Chapter 15 - The Chromosomal Basis of Inheritance

Question 1

Which of the following is/are part of the chromosomal theory of inheritance?

a. Genes are located on chromosomes.
b. Homologous chromosomes and their associated genes undergo segregation during meiosis.
c. Chromosomes and thier associated genes undergo independent assortment in gamete formation.
d. Mendel’s laws of inheritance relate to the behavior of chromosomes in meiosis.
e. All of the above are included.

Answer 1

e. All of the above are included.

Question 2

A wild type is

a. the phenotype found most commonly in nature.
b. the dominant allele.
c. designated by a small letter if it is recessive or a capital letter if it is dominant.
d. a trait found on the X chromosome.
e. your basic party animal.

Answer 2

a. the phenotype found most commonly in nature.

Question 3

Sex-linked traits

a. are carried on an autosome but expressed only in males.
b. are coded for by genes located on a sex chromosome.
c. are found in only one or the other sex, depending on the sex-determination system of the species.
d. are always inherited from the mother in mammals and fruit flies.
e. depend on whether the gene was inherited from the mother or the father.

Answer 3

b. are coded for by genes located on a sex chromosome.

Question 4

Linkage and cytogenetic maps for the same chromosome

a. are both based on mutant phenotypes and recombination data.
b. may have diffferent orders of genes.
c. have both the same order of genes and intergenic distances.
d. have the same order of genes but different intergenic distances.
e. are created using chromosomal abnormalities.

Answer 4

d. have the same order of genes but different intergenic distances.

Question 5

The genetic event that results in Turner syndrome (X0) is probably

a. nondisjunction.
b. deletion.
c. parental imprinting.
d. monoploidy.
e. independent assortment.

Answer 5

a. nondisjunction.

Question 6

A 1:1:1:1 ratio of offspring from a dihybrid test-cross indicates that

a. the genes are linked.
b. the dominant organism was homozygous.
c. crossing over has occurred.
d. the genes are 25 map units apart.
e. the genes are not linked or are more than 50 map units apart.

Answer 6

e. the genes are not linked or are more than 50 map units apart.

Question 7

Genes A and B are linked and 12 map units apart. A heterozygous individual, whose parents were AAbb and aaBB, would be expected to produce gametes in the following frequencies:

a. 44% AB 6% Ab 6% aB 44% ab
b. 6% AB 44% Ab 44% aB 6% ab
c. 12% AB 38% Ab 38% aB 12% ab
d. 6% AB 6% Ab 44% aB 44% ab
e. 38% AB 12% Ab 12% aB 38% ab

Answer 7

b. 6% AB 44% Ab 44% aB 6% ab

Question 8

A female tortoiseshell cat is heterozygous for the gene that determines black or orange coat color, which is located on the X chromosome. A male tortoiseshell cat

a. could not occur
b. is hemizygous at this locus.
c. must have resulted from a nondisjunction and has a Barr body in each of his cells.
d. must have two alleles for coat color in each of his cells, one from his father and one from his mother.
e. would be hermaphroditic.

Answer 8

c. must have resulted from a nondisjunction and has a Barr body in each of his cells.

Question 9

What do we mean when we say that a few of the genes for Mendel’s pea characters were physically linked but genetically unlinked?

a. The genes are on the same chromosome, but they are more than 50 map units apart.
b. The genes assort independently even though the chromosomes they are on travel to the metaphase plate together.
c. Their alleles segregate in anaphase I, and each gamete receives a single allele for all of these genes.
d. Dihybrid crosses with these genes produce more than 50% recombinant offspring even though they are on the same chromosome.
e. Mendel could not determine that the genes were on the same chromosome because he did not perform dihybrid crosses with these particular gene pairs.

Answer 9

a. The genes are on the same chromosome, but they are more than 50 map units apart.

Question 10

Genomic imprinting

a. explains cases in which the phenotypic effect of an allele depends on the gender of the parent from whom that allele is inherited.
b. may involve the silencing of an allele by methylation so that offspring inherit ony one active copy of a gene.
c. occurs more often in females because of the larger maternal contribution of cytoplasm.
d. is more likely to occur in offspring of older mothers.
e. involves both a and b.

Answer 10

e. involves both a and b.

Question 11

A cross of a wild-type red-eyed female Drosophila with a violet-eyed male produces all red-eyed offspring. If the gene is sex-linked, what should the reciprocal cross (violet-eyed female x red-eyed male) produce? (Assume that the red allele is dominant to the violet allele.)

a. all violet-eyed flies.
b. 3 red-eyed flies to 1 violet-eyed fly
c. a 1:1 ratio of red and violet eyes in both males and females
d. red-eyed females and violet-eyed males
e. all red-eyed flies

Answer 11

d. red-eyed females and violet-eyed males

Question 12

Which of the following chromosomal alterations does not alter genic balance but may alter phenotype because of differences in gene expression?

a. deletion
b. inversion
c. duplication
d. nonidentical duplication
e. nondisjunction

