Exam 1
malesor femlaes? Cannot be heterozygous for X-linked genes..
Males
what is a test cross?
it is used to determine the genotype of an individual that expresses a dominant trait
How many different kinds of gametes will be expected by an individual with the genotype PpCcTTRr?
8
What is the phenotypic ratio of a dihybrid cross?
9:3:3:1
What types of ratios are likely to occur in crosses (F2) when one is dealing with two interacting, epistatic gene pairs?
9:7, 9:3:4, 12:3:1, 15:1
A bacteriophage that is capable of entering either a lytic or lysogenic cycle is called a(an) A. temperate bacteriophage. B. virulent bacteriophage. C. plasmid. D. episome. E. plaque-forming unit.
A
A situation in which there are more than two alternative forms of a given gene is called ________. A. multiple alleles B. alternation of generations C. codominance D. incomplete dominance E. hemizygosity
A
Bacteriophages engage in two interactive cycles with bacteria. What are these cycles? A. lytic and lysogenic B. insertion and replication C. auxotrophic and prototrophic D. heteroduplex and homoduplex E. negative and positive
A
Hemizygosity would most likely be associated with which of the following? A. codominance B. incomplete dominance C. trihybrid crosses D. X-linked inheritance E. sex-limited inheritance
D
What is the genotypic ratio of the F2 generation in a test cross?
If the tall plant is Heterozygous then the test cross will give an equal number of tall and dwarf plants (a 1:1 ratio)
Which allele is dominant in incomplete dominance?
neither allele is dominant, so phenotypic ratio is identical to genotypic ratio
What is dominant epistasis?
occurs when a dominant allele at one locus masks the expression of the alleles at a second locus.
where are genes located?
on the chromosome
The two traits inherited in a dihybrid cross are inherited independently A. True B False
A. True
Albinism, lack of pigmentation in humans, results from an autosomal recessive gene (a). Two parents with normal pigmentation have an albino child. (a) What is the probability that their next child will be albino? (b) What is the probability that their next child will be an albino girl? (c) What is the probability that their next three children will be albino?
(a) 1/4 (b) 1/4 X 1/2 = 1/8 (c) 1/4 X 1/4 X 1/4 = 1/64
In the mouse, gene A allows pigmentation to be deposited in the individual coat hairs, while its allele a prevents such deposition of pigment, resulting in an albino. Gene B gives agouti (wild-type fur), while its allele b gives black fur. (a) Diagram the cross between a doubly heterozygous agouti mouse mated with a doubly homozygous recessive white mouse. (b) What would be the expected phenotypic ratio in the progeny?
(a) AaBb X aabb (b) 1 (agouti): 1 (black): 2 (albino)
Comb shape in chickens represents one of the classic examples of gene interaction. Two gene pairs interact to influence the shape of the comb. The genes for rose comb (R) and pea comb (P) together produce walnut comb. The fully homozygous recessive condition (rrpp) produces the single comb. Assume that a rose comb chicken is crossed with a walnut comb chicken and the following offspring are produced: 17 walnut, 16 rose, 7 pea, 6 single. (a) What are the probable genotypes of the parents? (b) Give the genotypes of each of the offspring classes.
(a) Rrpp X RrPp (b) R-Pp (walnut) R-pp (rose) rrPp (pea) rrpp (single)
A cross was made between homozygous wild-type female Drosophila and yellow-bodied male Drosophila. All of the resulting offspring were phenotypically wild-type. Offspring of the F2 generation had the following phenotypes: Sex Phenotype Number male wild 96 male yellow 99 female wild 197 Based on this information: (a) Is the mutant gene for yellow body behaving as a recessive or a dominant? (b) Is the yellow locus on an autosome or on the X chromosome?
(a) recessive (b) X-linked
In peas, gray seed color is dominant to white. For the purposes of this question, assume that Mendel crossed plants with gray seeds with each other and the following progeny were produced: 320 gray and 80 white. (a) What is the most probable genotype of each parent? (b) What genotypic and phenotypic ratios are expected in the progeny of such a cross?
