" would die if the leaves were sprayed with glyphosate. B) A "superweed" would survive if sprayed with an older herbicide, such as Dicambra or 2,4D. C) A genetically modified crop, with the altered EPSPS gene, would survive if sprayed with an older herbicide, such as Dicambra or 2,4D. D) A genetically modified crop, with an altered EPSPS gene, would survive if the leaves were sprayed with glyphosate.

D) A genetically modified crop, with an altered EPSPS gene, would survive if the leaves were sprayed with glyphosate.

Which of the following statements about gamete formation during meiosis is false? A) Complete linkage results in the formation of only parental gametes. B) Recombinant gametes contain combinations of alleles not found in the parent cell. C) Parental gametes contain the same combinations of linked genes as found in the parent cell. D) Parental gametes can be formed only if there is no crossing over during meiosis.

D) Parental gametes can be formed only if there is no crossing over during meiosis. (If crossing over occurs, half of the gametes formed are parental and the other half are recombinant.)

White eye color is an X-linked trait in one line of fruit flies. White eyes is recessive to red eyes. If a red-eyed female and a white-eyed male are crossed, _______. A) none of their male progeny could have white eyes B) all of their female progeny will have white eyes C) all of their progeny will have white eyes D) some of their male progeny may have white eyes

D) some of their male progeny may have white eyes (If the female is heterozygous, approximately half of the male progeny will have white eyes.)

If brown is the dominant color for seeds and I give you a plant with brown seeds, do you automatically know its genotype? How can you figure it out?

Do a test cross! Cross it with a plant that is homozygous recessive for the other trait and if all of the offspring are brown, we know the seed was homozygous dominant. If we have 1/2 brown progeny, we can say the seed was heterozygous

Fruit color in summer squash is controlled by two genes, "W" and "Y." The W gene controls whether or not the fruit is white or colored. If the squash is colored, the Y gene determines which color - yellow or green - the fruit will be. Yellow is dominant to green. You perform many dihybrid crosses with heterozygotes, which are white. The data from the crosses are listed below: P Generation: WwYy x WwYy F1 Generation: White - 121 Yellow - 29 Green - 10 Is this an example of dominant epistasis or recessive epistasis?

Dominant epistasis 12:3:1

Gene A and Gene B make protein products that are duplicates (redundant). That means, if either A or B is present the kernel will be colored. In the absence of A and B the kernel is white. What ratio will you get if two dihybrids are crossed (A/a; B/b)?

Dominant epistasis 15:1 (colored:not colored)

In foxes, two alleles of a single gene, P and p, may result in lethality (PP), platinum coat (Pp), or silver coat (pp). Is the P allele behaving dominantly or recessively in causing platinum coat color?

Dominantly

We used to think a cancer like prostate cancer was similar in each patient, what do we now know?

Each cancer can be very different and can be broken down based on many different types of gene mutations and expression characteristics and each tumor is different genetically

Epistasis

Epistasis is an example of gene interaction where the expression of one gene or gene pair modifies or masks the expression of another gene or gene pair

Mendel's law of segregation predicts which phenotypic ratios among the F1 and F2 progeny from crosses between two pure-breeding parents for a single trait (e.g., yellow vs. green peas).

F1 1:0 F2 3:1 A monohybrid cross for a dichotomous trait always yields a single phenotype (the dominant trait) in the F1 and a 3:1 phenotype ratio (3 dominant : 1 recessive) in the F2.

The inheritance of eye color in Drosophila is controlled by genes on each of the fly's four chromosome pairs. One eye-color gene is on the fly's X chromosome, so the trait is inherited in a sex-linked manner. For this sex-linked trait, the wild-type (brick red) allele is dominant over the mutant vermilion (bright red) allele. A homozygous wild-type female fly is mated with a vermilion male fly. (X+X+ with XpY) Predict the eye colors and ratio of F1 and F2 generations. (Assume that the F1 flies are allowed to interbreed to produce the F2 generation.) F1 females: F1 males: F2 females: F2 males:

F1 females: all WT F1 males: all WT F2 females: all WT F2 males: 1/2 WT, 1/2 vermilion

When true breeding brown dogs are mated with certain true breeding white dogs, all the F1 progeny are white. The F2 progeny from some F1 x F1 crosses were: 118 white, 32 black, 10 brown. What are the genotypes for each phenotype in the F1, F2, and parental?