Answer 12

b. inversion

Question 13

Two true-breeding Drosophila are crossed: a normal-winged, red-eyed female and a miniature-winged, vermilion-eyed male. The F₁ all have normal wings and red eyes. F₁ offspring are crossed with miniature-winged, vermilion-eyed flies. The following offspring of that cross were “scored”:

233 normal wing, red eye

247 miniature wing, vermilion eye

7 normal wing, vermilion eye

13 miniature wing, red eye

From these results, you could conclude that the alleles for miniature wings and vermilion eyes are

a. both X-linked and dominant.
b. located on autosomes and dominant.
c. recessive, and these genes are located 4 map units apart.
d. recessive, and these genes are located 20 map units apart.
e. recessive, and the deviation from the expected 9:3:3:1 ratio is due to epistasis.

Answer 13

c. recessive, and these genes are located 4 map units apart.

Question 14

Tests of social behavior given to Turner syndrome volunteers (who are X0) found a correlation between scores on “behavioral inhibition” tasks and the source of the lone X chromosome. These test results appear to be an example of

a. parental imprinting of a gene on the X chromosome.
b. Y-linked inheritance.
c. meiotic nondisjunction.
d. chromosomal reciprocal translocation.
e. nonreciprocal crossover.

Answer 14

a. parental imprinting of a gene on the X chromosome.

Question 15

Suppose that alleles for a sex-linked character for wing shape in flies show incomplete dominance. The X⁺ allele codes for pointed wings, the X^r for round wings, and X⁺X^r individuals have oval wings. In a cross between an oval-winged female and a round-winged male, the following offspring were observed: oval-winged females, round-winged females, pointed-wing males, and round-winged males. A rare pointed-winged female was noted. Cytological study revealed that she had 2 X chromosomes. What could account for the unusual offspring?

a. a crossover between the two X chromosomes
b. a crossover between the X and Y chromosomes
c. a nondisjunction in meiosis II between two X⁺ chromatids
d. a nondisjunction between the X and Y chromosomes, producing some sperm with no sex chromosome
e. Both c and d together could produce an X⁺X⁺ female when an XX ovum was fertilized by a sperm in which there was no sex chromosome.

Answer 15

e. Both c and d together could produce an X⁺X⁺ female when an XX ovum was fertilized by a sperm in which there was no sex chromosome.

Question 16

Some girls who fail to undergo puberty are found to have Swyer syndrome, a condition in which they are externally female but have an XY genotype. Which of the following may explain the origin of this syndrome?

a. A mutation in the XIST gene, which codes for RNA molecules that coat the X chromosome and initiate X-inactivation, must have occurred.
b. A nondisjunction in the ovum from th mother resulted in both sex chromosomes coming from the father. Genomic imprinting of the father’s X chromosome then caused the development of a female phenotype.
c. These individuals are actually XXY; the second X is not seen because it is condensed into a Barr body. They have small testes and are sterile, but otherwide appear female.
d. A mutation of deletion of the SRY gene on the Y chromosome prevented development of testes and production of male sex hormones required for a male phenotype.
e. A translocation of part of an X chromosome to the Y chromosome resulted in a double dose of female-determining genes.

Answer 16

d. A mutation of deletion of the SRY gene on the Y chromosome prevented development of testes and production of male sex hormones required for a male phenotype.

Question 17

A mutation in a mitochondrial gene has been linked to a rare muscle-wasting disease in humans. This disease is

a. found more often in males than females.
b. found more often in females than males.
c. inherited in a simple Mendelian fashion.
d. caused by a translocation of a nuclear gene to the mitochondria.
e. inherited from the mother and equally as likely to occur in male as female offspring.

Answer 17

e. inherited from the mother and equally as likely to occur in male as female offspring.

Question 18

In which of the following would you expect to find a Barr body?

a. an ovum
b. a sperm
c. a liver cell of a man
d. a liver cell of a woman
e. a mitochondrion

Answer 18

d. a liver cell of a woman

Question 19

A cross between a wild-type mouse and a dwarf mouse homozygous for a recessive mutation in the Igf2 gene produces heterozygous offspring that are normal if the dwarf parent was the mother, but dwarf if the dwarf parent was the father. Which of the following explains these results?

a. sex-linked inheritance
b. monosomy
c. genomic imprinting
d. inheritance of mitochondrial genes
e. a mutant XIST allele

Answer 19

c. genomic imprinting

Question 20

Which of the following statements is not true about genetic recombination?

a. Recombination of linked genes occurs by crossing over.
b. Recombination of unlinked genes occurs by independent assortment of chromosomes.
c. Genetic recombination results in offspring with combinations of traits that differ from the phenotypes of both parents.
d. Recombination offspring outnumber parental-type offspring when two genes are 50 map units apart on a chromosome.
e. The number of recombinant offspring is proportional to the distance between two gene loci on a chromosome.

Answer 20

d. Recombination offspring outnumber parental-type offspring when two genes are 50 map units apart on a chromosome.