(a) using the symbols G = gray and g = white, Gg X Gg (b) genotypic = 1:2:1, phenotypic = 3:1
The enzyme glucose-6-phosphate dehydrogenase deficiency (G6PD) is inherited as a recessive gene on the X chromosome in humans. A phenotypically normal woman (whose father had G6PD) is married to a normal man. (a) What fraction of their sons would be expected to have G6PD? (b) If the husband had G6PD, would it make a difference to your answer in part (a)?
(a) ½ (b) no
What are two different types of alleles that alter phenotype and what are their differences?
+Wild Type+ -Occurs most frequently in a population -Usually dominant -Gene product (i.e. - protein) is functional -Wild type phenotype -Mutant Allele- -Modified genetic material -May produce altered gene product (i.e. - protein) -May affect protein function
What is an allele?
-Alternative forms of a gene --Phenotype is determined by which form (alleles) of a gene are present in an organism --Tall and Dwarf phenotypes are determined by different alleles of the same gene
How do you distinguish between codominance and incomplete dominance?
-Codominance inheritance is characterized by distinct expression of the gene products of both the alleles. Both alleles produce a similar, but distinct product that are both functional -Not a blended phenotype like incomplete dominance - Neither allele is dominant to the other - No Intermediate phenotype
If two independently isolated mutations cause the same phenotype, how can you determine if the mutations occur in the same or in different genes?
-Complementation Analysis: Cross the two mutant strains --Two possible outcomes depending on whether the mutations are in the same gene or different genes --Mutations that are present in a single gene belong to the same complementation group. -If the mutations are alleles of the same gene no complementation occurs. Because the mutations are in the same gene, offspring are all homozygous recessive and no wings develop.
How does the crossing of two white pea plants give rise to a 9:7 ratio of purple to white plants?
-Cross between White-flowered pea plants --All F1 plants are purple and F2 occurs in ratio of 9 purple to 7 white --The plant needs to be homozygous recessive at at least one of two alleles to have white flowers -All cases of the modified Dihybrid ratios have two things in common: --Principles of segregation and independent assortment are still followed --F2 ratios are expressed in 16ths-suggests two gene pairs are involved
What are the results of independent assortment?
-Each gamete receives 1 member of every pair of unit factors -One pair does not influence the segregation of any other pair -All possible combinations of gametes are formed with equal frequency
what is Co-dominance?
-Expression of both alleles is equal and equally expressed -Where two alleles of a single gene produce two fully functional but distinct products.
what does hypostatic mean?
-Gene X could encode a transcription factor necessary for expression of the Y gene. The Y gene is hypostatic to X and X is epistatic to Y -Y depends on X for its expression
Example of a Dominant Lethal Allele?
-Huntington Disease-caused by autosomal dominant allele (H) --Heterozygotes- Hh -carry the dominant lethal allele --Onset of disease symptoms delayed into adulthood --Allows the mutant allele to be passed on to next generation, but affected individuals must reproduce before lethal allele is expressed. --These dominant alleles die early in life but ARE born, don't realize its passed on until after reproduction --One copy needed to be lethal..1:2 chance in passing this to offspring
Explain an h subtstance
-If H substance is incompletely formed then the sugars to produce either the A or B antigen cannot be added -This results in a person having type O blood even though they have either the IA and/or IB alleles -Caused by a recessive mutation in a different gene (designated h) -If h subtance does not function properly and isnt made properly, you cant add the next part (antigen) Which makes you O because you cant attach the antigens to your blood groups
what is the bombay phenotype?
-Individual can be genotypically IA and/or IB, but phenotypically IO -Occurs if they are deficient in an enzyme that allows the A or B sugar molecules to be added -Homozygous recessive condition at one locus that masks expression at a second locus hh masks the expression of the IA and IB alleles
what is gene interaction?
-Many characteristics are under the control of several genes -The products of different genes contribute to the development of a phenotype
what are two things mutations affect?