F2: White: A/-; B/- and A/-;b/b Black: a/a;B/b Brown: a/a;b/b F1: White: A/a;B/b Parental: White: A/A;B/B Brown: a/a;b/b

T/F: The law of independent assortment states that one gene in a pair is always dominant to the other.

FALSE

T/F: Expressivity is the term used to describe the balanced genetic output from a hemizygous condition.

False

T/F: Linkage (viewed from results of typical crosses) always occurs when two loci are on the same chromosome.

False

T/F: Penetrance specifically refers to the expression of lethal genes in heterozygotes.

False

T/F: Crossing over during prophase I of meiosis occurs between alleles on sister chromatids

False (Crossing over during meiosis occurs between alleles on nonsister chromatids.)

Penetrance

the number of individuals with a particular genotype that demonstrate the expected phenotype.

Explain how super weeds became resistant to glyphosphate

Glyphosate inhibits an enzyme called EPSPS that builds three essential amino acids in plants and bacteria but, crucial to its widespread adoption, not in animals. Some plants had a mutation that produced extra EPSPS enzyme, and not all of it bound the herbicide, so the plant could still grow and it passed on its mutant allele

A certain breed of parrot can produce two types of pigment in its feathers - blue and yellow. These pigments are controlled by two different genes that assort independently. For both of these genes, "produces pigment" is dominant and "doesn't produce pigment" is recessive. A bird that produces both yellow and blue pigment will have green feathers and a bird that produces neither pigment will have white feathers. In a dihybrid cross of two green parrots (Yy x Bb)... What phenotypes are possible, and in what ratio?

Green: 9/16 Yellow: 3/16 Blue: 3/16 White: 1/16

When rabbits with the Pelger anomaly were mated with each other, the scientist found 223 wildtype progeny, 439 with the Pelger anomaly, and 39 extremely abnormal progenies with defective white blood cells and skeletal abnormalities. What do these 39 rabbits represent in genetic terms? Why were there only 39?

Homozygote dominant for the Pelger died out. If you have 2 copies of the Pelger allele, this is dominant and they will die

Who is crossed in a complementation test?

Homozygous recessive mutants (cross the mutants to each other)

Most combinations of different ABO alleles result in complete dominance of one allele. Which combination results in codominance?

IAIB

What is complementation?

If we cross 2 homozygous recessive mutants and get the wildtype phenotype back, meaning that the phenotypes are from different genes

What is the difference between incomplete dominance and codominance?

In codominance, both phenotypes are expressed in heterozygotes, and each allele expresses itself and there is no mixing. In incomplete dominance, the heterozygote shows a phenotype that is intermediate between the two homozygotes. In both types of inheritance, the heterozygote shows a phenotype that is distinct from either homozygote; in incomplete dominance, the expressed phenotype will not specifically have its own allele

What is crossing over?

In meiotic prophase, alleles on the same chromosome get shuffled around with the alleles from the genes on the other homolog; recombination

If you cross a plant that has red flowers to one that has yellow flowers, you produce a plant that has orange flowers. Is this codominance or incomplete dominance?

Incomplete

In pedigree analysis, which of the following is a hallmark of an autosomal recessive disorder? A) Each individual who has the disease has at least one affected parent. B) Two unaffected parents will not have any children with the disease. C) Individuals who have the disease are commonly born to normal (unaffected) parents. D) Two affected parents may produce unaffected children.

Individuals who have the disease are commonly born to normal (unaffected) parents.

Can a prenatal test determine if a baby will have Alzheimers? Why or why not?

It can see if they have a gene that may make them susceptible, but diseases like Alzheimers are caused by interactions between many genes, epigenetic factors, lifestyle, and the environment.

In the 18th century, a young boy suffered from a skin condition that included thickening of the skin and the formation of loose spines that were periodically sloughed off. This "porcupine man" married and had six sons, all of whom had the same condition. He also had several daughters, all of whom were unaffected. What might you theorize about the location of the abnormal gene?

It could be on the Y chromosome, because like the Y it is transmitted from fathers to sons, and females do not have Y chromosomes, hence the reason all of his daughters were not affected

The genes M and T are found on chromosome #2 in roundworms and they are 12 map units apart. If we crossed a cis dihybrid with a tester, what do we expect the genotypes of the offspring to be and in what frequency?

