# CHAPTER 13

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### 1/4

A man and woman are both of normal pigmentation, but both have one parent who is albino (without melanin pigmentation). Albinism is an autosomal (not sex-linked) recessive trait. What is the probability that their first child will be an albino?

### (a) Gg × Gg; (b) genotypic = 1:2:1, phenotypic = 3:1

Gray seed color in peas is dominant to white. Assume that Mendel conducted a series of experiments where plants with gray seeds were crossed among themselves, and the following progeny were produced: 302 gray and 98 white. (a) What is the most probable genotype of each parent? (b) Based on your answer in (a) above, what genotypic and phenotypic ratios are expected in these progeny? (Assume the following symbols: G = gray and g = white.)

### 3/8

Phenylketonuria is an inherited disease caused by a recessive autosomal allele. If a woman and her husband are both carriers, what is the probability that their first child will be a phenotypically normal girl?

### 1/8

Assuming independent assortment for all gene pairs, what is the probability that the following parents, AABbCc × AaBbCc, will produce an AaBbCc offspring?

### 1/64

Suppose two AaBbCc individuals are mated. Assuming that the genes are not linked, what fraction of the offspring are expected to be homozygous recessive for the three traits?

### 1:1

When Mendel crossed yellow-seeded and green-seeded pea plants, all the offspring were yellow seeded. When he took these F1 yellow-seeded plants and crossed them to green-seeded plants, what genotypic ratio is expected?

### phenotypes - wild, vestigial, hairy, vestigial hairy; numbers expected - wild (576), vestigial (192), hairy (192), vestigial hairy (64)

In Drosophila melanogaster, vestigial (short) wings (vg) are caused by a recessive allele of a gene that independently assorts with a gene pair that influences body hair. Hairy (h) results in a hairy body. A cross is made between a fly with normal wings and a hairy body and a fly with vestigial wings and a normal body. The phenotypically normal F1 flies were crossed among each other, and 1024 F2 flies were reared. What phenotypes would you expect in the F2, and in what actual numbers (not ratios) would you expect to find them?

### The black and vestigial loci are linked.

A heterozygous, but phenotypically wild-type fruit fly (gray body color and normal wings) was mated to a black fly with vestigial wings. The offspring had the following phenotypic distribution: wild type, 720; black-vestigial, 780; black-normal, 280; gray-vestigial, 220. What conclusion is likely from these results?

### 2:1 male to female

In birds, sex is determined by a ZW chromosome scheme that is much like the typical XY scheme seen in humans and many other organisms, except that the system is reversed: Males are ZZ (similar to XX in humans) and females are ZW (similar to XY in humans). A lethal recessive allele that causes death of the embryo occurs on the Z chromosome in pigeons. What would be the sex ratio in the offspring of a cross between a male heterozygous for the lethal allele and a normal female?

### 1/4

Hemophilia is caused by several genetic factors; one, a recessive allele of an X-linked gene, is the subject of this problem. Assume that a man with hemophilia marries a normal woman whose father had hemophilia. What is the probability that they will have a daughter with hemophilia?

### ½

Hemophilia is caused by several genetic factors; one, a recessive allele of an X-linked gene, is the subject of this problem. Assume that a man with hemophilia marries a normal woman whose father had hemophilia. What is the probability that their first son will have hemophilia?

### all of his daughters

A man who carries an allele of an X-linked gene will pass it on to ________.

### (a) 1/2; (b) no

Glucose-6-phosphate dehydrogenase deficiency (G6PD) is inherited as a recessive allele of an X-linked gene in humans. A woman whose father suffered from G6PD marries a normal man. (a) What proportion of their sons is expected to be G6PD? (b) If the husband was not normal but was G6PD deficient, would you change your answer in part (a)?

In a Drosophila experiment, a cross was made between homozygous wild-type females and yellow-bodied males. All of the resulting F1s were phenotypically wild type. However, adult flies of the F2 generation (resulting from matings of the F1s) had the characteristics shown in the figure above: (a) Is the mutant allele for yellow body recessive or dominant? (b) Is the yellow locus autosomal (not X-linked) or X-linked?

### 15

A homozygous tomato plant with red fruit and yellow flowers was crossed with a homozygous tomato plant with golden fruit and white flowers. The F1 all had red fruit and yellow flowers. The following phenotypes were obtained in the F2: Red fruit and yellow flowers - 41 Red fruit and white flowers - 7 Golden fruit and yellow flowers - 8 Golden fruit and white flowers - 44 How many map units separate these genes?

### One-half of their daughters will have normal color vision and brown eyes; 1/2 of their daughters will have normal color vision and blue eyes.

In humans, blue eyes are inherited as a recessive autosomal trait and color blindness is an X-linked recessive trait. A woman with blue eyes and normal color vision whose father was color blind marries a man who also has normal color vision. He has brown eyes but his mother had blue eyes. Which of the following do you expect to be true for their daughters?

### 100%

Regarding an allelic pair for flower color in snapdragons, heterozygotes have pink flowers, whereas the two homozygotes have red flowers or white flowers. When plants with red flowers are crossed with plants with white flowers, what proportion of the offspring is expected to have pink flowers?

### incomplete dominance

Snapdragons are flowers that come in a variety of colors, including red, pink, and white. A series of crosses with snapdragons having flowers of different colors produced the following results: pink × pink: 27 pink, 13 red, 14 white red × red: all red white × white: all white pink × white: 29 pink, 26 white pink × red: 28 pink, 27 red white × red: all pink Based on the results, what is the most reasonable explanation for the inheritance of these flower colors?

### 15

Whenever the dominant allele of either (or both) gene A or gene B is present, red color is produced. A cross of AaBb × AaBb can be expected to yield how many red offspring out of 16? Assume the genes are not linked.

### A and B

In humans, ABO blood types refer to glyocproteins in the membranes of red blood cells. There are three alleles for this autosomal gene: IA, IB, and i. The IA allele codes for the A glycoprotein, The IB allele codes for the B glycoprotein, and the i allele doesn't code for any membrane glycoprotein. IA and IB are codominant, and i is recessive to both IA and IB. People with A type blood have the genotypes IAIA or IAi, people with type B blood are IBIB or IBi, people with type AB blood are IAIB, and people with O type blood are ii. If a woman with type AB blood marries a man with type O blood, which of the following blood types could their children possibly have?

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