-Mutations in genes produce new alleles - can lead to a change in phenotype -Mutations alter the function of the gene product
What are Complementation Groups useful for?
-Mutations that are present in a single gene belong to the same complementation group. -Useful for studying mutations that affect the same trait -Possible to predict the number of genes involved in determining that trait
Give an example of recessive epistasis
-Normal mouse coat color is agouti (A) -Mice that are AA or Aa are agouti -Mice that are aa are black -Albino mice: due to a recessive mutation at a second locus -bb mice are albino -Genotype at agouti locus does not matter when bb is present -AAbb; Aabb, and aabb mice are albino -F1 Cross: AaBb x AaBb Genotypic Ratio = 9:3:3:1 Phenotypic Ratio = 9:3:4 Precursor-->Black Pigment-->Agouti Albino-->Black Pigment-->Agouti bb genotype suppresses (masks) expression of the A gene (follow biochemical pathway)
what is epistasis?
-Occurs when the expression of one gene or gene pair masks or modifies the expression of another gene or gene pair -Homozygous recessive allele at one locus (X) prevents expression of the alleles at a second locus (Y)
How do you perform a Monohybrid Cross?
-Single cross -Two plants with contrasting traits (tall vs dwarf) -Features are always contrasting, NO MIXING
What is a dihybrid cross?
-Two-factor cross --Simultaneously exam two pairs of contrasting traits -Example: Pea plants with yellow and round seeds crossed with pea plants with green and wrinkled seeds
What are Mendel's first three Postulates?
-Unit factors exist in pairs (TT, Tt, tt) -Dominance and Recessivness -Segregation of unit factors during gamete formation (paired ones segregate randomly)
what is incomplete(partial) dominance?
-Where a cross between parents with contrasting traits results in an offspring with an intermediate phenotype e.g. - Flower color in snapdragon - One functional gene does not give the full red color -Heterozygotes in F2 have pink color & all progeny in F1 generation
What type of parent is used in a test cross? and Why?
-a recessive (heterozygous) parent -To determine the genotype of the F2 generation --50% progeny then you know the genetic f2 is heterozygous --no appearance of dwarf the genetic makeup was pure homozygous and dominant
What can effect mendelian ratios?
-alleles that alter the phenotype
what is penetrance?
-percentage of individuals that show at least some degree of expression of a mutant genotype --e.g. - if 20% of mutant individuals show a wild-type like appearance then the mutant gene had an 80% penetrance
In a monohybrid cross, what happens when going from P1, to F1, to F2?
-the P1 generation will be true breeding -the F1 generation is controlled by the dominant unit factor..which means it will then hide one of the traits from the P1's (making it heterozygous) -the original traits will show up in the F2 generation in a 3:1 ratio
what is needed to perform a test cross in a dihybrid cross?
-the phenotype-If you know the phenotype, you can determine the genotype by performing crosses to a homozygous recessive plant (ggww) -The following genotypes all have a yellow; round phenotype: GGWW GGWw GgWW GgWw -When crossing ggww with all the yellow round genotypes you will always get GW
If a ratio is expressed in 16ths..
...it indicates that two genes are involved and are interacting during expression of the phenotype
Assuming independent assortment, what proportion of the offspring of the cross AaBbCcDd X AabbCCdd will have the aabbccdd genotype?
0
In a mating between individuals with the genotypes IAIB X IOIO, what percentage of the offspring are expected to have the O blood type?
0
Two forms of hemophilia are determined by genes on the X chromosome in humans. Assume that a phenotypically normal woman whose father had hemophilia is married to a normal man. What is the probability that their first son will have hemophilia?
1/2
Albinism, lack of pigmentation in humans, results from an autosomal recessive gene (a). Two parents with normal pigmentation have an albino child. What is the probability that their next child will be an albino girl?
1/4 X 1/2 = 1/8
What is the genotypic ratio in a monohybrid cross for the F2 generation?