MT/mt: 44% mt/mt: 44% mT/mt: 6% Mt/mt: 6%

You discover a new species of fish that are normally gray and have round white eyes. Mutations in the black gene cause the fish to be black in color. Mutations in the star gene cause the fish to have star shaped eyes. You want to map the location of black gene relative to the star gene. You cross a dihybrid female with a black, star eye male and you get the following progeny: 155 wildtype 165 black, star eyes 220 gray, star eyes 350 black, round eyes Write out the genotype of the male and female parental fish using two lines to indicate the orientation of the alleles on the chromosomes. What is the map distance in map units between black and star?

Male: bs/bs (tester) Female: bs+/b+s (trans dihybrid) 32 m.u.

In mice, dwarfism is caused by an x-linked recessive allele, and a pink coat is caused by an autosomal dominant allele (coats are usually brown). If a dwarf female from a pure line is crossed with a pink male from a pure line, what are the genotypes and phenotypes of the F1 male and F1 female mice?

Males: all dwarf and all pink (XdY;Pp) Females: all normal sized and all pink (XDXd;Pp)

Phenotype

the physical appearance of a trait

Locus

the place on a chromosome where a gene is located

A certain breed of parrot can produce two types of pigment in its feathers - blue and yellow. These pigments are controlled by two different genes that assort independently. For both of these genes, "produces pigment" is dominant and "doesn't produce pigment" is recessive. A bird that produces both yellow and blue pigment will have green feathers and a bird that produces neither pigment will have white feathers. In a dihybrid cross of two green parrots (Yy x Bb), we get a different genotypic and phenotypic ratio. Why?

More than one genotype can produce the same phenotype. Green: YYBB (1/16) YYBb (2/16) YyBB (2/16) YyBb (4/16) 1+2+2+4 = 9 Yellow: YYbb (1/16) Yybb (2/16) 1+2 = 3 Blue: yyBB (1/16) yyBb (2/16) 1+2 = 3 White: yybb (1/16) 1 = 1

Meiotic Recombination

New combinations of alleles provide variation as the "raw material for natural selection"

What does it mean if alleles are written as M1, M2, M3, M4 etc.?

No dominance exists between these alleles, and the 1, 2, 3, 4, etc. superscripts just denote alternate alleles.

Think about a tall, yellow pea plant crossed to a short, green pea plant. Do offspring of all future generations look exactly like one of these parent plants?

No! New combinations can occur, such as tall and green and short and yellow

You have 3 turtles, each suffering from an autosomal dominant disease that causes them to have strange polka dotted pattern on their shells. Would a complementation test be useful for determining whether the alleles causing the disease are in the same gene or in different genes?

No, a complementation test will only work for recessive traits.

The expression of genotype will not always be the same. Describe what is meant by penetrance and expressivity.

Penetrance is the percentage of individuals who show some degree of expression of the mutant phenotype and expressivity is the range of expression for the mutant phenotype

Flower color in snapdragons results from the amount of the pigment anthocyanin in the petals. Red flowers are produced by plants that have full anthocyanin production, and ivory-colored flowers are produced by plants that lack the ability to produce anthocyanin. The allele An1 has full activity in anthocyanin production, and the allele An2 is a null allele. Dr. Ara B. Dopsis, a famous genetic researcher, crosses pure-breeding red snapdragons to pure-breeding ivory snapdragons and produces F1 progeny plants that have pink flowers. He proposes that this outcome is the result of incomplete dominance, and he crosses the F1 to test his hypothesis. What phenotypes does Dr. Dopsis predict will be found in the F2?

Pink, ivory, and red

Red (R) and yellow (r) tomatoes Single-lobe fruit (T) and two-lobed fruit (t) A red single-lobed plant is crossed with a red-two lobed plant. The offspring are: 3/8 red, single-lobed 3/8 red, two-lobed 1/8 yellow, single-lobed 1/8 yellow, two-lobed What are the genotypes of the parents, assuming independent assortment?

R/r;T/t x R/r;t/t (note the ratio of red to yellow is 3:1 and note the ratio of single to two-lobe is 1:1. When its independent assortment just look at one trait at a time.

In peas, the round allele is dominant over the wrinkled allele. If a plant with round peas is crossed to a plant with wrinkled peas, all of the resulting plants have round peas. What is the genotype of the parents in this cross?

