Genetics: Chapter 3

What term describes an individual possessing two of the same alleles at a gene locus?

homozygous

What information can the chi‑square goodness‑of‑fit test provide?

how well the observed results of a genetic cross fit the expected values

Select the conclusions that are indicated by this experiment regarding the validity of the pangenesis and the germ‑plasm theories discussed in Chapter 1.

- The production of black guinea pig offspring suggests that the allele for black coat color was passed along to the offspring from the transplanted ovary, thus supporting the germ‑plasm theory. - Because no white guinea pigs were produced, no white coat alleles traveled to the ovary and into the gametes of the white female, thus indicating pangenesis did not occur.

Suppose there is a vial containing a single generation of flies from a cross. There is an interesting phenotype where many individuals have abnormally long hairlike bristles, sensory organs extending from the dorsal thorax, as opposed to the short wirelike wild‑type bristles among the other siblings. References state that this mutant has a dominant mutation called Suave (Su) and that the phenotype of flies that are heterozygous or homozygous for Su appear phenotypically identical. Which fly should be crossed to a Suave male from this vial in order to generate progeny that help determine the male's genotype?

a wild‑type female sibling

Which of the statements can be concluded from Gregor Mendel's experiments with pea plants?

- Alleles of different genes are inherited independently of each other. - Only one allele determines the phenotype in heterozygous individuals.

Imagine that two unlinked autosomal genes with simple dominance code in goats for size, where L is large and l is small, and for color, where R is red and r is tan. If a small, tan male goat mates with a large, red female goat of an unknown genotype, what is the probability that they would produce small, tan offspring? probability:

0.0625

If an Aa individual is crossed to an aa individual, what will be the phenotypic ratio in the offspring?

1:1

The principle of independent assortment involves at least how many different gene pairs?

2

In pea plants, the allele for round seed shape, R, is completely dominant to the allele for wrinkled seed shape, r. Complete the Punnett square showing the genotypes possible among the offspring when two heterozygous individuals are crossed. Use the information from the Punnett square to answer the second question. In this cross between two heterozygous pea plants, what are the chances that an offspring with wrinkled seeds will be produced?

25% ___| R. | r. | ----------------------- R. | RR | Rr | ----------------------- r. | Rr | rr |

In humans, oculocutaneous (OCA) albinism is a collection of autosomal recessive disorders characterized by an absence of the pigment melanin in skin, hair, and eyes. That is, normal pigmentation (𝐴)(A) is dominant over albino characteristics (𝑎)(a) . For this question, assume the phenotype is determined by a single gene with two alleles. If both parents have normal pigmentation, what are all of the possible genotypes that may be observed in their offspring?

AA, Aa, or aa

A cross between an AABB individual and an aabb individual will produce what type of offspring?

All will be AaBb.

How did Mendel use self‑pollination and cross‑pollination techniques in his experiments with flower color to observe the basic patterns of inheritance?

By cross‑pollinating a parental generation of plants with different‑colored flowers and allowing the F1 generation to self‑pollinate, Mendel observed the basic patterns of inheritance in the F2 generation.

At the end of your biology class, your professor asks you to develop a project to determine the genotype of a plant with red flowers. Red petal color (R) is dominant to pink flower color (r). To accomplish this task, you cross the plant with the unknown genotype with heterozygous red‑flowered plants. A partially filled Punnett square is provided. Rr?? Which ratios are valid predictions of flower colors in the offspring?

- all red flowers - 3 red : 1 pink flowers

Suppose that goats have one gene that codes for color, where A is brown and a is white. The goats also have another gene that codes for height, where B is tall and b is short. If these two genes are unlinked, what is the probability that a cross between Aa Bb × Aa bb parents will produce three out of five offspring that are white and tall? Enter your answer as a decimal, rather than as a percentage. probability:

0.015

In mice, an allele for apricot eyes (a) is recessive to an allele for brown eyes (a+). At an independently assorting locus, an allele for tan (t) coat color is recessive to an allele for black (t+) coat color. A mouse that is homozygous for brown eyes and black coat color is crossed with a mouse having apricot eyes and a tan coat. The resulting F1 are intercrossed to produce the F2. In a litter of eight F2 mice, what is the probability that exactly two will have apricot eyes and tan coats? Use three decimal places for the answer. probability:

0.074

What will be the genotypic ratio in the offspring of two Aa parents that are crossed with each other?