1:2:1 (TT, Tt, Tt, tt)
Assume that a dihybrid cross (AaBb X AaBb) is made in which the gene loci are autosomal, independently assorting, and incompletely dominant. What phenotypic ratio would you expect from such a cross? Provide just the ratio, not the phenotypes.
1:2:1:2:4:2:1:2:1
A particular cross gives a modified dihybrid ratio of 9:7. What phenotypic ratio would you expect in a testcross of the fully heterozygous F1 crossed with the fully recessive type? Diagram the testcross using A,a,B,b as symbol sets.
1:3 AaBb X aabb > AaBb, Aabb, aaBb, aabb
How do you solve for possible gamete combinations in a dihybrid cross?
2^haploid number
The following F2 results occur from a typical dihybrid cross: purple: A_B_ 9/16 white: aaB_ 3/16 white: A_bb 3/16 white: aabb 1/16 If a double heterozygote (AaBb) is crossed with a fully recessive organism (aabb), what phenotypic ratio is expected in the offspring?
3 (white):1 (purple)
Name the individual whose work in the mid-1800s contributed to our understanding of the particulate nature of inheritance as well as the basic genetic transmission patterns. With what organism did this person work? A. Gregor Mendel, Pisum sativum B. George Beadle, Neurospora C. Thomas Hunt Morgan, Drosophila (fruit fly) D. Calvin Bridges, Drosophila (fruit fly) E. Boris Ephrussi, Ephestia
A
The fundamental Mendelian process that involves the separation of contrasting genetic elements at the same locus is called A. segregation. B. independent assortment. C. continuous variation. D. discontinuous variation. E. dominance or recessiveness.
A
How many different types of gametes can be formed by the genotype DdEeFF ? and WHY?
Answer: 4 Explanation: -The first two loci are heterozygous and have different segregating alleles, whereas only one allele is possible for the third locus. -Therefore the possible number of gametes is 2 x 2 x 1. -The formula 2n could be used to determine the number of -gametes, where n = the number of heterozygous traits. -The possible gametes are DEF, dEF, DeF, and deF.
How does an auxotroph differ from a prototroph?
Auxotrophs have lost, through mutation, the ability to grow on minimal medium.
A condition in which one gene pair masks the expression of a nonallelic gene pair is called ________. A. codominance B. epistasis C. dominance D. recessiveness E. additive alleles
B
A recessive allele in tigers causes the white tiger. If two normally pigmented tigers are mated and produce a white offspring, what percentage of their remaining offspring would be expected to have normal pigmentation? A. 50% B. 75% C. about 66% D. about 90% E. 25%
B
What types of phenotypic ratios are likely to occur in crosses when dealing with a single gene pair where all the genotypic combinations are of equal viability? A. 9:3:3:1, 27:9:9:9:3:3:3:1 B. 1:2:1, 3:1 C. 1:4:6:4:1, 1:1:1:1 D. 12:3:1, 9:7 E. 2:3, 1:2
B
Monohybrid crosses are sex dependent A. True B. False
B. False
What is a null mutant allele?
Complete loss of function - usually no protein is produced
How can the genotype of an F2 generation be determined?
By running a test cross
Name two forms of recombination in bacteria. A. lytic and lysogenic B. auxotrophic and prototrophic C. conjugation and transduction D. mixed and generalized E. insertion and replication
C
Jacob, Wollman, and others developed a linkage map of E. coli that is based on time. What form of recombination is involved in generating a linkage map based on time?
Conjugation: An Hfr bacterium conjugating with an F- strain allows one to generate a map that is dependent on the passage of the donor chromosome across a conjugation tube.
Determine the probability that a plant of genotype CcWw will be produced from parental plants of genotypes CcWw and Ccww
Cc X Cc ---> 1/4 CC: 1/2 Cc: 1/4 cc Ww X ww--------> 1/2 Ww: 1/2 ww p of CcWw=(1/2 Cc)(1/2 Ww)=1/4 CcWw
Distinguish between F+ and F- bacteria.
F+ bacteria contain an F factor or plasmid that is capable of initiating conjugation.