RR × rr

What is the most likely mode of transmission for a trait that is not expressed in parents but is expressed by one half of the sons?

Rare X-linked recessive

In a genetics lab, a student who is type O finds out his parents are AB and O, how did he inherit his blood type? What are the possible genotypes for the parents and the child?

Recessive epistasis! The parents can be: IAIB; Hh x II; Hh or IAIB; hh or II; hh or IAI; hh or IBI; hh and the child is IAI; hh or IBI; hh and the hh masks the blood type genes

How are x-linked recessive disorders different from autosomal recessive disorders?

Recessive, lethal x-linked disorders, in comparison to recessive autosomal disorders, will only occur in males because the only sources of the lethal allele in the population are females who are carriers and do not express the disorder. They pass the allele onto ½ of their sons, who develop the disorder because they are hemizygous, and rarely reproduce.

In foxes, two alleles of a single gene, P and p, may result in lethality (PP), platinum coat (Pp), or silver coat (pp). Is the P allele behaving dominantly or recessively in causing lethality?

Recessively

What phenotypic ratios are expected with two independently assorting traits when two dihybrids are crossed? Aa;Bb x Aa;Bb Assume A is tall, a is short, B is yellow, b is green

Tall, yellow: 9/16 Tall, green: 3/ 16 Short, yellow: 3/16 Short, green: 1/16

What does the word recombination mean?

The crossing over and reshuffling of alleles that occurs during prophase in meiosis I. The frequency of crossing over between any two loci on a single chromosome is proportional to the distance between them.

Law of independent assortment

The law of independent assortment states that during gamete formation, segregating pairs of unit factors assort independently of each other; the law says nothing about dominance.

Although someone who is a carrier of Tay-Sachs disease is phenotypically normal, why might we see an intermediate at the gene product level?

The mutant allele inhibits activity of the enzyme hexosaminidase, and heterozygotes express about 50% of the normal enzyme activity found in homozygotes for the normal alleles, but 50% of the enzyme activity is enough to achieve normal biochemical functioning

What is complete penetrance?

The percent of people with a particular genotype that have the phenotype is 100%.

What is incomplete penetrance?

The percent of people with a particular genotype that have the phenotype is not 100%.

When a complementation test is performed, and 2 mutants with the same phenotype are crossed and their offspring are wild-type, what can we conclude?

The phenotypes are results of different genes and the genes have complemented each other

proband

The proband is the affected individual who is first brought to the attention of a medical researcher; usually the pedigree is constructed around this individual.

In fruit flies, large wings (w+) are dominant to small wings (w) and pink eyes (p+) are dominant to white eyes (p). A pure breeding large winged, pink eyed fly was crossed to a pure breeding small winged, white-eyed fly. All of the F1 offspring had large wings and pink eyes. One of the F1 offspring was crossed to a tester and the progeny are listed below: Large wings, pink eyes: 25 Small wings, white eyes: 25 Large wings, white eyes: 5 Small wings, pink eyes: 5Are these genes for wings and eyes linked or unlinked, how can you tell? If they are linked, how far apart are they? Next to each of the F2 progeny, write the genotype in the correct designation.

They are linked since the progeny are not in a 1:1:1:1 ratio that we would expect with a dihybrid and a tester. They are 16.67 m.u. away since there is a 16.7% recombination frequency. Large wings, pink eyes: w+p+/wp Small wings, white eyes: wp/wp Large wings, white eyes: w+p/wp Small wings, pink eyes: wp+/w

What does it mean when we say two genes are linked?

They are on the same chromosome and are transmitted as a single unit because the chromosomes, not the genes, are the units of transmisiion during meiosis. Linked genes are thus not free to undergo independent assortment.

It is 1965, before diagnostic genetic tests could be performed for Taysach's disease, an autosomal recessive disorder. A husband and wife each had an uncle that died from Taysach's disease. They go see a genetic counselor to find out if they are at risk for having a child with Taysach's. What would you tell them if you were the counselor?