1 : 2 : 1

Step 5: Calculate the combined probability of Aa Bb Cc Dd. For the offspring genotype Aa Bb Cc Dd enter the proportions you calculated for each locus. Then, calculate the combined proportion among the offspring. Use decimals (e.g., 0.5) rather than fractions to do your calculations. 1) probability of Aa among offspring: 2) probability of Bb among offspring: 3) probability of Cc among offspring: 4) probability of Dd among offspring: 5) combined probability of Aa Bb Cc Dd =

1) 0.5 2) 0.5 3) 0.5 4) 0.5 5) 0.5 x 0.5 x 0.5 x 0.5 = 0.0625

Suppose a man is heterozygous for heterochromia, an autosomal dominant disorder which causes two different‑colored eyes in an individual, produced 25‑offspring with his normal‑eyed wife. Of their children, 1616 were heterochromatic and 99 were‑normal. Calculate the chi‑square value for this observation. 1) 𝜒2= 2) Identify the statement that best interprets the results of the chi‑square analysis. Refer to the chi‑square distribution table to identify the statement that best interprets the chi‑square results.

1) 1.96 2) It is not unusal that a heterozygous man produced 16 out of 25 offspring with heterochromia.

Phenylketonuria (PKU) is a disease that results from a recessive gene. Two normal parents produce a child with PKU. 1) What is the probability that a sperm from the father will contain the PKU allele? 2) What is the probability that an egg from the mother will contain the PKU allele? 3) What is the probability that their next child will have PKU? 4) What is the probability that their next child will be heterozygous for the PKU gene?

1) 1/2 2) 1/2 3) 1/4 4) 1/2

Suppose two parents, a father with the genotype AaBbCcDdee and a mother with the genotype aaBbCCDdEe, want to have children. Assume each locus follows Mendelian inheritance patterns for dominance. What proportion of the offspring will have each of the specified characteristics? Round your answers to two decimal places. 1) same genotype as the father: 2) same genotype as the mother: 3) phenotypically resemble the father: 4) phenotypically resemble the mother: 5) phenotypically resemble neither parent:

1) 1/32 = 0.03 2) 1/32 = 0.03 3) 9/64 = 0.14 4) 9/64 = 0.14 5) 46/64 = 0.72

Now you can use the step by step method to answer this challenging question. Give the proportion of the progeny of this cross that are expected to have each of the following genotypes. Please answer as a decimal. 1) Aa Bb Cc Dd 2) aa bb CC dd 3) Aa bb Cc DD

1) 4/64 = 0.0625 2) 1/64 = 0.0156 3) 2/64 = 0.031

Huntington's disease is an inherited autosomal dominant disorder that can affect both men and women. Imagine a couple has had seven children, and later in life, the husband develops Huntington's disease. He is tested and it is discovered he is heterozygous for the disease allele, Hh. The wife is also genetically tested for the Huntington's disease allele, and her test results show she is unaffected, hh. 1) What is the percent probability that the first child of this couple will have Huntington's disease? 2) What is the probability that two of the seven children will have Huntington's disease?

1) 50% 2) 16.41%

In watermelons, bitter fruit (B) is dominant over sweet fruit (b), and yellow spots (S) are dominant over no spots (s). The genes for these two characteristics assort independently. A homozygous plant that has bitter fruit and yellow spots is crossed with a homozygous plant that has sweet fruit and no spots. The F1 are intercrossed to produce the F2. 1) What will be the phenotypic ratio in the F2? 2) If an F1 plant is backcrossed with the bitter, yellow‑spotted parent, what phenotypes and proportions are expected in the offspring? 3) If an F1 plant is backcrossed with the sweet, nonspotted parent, what phenotypes and proportions are expected in the offspring?

