Mastering Biology: Chapter 15

1/16

A man with hemophilia has a daughter of normal phenotype. She marries a man who is normal for the trait. If the couple has four sons, what is the probability that all four will be born with hemophilia?

0

A man with hemophilia has a daughter of normal phenotype. She marries a man who is normal for the trait. What is the probability that a daughter of this mating will be hemphiliac?

1/2

A man with hemophilia has a daughter of normal phenotype. She marries a man who is normal for the trait. What is the probability that a son will be hemophiliac?

1/2

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

HT

A sexually reproducing animal has two unlinked genes, one for head shape (H) and one for tail length (T). Its genotype is HhTt. What is a possible gamete from this organism?

None of the females will have white yes. (All of the females will have red eyes because they will inherit the dominant red-eye allele from their male parent.)

A white-eyed female Drosophila is crossed with a red-eyed male Drosophila. Which statement below correctly described the results?

activation of the XIST gene on the X chromosome that will become the Barr body.

All female mammals have one active X chromosome per cell instead of two. What causes this to happen?

One-half of the daughters of an affected father and a carrier mother could have this condition.

Duchenne muscular dystrophy is a series condition caused by a recessive allele of a gene on the human X chromosome. The patients have muscles that weaken over time because they have absent or decreased dystrophin, a muscle protein. They rarely live past their 20s. How likely is it for a woman to have this condition?

A male inherits only one allele of the X-linked gene controlling hair color.

Generally, only female cats have the tortoiseshell phenotype for fur color. Which of the following statements explains this phenomenon?

2:1 male to female

In birds, sex is determined by a ZW chromosome scheme. Males are ZZ and females are ZW. A recessive lethal allele that causes death of the embryo is sometimes present on the Z chromosome in pigeons. What would be the sex ratio in the offspring of a cross between a male that is heterozygous for the lethal allele and a normal female?

tortoiseshell females; black males

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?

The male gamete determines sex because each male gamete can contribute either an X or a Y chromosome

In humans, what determines the sex of offspring and why?

recessive, sex-linked

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. Due to the severity of the disease, the boys die in their teens. Is this disorder likely to be caused by a dominant or recessive allele? Is the inheritance of this trait sex-linked or autosomal?

X^N X^n and X^N Y

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?

The two genes are likely to be located on different chromosomes.

What does a recombination frequency of 50% indicate?

wild type

What name is given to the most common phenotype in a natural population?

The two genes are closely linked on the same chromosome.

What would explain a testcross involving F1 dihybrid flies in which more parental-type offspring than recombinant-type offspring are produced?

The gene involved is located on the X chromosome.

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 is present in both males and females. (All cells have at least one functional X chromosome.)

Which of the following is true of an X-linked gene, but not of a Y-linked gene?

Crossovers between these genes result in chromosomal exchange.

Which of the following occurrence describes how recombination between linked genes comes about?

100%

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

Males are hemizygous for the X chromosome

Why are males more often affected y sex-linked traits that females?