They have a 1/36 chance of having a child with the disease ((2/3)*(1/2)*(1/2)*(2/3)*(1/4)=1/36)

In rats, the following genotypes of two independently assorting autosomal genes determine coat color. A_B_ (gray) A_bb (yellow) aaB_ (black) aabb (cream) A third gene pair on a separate autosome determines whether or not any color will be produced. The CC and Cc genotypes allow color according to the expression of the A and B alleles. However, the cc genotype results in albino rats regardless of the A and B alleles present. For the following cross, what fraction of the offspring would you expect to have each genotype? AaBBCC x AABbcc A_B_C_ A_B_cc A_bbC_ A_bbcc aaB_C_ aaB_cc aabbC_ aabbcc

They will all be A_B_C

Why would you perform a chi square analysis?

To see if observed deviations from the expected result is due to change or something more than chance

How do the patterns of inheritance change if the gene is on the X chromosome and it is a recessive disorder?

Traits are more prevalent in males and are never passed from affected fathers to their sons

T/F: "Gain of function" mutations are generally dominant because one copy in a diploid organism is sufficient to alter the normal phenotype.

True

T/F: Assume that a mutation occurs in the gene responsible for the production of hexosaminidase A, such that only about 50% of the enzyme activity is found in the heterozygote compared with a homozygous normal individual. If heterozygotes are phenotypically normal, we would say that the mutant allele is recessive to its normal allele.

True

T/F: If two gene loci are on nonhomologous chromosomes, genes at these loci are expected to assort independently.

True

T/F: In a cross between two strains that are true breeding for purple and white flowers, the F2 phenotypic ratio would be ¼ purple, ¼ white, and ½ lavender if the flower color phenotype exhibits incomplete dominance.

True

T/F: With multiple alleles, there can be more than two genetic alternatives for a given locus.

True

T/F: For X-linked traits in Drosophila, the male phenotype is determined by the maternally inherited allele.

True (Males inherit only one X chromosome. That chromosome is contributed by the female parent.)

T/F: The 3:1 phenotypic ratio observed among progeny of an F1 X F1 cross requires random union of gametes.

True (The 1:2:1 genotypic ratio represents relative probabilities of gamete combinations based on the assumption that gamete union is random.)

T/F or an assumption: X-linked traits never show father-to-son transmission

True! Rule. Fathers always give sons a Y chromosome, not an X.

T/F or an assumption: Individuals with an autosomal dominant disease have an affected parent

True! The individual had to inherit the dominant allele from a parent, so at least one parent must have the dominant allele and therefore also be affected.

What is a complementation test used for?

Used to determine how many genes are involved in a phenotype

Polydactyly is an autosomal dominant condition characterized by extra digits on the hands and/or feet. Some people who have the allele for polydactyly have an entire sixth finger on their hands, others only have a stump. What does this tell you about how the gene for polydactyly is expressed?

Variable expressivity

In rabbits, black fur (B) is dominant to orange fur (b). What could you do to determine the genotype of a black rabbit and how would you interpret your results?

We could do a test cross with a black rabbit with an orange rabbit. If we get all black rabbits, we know that the black rabbit it homozygous dominant, but if we get a 1:1 ratio black:orange, then the rabbit is a heterozygote

In fruit flies a mutation leads to small wings. Is this small allele dominant or recessive? How can you find out?

We do not automatically know by looking, so we can performa test cross with a homozygote that has large wings and make sure both flies are pure breeding by breeding the large winged fly with large winged flies over and over and making sure all of the offspring have large wings and doing the same for the small winged fly. If all of the F1 progeny have small wings, we know that small wings are dominant and then we will cross the F1s and if the F2s have 3:1 (small:large) we can confirm that small wings are dominant

After calculated the chi square value, you find that p = 0.26, how do you interpret this?

We fail to reject the null hypothesis, and the deviations are due to chance

What is the product law?

When we have two traits that independently assort, the combined probability is the product of the individual probabilities.

Fruit color in summer squash is controlled by two genes, "W" and "Y." The W gene controls whether or not the fruit is white or colored. If the squash is colored, the Y gene determines which color - yellow or green - the fruit will be. Yellow is dominant to green. You perform many dihybrid crosses with heterozygotes, which are white. The data from the crosses are listed below: P Generation: WwYy x WwYy F1 Generation: White - 121 Yellow - 29 Green - 10 What are the possible genotypes of the white squashes? The yellow squashes? The green squashes? If you cross two yellow squashes, is it possible to get white progeny? How about green progeny?