1) 9/16 bitter fruit, yellow spots; 3/16 bitter fruit, no spots; 3/16 sweet fruit, yellow spots; and 1/16 sweet fruit, no spots 2) All bitter fruit with yellow spots. Genotype ratio 1:1:1:1. No phenotype ratio. 3) 1/4 bitter fruit, yellow spots; 1/4 bitter fruit, no spots; 1/4 sweet fruit, yellow spots; and 1/4 sweet fruit, no spots

Step 1: Determine the parental genotypes and proportion of offspring genotypes for locus 1. 1) What are the genotypes of the parents with respect to locus 1 (i.e., alleles A and a)? 2) What are the genotype probabilities among the offspring with respect to locus 1 (i.e., alleles A and a)?

1) Aa × Aa 2)1/4 AA, 1/2 Aa, and 1/4 aa

Step 2: Determine the parental genotypes and proportion of offspring genotypes for locus 2. 1) What are the genotypes of the parents with respect to locus 2 (i.e., alleles B and b)? 2) What are the genotype probabilities among the offspring with respect to locus 2 (i.e., alleles B and b):

1) Bb × bb 2) 1/2 Bb and 1/2 bb

Step 3: Determine the parental genotypes and proportion of offspring genotypes for locus 3. 1) What are the genotypes of the parents with respect to locus 3 (i.e., alleles C and c)? 2) What are the genotype probabilities among the offspring with respect to locus 3 (i.e., alleles C and c)?

1) CC × Cc 2) 1/2 CC and 1/2 Cc

Step 4: Determine the parental genotypes and proportion of offspring genotypes for locus 4. 1) What are the genotypes of the parents with respect to locus 4 (i.e., alleles D and d)? 2) What are the genotype probabilities among the offspring with respect to locus 4 (i.e., alleles D/d):

1)Dd × Dd 2) 1/4 DD, 1/2 Dd, and 1/4 dd

In pea plants, plant height is controlled by a single autosomal dominant gene. Tall plants (H) are dominant to short plants (h). In a cross of two tall heterozygous plants, which phenotype ratio is expected from the resulting offspring?

3:1

Of the following ideas postulated by Gregor Mendel, which one requires at least two genes to be demonstrated?

Genes assort independently in humans.

In fruit flies, gray bodies (G) are dominant over black bodies (g), and red eyes (R) are dominant over orange eyes (r). Each individual possesses two alleles for each trait. If a fly that is homozygous dominant for both traits is crossed with a fly that is homozygous recessive for both traits, what is the predicted genotype of the offspring?

GgRr

Which organism did Gregor Mendel use to discover the basic principles of genetics?

Pisum sativum (pea plant)

What is a shorthand method for predicting outcomes of genetic crosses?

Punnett square

Use the image to observe the results of a cross between a tall pea plant and a short pea plant. What phenotypes and proportions will be produced for the two crosses?

Question 12

Suppose that two parents are both heterozygous for sickle cell anemia, which is an autosomal recessive disease. They have eight children. Use the binomial theorem to determine the probability that three of the children have sickle cell anemia and five of the children are healthy. Round your answer to the nearest tenth. probability:

Question 16

In cats, curled ears result from an allele, Cu, that is dominant over an allele, cu, for normal ears. Black color results from an independently assorting allele, G, that is dominant over an allele for gray, g. A gray cat homozygous for curled ears is mated with a homozygous black cat with normal ears. All the F1 cats are black and have curled ears. What phenotypes and proportions are expected from the two crosses?

Question 20

Horse coat color is controlled by many genes, including extension and cream. The extensions gene, E, determines pigment color. E−, representing either Ee or EE, produces a bay coat, and ee produces a red coat. The cream gene, Cr, is incomplete dominant and functions by decreasing the intensity of the E color phenotype. The crcr genotype does not alter the red or bay phenotype. However, the Crcr genotype changes red into palomino and bay into buckskin. This is called a single dilute. The CrCr genotype alters red into cremello and bay into perlino. This is called a double dilute. Suppose two buckskin horses, each with the Ee Crcr genotype, are crossed. Use the forked‑line (branched diagram) method to determine the proportion of each phenotype and each genotype in the next generation. Each proportion may be used more than once or not at all.