Name the general category into which double-stranded circular extrachromosomal DNA elements such as F factors, ColE1, and R fall. A. capsid B. r-determinant C. plaque D. partial diploid E. plasmid
E
Explain the blood types
Four phenotypes exist A, B, AB, and O IA produces the A antigen IB produces the B antigen IAIB produces both A and B antigens IO does not produce either antigen IA and IB are dominant to IO, but codominant to each other
Explain how recessive lethal alleles are bad.
Heterozygotes have yellow coats, mutant allele is dominant AYA - AY is dominant with respect to coat color, phenotype AYAY Homozygotes die early in development (before birth - Embryonic Lethal) AY is recessive with respect to lethality A AY x A AY - instead of 1:2:1 gives a 2:1 ratio since the AYAY are never born
What are some factors that affect the 3:1 monohybrid ratios? And also affect the predicted dihybrid ratios?
Incomplete dominance Codominance Multiple alleles Lethal alleles
Whats is Mendel's Fourth Postulate?
Independent Assortment- Segregation of any pair of unit factors occurs independently of all others
What is the difference genotypically between a loss of function allele and a gain of function allele?
Loss function-recessive Gain of function-dominant
What is a Loss of Function mutant allele?
Mutation results in a protein that reduces or eliminates the function of the protein
what is Complementary Gene Interaction?
Need at least one wild type allele of each gene pair to produce the final product. Product of the two genes interact to influence the development of a common phenotype
what is expressivity?
Range of expression of a gene (e.g.- eyeless in Drosophila) Normal eyes to partial reduction in eye size to complete absence of eyes
one wild-type copy is enough for the organism to survive, but two copies of the mutant allele is lethal
Recessive lethal
What is a proband?
The individual whose phenotype first brought attention to the investigation and construction of the pedigree
What are the roles of the recBCD genes?
They function in bacterial recombination.
What is the product law of probabilities?
When 2 independent events occur simultaneously (e.g.-inheritance of C or c and W or w), the combined probability of the two outcomes is equal to the product of their individual probabilities of occurence
What are multiple alleles?
Where there are more than two alleles of a single locus that produce fully functional but distinct products
what is hemizygous?
Y acts as homolog to X during meiosis, but contains genes that are not found on X and genes on X are not on Y -half the compliment of the gene
what is a true breeding organism?
an organism that always passes down certain phenotypic traits (i.e. physically expressed traits) to its offspring.
What did Sutton and Boveri Think Mendel's unit factors were?
chromosomes rather than genes- Chromosomal theory of inheritance
Under what conditions does one expect a 9:3:3:1 ratio?
dihybrid cross (F2) with independently assorting, completely dominant genes
The white-eye gene in Drosophila is recessive and sex-linked. Assume that a white-eyed female is mated to a wild-type male. What would be the phenotypes of the offspring?
females wild-type, males white-eyed
Regarding the ABO blood group system in humans, if an individual is genetically IBIO and yet expresses the O blood type, it is likely that that individual has the _______ genotype.
hh (Bombay)
who do you get your mitochondria from?
mom
What is a gain of function mutant allele?
mutation that enhances the function of the protein product
In studies of human genetics, usually a single individual brings the condition to the attention of a scientist or physician. When pedigrees are developed to illustrate transmission of the trait, what term does one use to refer to this individual?
proband
What is a silent mutation mutant allele?
they do not alter the phenotype, but the genotype is changed
"Gain-of-function" mutations are generally dominant since one copy in a diploid organism is sufficient to alter the normal phenotype.
true
A typical epistatic ratio is 9:3:4.
true
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
Assuming complete dominance, a 3:1 phenotypic ratio is expected from a monohybrid sib or self-cross.
true
To test Mendel's law of independent assortment, the experimenter needs a minimum of two different genes and their two alleles.
true
To test Mendel's law of segregation, the experimenter needs a minimum of two contrasting forms of a gene.
true
Can a dominant mutation override a wild type allele?
yes