White: W--- Yellow: wwY- Green: wwyy You cannot cross two yellow squashes and get a white squash because neither of the parents have a W allele. However, if both parents are heterozygous for the Y allele, it is possible for them to both pass the recessive y and produce green offspring.

Consider the following family history: Bob has a genetic condition that affects his skin. Bob's wife, Eleanor, has normal skin. No one in Eleanor's family has ever had the skin condition. Bob and Eleanor have a large family. Of their eleven children, all six of their sons have normal skin, but all five of their daughters have the same skin condition as Bob. Based on Bob and Eleanor's family history, what inheritance pattern does the skin condition most likely follow?

X-linked dominant (If the skin condition is caused by an X-linked dominant allele, a father would pass the allele on to all of his daughters, who would all have the skin condition. In contrast, the father would not pass the allele on to any of his sons because the sons would receive the father's Y chromosome, not his X chromosome. As a result, none of the sons would inherit the skin condition)

Females inherit one ________ from their father and one _______ from their mother

X; X

A sex-linked recessive allele produces a red-green color-blindness in humans. A normal woman named Kate whose father was color-blind marries a color blind man named William. What genotypes are possible for William's mother?

XAXa or XaXa

As the distance between two linked genes increases __________

the proportion of recombinant gametes increases, and the proportion of parental gametes decreases.

In mice, dwarfism is caused by an x-linked recessive allele, and a pink coat is caused by an autosomal dominant allele (coats are usually brown). If a dwarf female from a pure line is crossed with a pink male from a pure line, what are the parental genotypes?

XdXd;pp x XDY;PP We were told that they are pure breeding lines so we know that they have to have two of the same alleles for each loci

Males inherit their __________ from their father, so they MUST inherit their _________ from their mother

Y; X

A certain breed of parrot can produce two types of pigment in its feathers - blue and yellow. These pigments are controlled by two different genes that assort independently. For both of these genes, "produces pigment" is dominant and "doesn't produce pigment" is recessive. A bird that produces both yellow and blue pigment will have green feathers and a bird that produces neither pigment will have white feathers. In a dihybrid cross of two green parrots (Yy x Bb)... What genotypes are possible, and in what ratio?

YYBB 1/16 YYBb 2/16 YyBB 2/16 YyBb 4/16 YYbb 1/16 Yybb 2/16 yyBB 1/16 yyBb 2/16 yybb 1/16

In peas, the yellow allele is dominant over the green allele. If a plant with yellow peas is crossed to a plant with green peas, the resulting plants are 50% yellow and 50% green. What is the genotype of the parents in this cross?

Yy × yy

Pure-breeding

a homozygote for the alleles in question

When all individuals in a population are identical with regard to a particular trait, this is _________

a monomorphic trait

Polymorphic trait

a trait where you can have many common alleles in a population; 2 or more WILDTYPE alleles

Which of the following would be true of a plant heterozygous for a single gene controlling flower color? (Assume complete dominance). a) If crossed with another heterozygous plant, the majority of progeny will have the dominant flower color. b) It displays the recessive flower color. c) It will produce gametes with recessive flower color alleles and gametes with dominant flower color alleles in about a 3:1 ratio. d) About half of all its progeny will display the recessive flower color.

a) If crossed with another heterozygous plant, the majority of progeny will have the dominant flower color. (There will be roughly three times as many plants with the dominant flower color as plants with the recessive flower color.)

The expected ratio of phenotypes among the progeny of a test cross is 1:1:1:1. Out of 200 total resulting progeny, 48 occur in one of the four phenotypic classes. Given this information, which of the following must also be true? a) The value of observed - expected for this cell = -2. b) At least one additional cell must also contain a count of 48. c) Since 48 is so close to the expected value, there is no need to calculate chi square before drawing a conclusion about the ratio. d) The progeny of this cross do not conform to a 1:1:1:1ratio.

a) The value of observed - expected for this cell = -2.

Recessive

allele's phenotype only shown when 2 copies

Dominant

allele's phenotype shown with just one copy

Pleiotrophic allele

an allele that affects several properties of an organism.