Question 21

Imagine that a scientist studies two traits in peas. The scientist noticed that round is dominant over wrinkled with regard to pea shape. Additionally, yellow is dominant over green with regard to pea color. To determine if these traits are linked, two individuals that are heterozygous for both traits were crossed. The data in the table represent the number of offspring produced by this dybrid cross. Phenotypic ratios represents the predicted proportion of offspring with each set of traits that would be produced if the traits independently assort. What can be determined about these traits based on Chi-square analysis?

Question 25

Pink eye and albinism are two recessive traits found in the deer mouse, Peromyscus maniculatus. In mice with pink eye, the eye is devoid of color and appears pink from the blood vessels within it. Albino mice are completely lacking color both in their fur and in their eyes. F. H. Clark crossed pink‑eyed mice with albino mice; the resulting F1 had normal coloration in their fur and eyes. He then crossed these F1 mice with mice that were pink‑eyed and albino and obtained the mice shown in the table below. It is very hard to distinguish between mice that are albino and mice that are both pink‑eyed and albino, so he combined these two phenotypic classes (F. H. Clark, 1936, Journal of Heredity 27:259−260). Match the expected numbers of progeny with each phenotype if the genes for pink‑eye and albinism assort independently. Use a chi‑square test to determine if the observed numbers of progeny fit the number expected with independent assortment. χ2=

Question 26

Alleles A and a are located on a pair of metacentric chromosomes. Alleles B and b are located on a pair of acrocentric chromosomes. A cross is made between individuals having the genotypes Aa Bb and aa bb. Label the gametes of the aa bb parent with the chromosomes carrying the correct alleles.

Question 6

If a plant has a genotype of Aa, we would assume which is true?

The A allele is dominant to the a allele.

When Mendel crossed a plant homozygous for round seeds to another plant homozygous for wrinkled seeds, he found that all the progeny had round seeds. How is this explained?

The allele for round seeds is dominant to the allele for wrinkled seeds.

White (w) coat color in guinea pigs is recessive to black (W). In 1909, W. E. Castle and J. C. Phillips transplanted an ovary from a black guinea pig into a white female whose ovaries had been removed. They then mated this white female with a white male. All the offspring from the mating were black in color (W. E. Castle and J. C. Phillips, 1909, Science 30:312-313). Which statement explains the results of this cross?

The color of the offspring was determined by genes in the transplanted ovary, not the genes of the female who gave birth.

A geneticist discovers an obese mouse in his laboratory colony. He breeds this obese mouse with a normal mouse. All the F1 mice from this cross are normal in size. When he interbreeds two F1 mice, eight of the F2 mice are normal in size and two are obese.The geneticist then intercrosses two of his obese mice, and he finds that all of the progeny from this cross are obese. These results lead the geneticist to conclude that obesity in mice results from a recessive allele. A second geneticist at a different university also discovers an obese mouse in her laboratory colony. She carries out the same crosses as the first geneticist and obtains the same results. She also concludes that obesity in mice results from a recessive allele. One day, the two geneticists meet at a genetics conference, learn of each others experiments, and decide to exchange mice. They both find that, when they cross two obese mice from the different laboratories, all the offspring are normal. However, when they cross two obese mice from the same laboratory, all the offspring are obese. Which option best explains their results?

The two obesity alleles are recessive to the wild-type alleles but are located at different loci.

How is a true breeding purple‑flowered pea plant different from a hybrid purple‑flowered pea plant?

They have the same phenotype but different genotypes.

Select the genotype of the offspring from this cross.

Ww

What value represents the number of ways in which the expected classes are free to vary in the chi‑square goodness‑of‑fit test?

degrees of freedom

What is a cross that occurs between two individuals that differ in two characteristics?

dihybrid cross

Mendel's principle of segregation can be explained by what process?

meiosis

What is the physical appearance or manifestation of a characteristic called in genetics?

phenotype

An individual possesses two alleles at a locus and these two alleles separate when gametes are formed, one allele going into each gamete. This genetic concept is known as the

principle of segregation.

The figure represents a pair of homologous chromosomes. Assign the appropriate term to each component.

question 1