Question 1

Women born with an extra X chromosome (XXX)are healthy and phenotypically indistinguishable from normal XX women. What is a likely explanation for this finding?
 How could you test this explanation?

Accepted Answer

The answer of Women born with an extra X chromosome...

Question 2

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

Accepted Answer

A) The two genes are linked. 
B) The two genes are linked but on different chromosomes. 
C) Recombination did not occur in the cell during meiosis. 
D) The testcross was improperly performed. 
E) Both of the characters are controlled by more than one gene.

Question 3

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?

Accepted Answer

A) 2:1 male to female 
B) 1:2 male to female 
C) 1:1 male to female 
D) 4:3 male to female 
E) 3:1 male to female

Question 4

A Barr body is normally found in the nucleus of which kind of human cell?

Accepted Answer

A) Unfertilized egg cells only 
B) Sperm cells only 
C) Somatic cells of a female only 
D) Somatic cells of a male only 
E) Both male and female somatic cells

Question 5

A nonreciprocal crossover causes which of the following products?

Accepted Answer

A) Deletion only 
B) Duplication only 
C) Nondisjunction 
D) Deletion and duplication 
E) Duplication and nondisjunction

Question 6

In order for chromosomes to undergo inversion or translocation, which of the following is required?

Accepted Answer

A) Point mutation 
B) Immunological insufficiency 
C) Advanced maternal age 
D) Chromosome breakage and rejoining 
E) Meiosis

Question 7

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

Accepted Answer

A) males are hemizygous for the X chromosome. 
B) male hormones such as testosterone often alter the effects of mutations on the X chromosome. 
C) female hormones such as estrogen often compensate for the effects of mutations on the X. 
D) X chromosomes in males generally have more mutations than X chromosomes in females. 
E) mutations on the Y chromosome often worsen the effects of X-linked mutations.

Question 8

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

Accepted Answer

A) n + 1; n + 1; n - 1; n - 1 
B) n + 1; n - 1; n; n 
C) n + 1; n - 1; n - 1; n - 1 
D) n + 1; n + 1; n; n 
E) n - 1; n - 1; n; n

Question 9

A wild-type fruit fly (heterozygous for gray body color and normal wings)is mated with a black fly with vestigial wings. The offspring have the following phenotypic distribution: wild type, 778; black-vestigial, 785; black-normal, 158; gray-vestigial, 162. What is the recombination frequency between these genes for body color and wing size?

Accepted Answer

The answer of A wild-type fruit fly (heterozygous for gray...

Question 10

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

Accepted Answer

A) Deletion 
B) Disjunction 
C) Inversion 
D) Translocation 
E) Duplication

Question 11

A phenotypically normal prospective couple seeks genetic counseling because the man knows that he has a translocation of a portion of his chromosome 4 that has been exchanged with a portion of his chromosome 12. Although he is normal because his translocation is balanced, he and his wife want to know the probability that his sperm will be abnormal. What is your prognosis regarding his sperm?

Accepted Answer

A) 1/4 will be normal, 1/4 with the translocation, 1/2 with duplications and deletions. 
B) All will carry the same translocation as the father. 
C) None will carry the translocation since abnormal sperm will die. 
D) His sperm will be sterile and the couple might consider adoption. 
E) 1/2 will be normal and the rest with the father's translocation.

Question 12

Refer to Figure 15.2 to answer the following questions.
 
$\text {The numbers in the boxes are the recombination}$
 $\text {frequencies in between the genes (in percent).}$
 
Figure 15.2
-Which of the following two genes are closest on a genetic map of Drosophila?

Accepted Answer

A) b and vg 
B) vg and cn 
C) rb and cn 
D) cn and b 
E) b and rb

Question 13

A cell that has 2n + 1 chromosomes is

Accepted Answer

A) trisomic. 
B) monosomic. 
C) euploid. 
D) polyploid. 
E) triploid.

Question 14

Abnormal chromosomes are frequent in malignant tumors. Errors such as translocations may place a gene in close proximity to different control regions. Which of the following might then occur to make the cancer worse?

Accepted Answer

A) An increase in non-disjunction 
B) Expression of inappropriate gene products 
C) A decrease in mitotic frequency 
D) Death of the cancer cells in the tumor 
E) Sensitivity of the immune system

Question 15

Of the following human aneuploidies, which is the one that generally has the most severe impact on the health of the individual?

Accepted Answer

A) 47, +21 
B) 47, XXY 
C) 47, XXX 
D) 47, XYY 
E) 45, X

Question 16

Mitochondrial DNA is primarily involved in coding for proteins needed for electron transport. Therefore in which body systems would you expect most mitochondrial gene mutations to be exhibited?

Accepted Answer

A) The immune system and the blood 
B) Excretory and respiratory systems 
C) The skin and senses 
D) Nervous and muscular systems 
E) Circulation

Question 17

Women with Turner syndrome have a genotype characterized as which of the following?

Accepted Answer

A) aabb 
B) Mental retardation and short arms 
C) A karyotype of 45, X 
D) A karyotype of 47, XXX 
E) A deletion of the Y chromosome

Question 18

Refer to Figure 15.2 to answer the following questions.
 
$\text {The numbers in the boxes are the recombination}$
 $\text {frequencies in between the genes (in percent).}$
 
Figure 15.2
-In a series of mapping experiments, the recombination frequencies for four different linked genes of Drosophila were determined as shown in the figure. What is the order of these genes on a chromosome map?

Accepted Answer

A) rb-cn-vg-b 
B) vg-b-rb-cn 
C) cn-rb-b-vg 
D) b-rb-cn-vg 
E) vg-cn-b-rb

Question 19

Pseudohypertrophic muscular dystrophy is an inherited disorder that causes gradual deterioration of the muscles. It is seen almost exclusively in boys born to apparently normal parents and usually results in death in the early teens. Is this disorder caused by a dominant or a recessive allele?
 Is its inheritance sex-linked or autosomal?
 How do you know?
 Explain why this disorder is almost never seen in girls.

Accepted Answer

The answer of Pseudohypertrophic muscular dystrophy is an inherited disorder...

Question 20

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

Accepted Answer

A) All the gametes will be diploid. 
B) Half of the gametes will be n + 1, and half will be n - 1. 
C) 1/4 of the gametes will be n + 1, one will be n - 1, and two will be n. 
D) There will be three extra gametes. 
E) Two of the four gametes will be haploid, and two will be diploid.

Exam 15: The Chromosomal Basis of Inheritance

Women born with an extra X chromosome (XXX)are healthy and phenotypically indistinguishable from normal XX women. What is a likely explanation for this finding? How could you test this explanation?