What is a mutant allele?

any allele other than the wild type

A p value ≥ 0.05 means differences

are due to chance

You would like to know whether the progeny of a pair of mated fruit flies are distributed among the resulting four phenotypic classes in a 1:1:1:1 ratio. You perform a chi-square test and obtain a p value of 0.04. Assuming you have done the test correctly, select the best interpretation of this result. a) The traits being studied are on separate chromosomes. b) The differences between the observed and expected counts are too large to be attributed to chance. c) Approximately 4% of the offspring lie outside the range of values expected for a 1:1:1:1 ratio. d) The phenotypic ratio is actually 9:3:3:1

b) The differences between the observed and expected counts are too large to be attributed to chance. (It is on this basis (p< 0.05) that the decision to reject the hypothesis of a 1:1:1:1 ratio is made.)

Which of the following statements about autosomal recessive traits is true? a) If an individual expresses the trait, none of his or her offspring will express the trait. b) Only females can pass the trait to their offspring. c) If neither parent expresses the trait, but the offspring does, both parents must be heterozygous for the trait. d) If an individual expresses the trait, then all of his or her offspring will also express the trait.

c) If neither parent expresses the trait, but the offspring does, both parents must be heterozygous for the trait.

A couple is thinking about starting a family and is worried that they might both be carrying a recessive allele for sickle cell disease. They have a ________ test.

carrier

The blood type example is an example of what types of inheritance?

codominance and multiple alleles

How to get recombinant gametes when genes are linked?

crossing over

How to get recombinant gametes when genes are unlinked?

crossing over and/or independent assortment

Which of the following genotypes represents a gamete produced by a failure to segregate during meiosis in a cell of genotype AaBbCC? a) aBC b) ABC c) abC d) AaBC

d) AaBC

A patient has a muscular degenerative disease. A test is done to confirm what the physician thinks and a gene mutation is found in muscle-related gene. This was a _______ test.

diagnostic

A condition in which one gene pair masks the expression of a nonallelic gene pair is called ________.

epistasis

In a dihybrid cross, the Mendelian ratios are 9:3:3:1. Less than 4 phenotypic classes indicates:

gene interaction

Give an example of how a phenotype expression varies at one age relative to another within a single individual

gene products may play more essential roles at certain life stages, and it is likely that the internal physiological environment of an organism changes with age.

In rats, the following genotypes of two independently assorting autosomal genes determine coat color. A_B_ (gray) A_bb (yellow) aaB_ (black) aabb (cream) A third gene pair on a separate autosome determines whether or not any color will be produced. The CC and Cc genotypes allow color according to the expression of the A and B alleles. However, the cc genotype results in albino rats regardless of the A and B alleles present. What phenotypes will these genotypes produce? A_B_C_ A_B_cc A_bbC_ A_bbcc aaB_C_ aaB_cc aabbC_ aabbcc

gray, albino, yellow, albino, black, albino, cream, albino

Sickle cell anemia is caused by the recessive allele HbS. Heterozygotes are not anemic, but their cells are slightly sickled. In terms of sickle cell shape, the Hb alleles are...

incompletely dominant

Assume that a cross is made between AaBb and aabb plants and that the offspring fall into approximately equal numbers of the following groups: AaBb, Aabb, aaBb, aabb. These results are consistent with ________.

independent assortment

RF =/> 50 %:

independently assorting genes; either 2 genes are really far apart on one chromosome, or they are on different chromosomes

Dihybrid

involves two genes and the individual is heterozygous for each one

What is + on a complementation test?

it means that complementation has occurred and the wild type phenotype is restored; the two genes are not the same

A mutation in a gene often results in a reduction of the product of that gene. The term for this type of mutation is ________.

loss of function or null if it is a complete loss

Two processes are responsible for genetic variation:

meiotic recombination, which includes independent assortment and crossing over, and mutation

One type of gene interaction is epistasis, where one gene or gene pair __________ another gene or gene pair.

modifies or masks the expression of

Crosses in which F1 plants heterozygous for a given allele are crossed to generate a 3:1 phenotypic ratio in the F2 generation are known as

monohybrid cross

The presence of more than two alternative forms of a given gene would be called ________.

multiple alleles

If Jane and John want to have another child, they plan to see a genetic counselor to find out when it would be best to test for galactosemia. A newborn with galactosemia must be put on a lactose- and galactose-free diet as soon as possible after birth. Even on this diet, affected individuals may still suffer from learning disabilities, ovarian failure (in young women), late-onset cataracts, and early death. What type of screening should they do?

newborn screening (either assaying for the GALT enzyme or measuring excess galactose in the newborn's blood)

What is - on a complementation test?

no complementation has occurred; mutant phenotype offspring; the two genes are the same

Do the gene products have to physically interact in gene interaction?:

no, the cellular development of numerous gene products contributes to the development of a common phenotype; for example, the development of an eye is phenotypically determined by many different genes, some for size, color, shape, texture, etc.

