The Chromosomal Basis of Inheritance

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?

A. The involved gene was on the X chromosome.

B. The involved gene was on the Y chromosome.

C. Other female-specific factors influence eye color in flies.

D. The involved gene was on an autosome.

E. Other male-specific factors influence eye color in flies.

What does a frequency of recombination of 50% indicate?

A. The genes are located on sex chromosomes.

B. Independent assortment is hindered.

C. Abnormal meiosis has occurred.

D. All of the offspring have combinations of traits that match one of the two parents.

E. The two genes likely are located on different chromosomes or far apart on the same chromosome.

Most calico cats are female because

A. The males die during embryonic development.

B. Multiple crossovers on the Y chromosome prevent orange pigment production.

C. the Y chromosome has a gene blocking orange coloration.

D. Only females have Barr bodies.

E. A male inherits only one of the two X-linked genes controlling hair color.

If a pair of homologous chromosomes fails to separate during anaphase of meiosis I, what will the chromosome number of the four resulting gametes with respect to the normal haploid number (n)?

Hypophosphatemia (vitamin D-resistant rickets) is inherited as a X-linked dominant disorder. An unaffected woman mates with a male with hypophosphatemia. What is the expected phenotypic ratio of their offspring?

A. 1 daughter with hypophosphatemia: 1 normal son

B. 3 normal daughters: 1 son with hypophosphatemia

C. 2 normal daughters: 1 normal son: 1 son with hypophosphatemia

D. 1 normal daughter: 1 daughter with hypophosphatemia

E. 1 normal daughter: 1 son with hypophosphatemia

A man who carries an X-linked allele will pass it on to

Males are more often affected by sex-linked traits that females because

A. X chromosomes in males generally have more mutations that X chromosomes in females.

B. Female hormones such as estrogen often compensate for the effects of mutations on the X.

C. Male hormones such as testosterone often exacerbate the effects of mutations on the X chromosome.

D. Mutations on the Y chromosome often exacerbate the effects of X-linked mutations.

E. Males are hemizygous for the X chromosome.

Which of the following statements is true regarding genomic imprinting?

A. It is greatest in females because of the larger maternal contribution of cytoplasm.

B. All the choices are correct.

C. It may explain the transmission of Duchenne muscular dystrophy.

D. It explains cases in which the gender of the parent from whom an allele is inherited affects the expression of that allele.

E. It involves an irreversible alteration in the DNA sequence of imprinted genes.

A map of a chromosome that includes the positions of genes relative to visible chromosomal features, such as stained bands, is called a

The recombination frequency between gene A and gene B is 8.4%, the recombination frequency between gene A and gene C is 6.8%, and the recombination frequency between gene B and gene C is 15.2%. Which is the correct arrangement of these genes?

What is the mechanism for the production of genetic recombinants?

A. nondisjunction

B. X inactivation

C. Deletions and duplications during meiosis

D. Methylation of cytosine

E. Crossing over and independent assortment

If a human interphase nucleus of a person contain 3 Barr bodies, it can be assumed that the person

Which of the following is true regarding linkage maps?

A. Are a genetic map based on recombination frequencies.

B. Require preparation of karyotypes.

C. Can be used to pinpoint the precise physical position of a gene on a chromosome.

D. Reflect the frequency of crossing over between X and Y chromosomes.

E. Always have a total of 100 map units.

What do all human males inherit from their mother?

The frequency of crossing over between any two linked genes is

A. Proportional to the distance between them.

B. Determined by their relative dominance.

C. Higher if they are recessive.

D. Different between males and females.

E. The same as if they were not linked.

One possible result of chromosomal breakage is for a fragment to join a nonhomologous chromosome. This is called a (an)

SRY is

A. An autosomal gene that is required for the expression of genes on the Y chromosome.

B. A gene present on the Y chromosome that triggers male development.

C. Required for development, and males or females lacking the gene do not survive past early childhood.

D. A gene present on the X chromosome that triggers female development.

E. An autosomal gene that is required for the expression of genes on the X chromosome.

If nondisjunction occurs in meiosis II during gametogenesis, what will be the result at the completion of meiosis?

A. All the gametes will be diploid.

B. Two gametes will be n + 1, and two will be n - 1.

C. Two of the four gametes will be haploid, and two will be diploid.

D. One gamete will be n + 1, one will be n - 1, and two will be n.

E. There will be three extra gametes.

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 a son of this couple will be color-blind?

A human individual is phenotypically female, but her interphase somatic nuclei do not show the presence of Barr bodies. Which of the following statements concerning her is probably true?

A. She has two Y chromosomes.

B. She has Turner syndrome.

C. She has the normal number of sex chromosomes.

D. She has Klinefelter syndrome

E. She has an extra X chromosome.

The Chromosomal Basis of Inheritance

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