Chapter 15 Quiz Answers

In pea plants, the tall phenotype is dominant to the dwarf phenotype. If a heterozygous pea plant is crossed with a homozygous tall plant, what is the probability that the offspring will be dwarf in size?

0

A recessive allele on the X chromosome is responsible for red-green color blindness in humans. A woman with normal vision whose father is color blind marries a color-blind male. What is the probability that this couple's first son will be color blind?

1/2

Cinnabar eye color is a sex-linked, recessive characteristic in fruit flies. If a female having cinnabar eyes is crossed with a wild-type male, what percentage of the F1 males will have cinnabar eyes?

100%

A W E G |_______|_____|_____________| Between which two genes would you expect the highest frequency of recombination?

A and G

Albinism is a recessive trait. A man and woman who both have normal pigmentation have one child out of three who has albinism. What are the genotypes of this child's parents?

Both parents must be heterozygous

Why are males more often affected by sex-linked traits than females?

Males are hemizygous for the X chromosome.

If cell X enters meiosis, and nondisjunction of one chromosome occures in one of its daughter cells during meiosis II, how will this affect the gametes at the completion of meiosis?

One-quarter of the gametes descended from cell X will be n+1, one-quarter will be n-1, and half will be n

Which of the following statements regarding gene linkage is correct?

The closer two genes are on a chromosome, the lower the probability that a crossover will occur between them

A gene determines whether or not a person can taste the chemical PTC. PTC tastes bitter to people with the dominant tasting (T) allele, whereas people homozygous for the recessive "t" allele cannot taste the PTC chemical. In a class of 100 students, 64 students can taste PTC and 36 students cannot taste PTC. Which of the following statements is true?

The frequency of the non-tasting allele is 60% (i.e. 0.6)

When Thomas Hunt Morgan crossed his red-eyed F1 generation flies to each other, the F2 generation included both red- and white-eyed flies. Remarkably, all the white-eyed flies were male. What was the explanation for this result?

The gene involved is located on the X chromosome

Which of the following statements would explain a testcross involving F1 dihybrid flies in which more parental-type offspring than recombinant-type offspring are produced?

The two genes are closely linked on the same chromosome

What does a recombination frequency of 50% indicate?

The two genes are likely to be located on different chromosomes

Which of the following characteristics do homologous chromosomes exhibit?

They carry information for the same kinds of traits

Red-green color blindness is a sex-linked recessive trait in humans. Two people with normal color vision have a color-blind son. What are the genotypes of the parents?

X^N X^n and X^N Y

Down Syndrome occurs if an individual has three of chromosome "23", rather than the normal homologous pair. The cause of this situation is the nondisjuntion of a pair of homologous chromosomes, or a pair of sister chromatids, during meiosis. What do we call this category of chromosome disorder?

aneuploidy9

A man who is a dwarf with achondroplasia and normal vision marries a color-blind woman of normal height. The man's father was six feet tall, and both the woman's parents were of average height. Dwarfism caused by achondroplasia is autosomal dominant, and red-green color blindness is X-linked recessive. How many of their daughters might be expected to be color-blind with achondroplasia?

none

Pseudohypertrophic muscular dystrophy is a human disorder that causes gradual deterioration of the muscles. Only boys are affected, and they are always born to phenotypically normal parents. Is this disorder likely to be caused by a dominant or recessive allele? Is the inheritance of this trait sex-linked or autosomal?

recessive, sex-linked

In cats, black fur color is determined by an X-linked allele, the other allele at this locus determines orange color. The heterozygote is tortoiseshell. What kinds of offspring would you expect from the cross of a black female and an orange male?

tortoiseshell females; black males

One possible result of chromosomal breakage is for a fragment to join a nonhomologous chomosome. What is this type of chromosomal alteration called?

translocation