A p value < 0.05 means differences are

not due to chance

Penetrance is often a (over/under) estimate?

overestimate

In mice, dwarfism is caused by an x-linked recessive allele, and a pink coat is caused by an autosomal dominant allele (coats are usually brown). If a dwarf female from a pure line is crossed with a pink male from a pure line, what will be the phenotypes of the F1 and the F2 progeny in each sex?

pink female, brown female, pink dwarf female, brown dwarf female, pink male, brown male, brown dwarf male, pink dwarf male

A patient is worried that she might have the breast cancer gene mutation that her mother and aunt had. She has a test to see if she has the mutation which will affect the probability of her getting breast cancer. This is a ________ test.

predictive

A couple has just gone through in vitro fertilization. Before implanting some of the embryos, they test the embryos and only implant ones that do not have cystic fibrosis. What type of test is this?

preimplantation test

A woman is pregnant and the physician suspects a bone growth disorder in the developing fetus. The physician orders a ________ test.

prenatal

Which term describes the individual in a pedigree whose phenotype was first brought to the attention of a medical researcher?

proband

Variable expressivity

range of expression of a given phenotype (the degree or intensity); all have the same genotype, but have a different degree of phenotype

Rules for x-linked dominant disorders

rare male and females affected does not skip generations never have father to son transmission An affected male passes to ALL his daughters

What does the semi-colon indicate? A/a;B/b

separate chromosomes...independent assortment

What is meant by the term gene interaction?

several genes influence a particular characteristic; phenotypic characteristics can be influenced by the interactions of many different genes and their products

Define wildtype allele in a population

the allele that occurs most frequently in the population...the "normal" allele

Genotype

the allelic or genetic constitution of an organism

Recombination frequency for two genes (RF) is proportional to:

the length of physical DNA between them on a chromosome

In rats, the following genotypes of two independently assorting autosomal genes determine coat color. A_B_ (gray) A_bb (yellow) aaB_ (black) aabb (cream) A third gene pair on a separate autosome determines whether or not any color will be produced. The CC and Cc genotypes allow color according to the expression of the A and B alleles. However, the cc genotype results in albino rats regardless of the A and B alleles present. For the following cross, what fraction of the offspring would you expect to have each genotype? AAbbCC x aaBBcc A_B_C_ A_B_cc A_bbC_ A_bbcc aaB_C_ aaB_cc aabbC_ aabbcc

they will all be A_B_C

Why would a scientist do a complementation analysis? Give an example with fruit fly wings

to see, because we know many genes are involved in producing a phenotype, if two different organisms with a similar phenotype due to a recessive mutation have the same mutant alleles in the same genes. To do this, we will cross 2 mutant strains and analyze the F1 generation. • Outcome 1: All offspring have normal wings o The two RECESSIVE mutations are in separate genes and are not alleles of one another. The F1 flies are heterozygous for both genes o This is complementation • Outcome 2: All offspring fail to develop wings o The 2 mutations are of the same gene and they are alleles of one another o This is not complementation

A dihybrid was crossed to a tester (dg/dg). The result of the cross was: 40% Dg/dg; 40% dG/dg; 10% DG/dg and 10% dg/dg. Based on the genotypic frequencies of offspring from this cross, can you tell if the dihybrid was a cis or a trans dihybrid?

trans dihybrid

It is 1965, before diagnostic genetic tests could be performed for Taysach's disease, an autosomal recessive disorder. A husband and wife each had an uncle that died from Taysach's disease. The couple's first child died from Taysach's. They really want a second child but they are scared. What do you tell them in this second visit about their chances of a second child having Taysach's?

we now know that both of the parents are carriers, so now the probability is ¼

Heterozygote

when alleles are different

Homozygote

when both alleles are the same

Complementation analysis is used to determine __________.

whether two mutations that produce the same phenotype reside in the same or different genes. If the mutations reside in different genes, when the two mutants are crossed the offspring should be wild type for that trait. If the two mutations reside in the same gene, only mutant offspring will be obtained in a cross.