Chapter 1

Question 1

Which of the following is a major character- istic of meiosis I?
(A) Splitting of the centromere
(B) Pairing of homologous chromosomes
(C) Reducing the amount of DNA to 1N
(D) Achieving the diploid number of chromo-
somes
(E) Producing primordial germ cells

Answer 1

B. Pairing of homologous chromosomes (synapsis) is a unique event that occurs only during
meiosis I in the production of gametes. Synapsis is necessary so that crossing over can occur.

Question 2

In the process of meiosis, DNA replication of each chromosome occurs thereby forming a structure consisting of two sister chromatids attached to a single centromere. What is this structure?
(A) A duplicated chromosome
(B) Two chromosomes
(C) A synapsed chromosome
(D) A crossover chromosome
(E) A homologous pair

Answer 2

A. The structure formed is a duplicated chromosome. DNA replication occurs so that the amount of DNA is doubled (2 x 2N = 4N). However, the chromatids remain attached to the cen- tromere forming a duplicated chromosome.

Question 3

All primary oocytes are formed by 
(A) week 4 of embryonic life
(B) month 5 of fetal life
(C) birth
(D) month 5 of infancy (E) puberty

Answer 3

B. During early fetal life, oogonia undergo mitotic divisions to populate the developing ovary. All the oogonia subsequently give rise to primary oocytes by month 5 of fetal life; at birth no oogonia are present in the ovary. At birth, a female has her entire supply of primary oocytes to carry her through reproductive life.

Question 4

In the production of female gametes, which of the following cells can remain dormant for 12 to 40 years?
(A) Primordial germ cell 
(B) Primary oocyte
(C) Secondary oocyte 
(D) First polar body
(E) Second polar body

Answer 4

B. Primary oocytes are formed by month 5 of fetal life and remain dormant until puberty, when hormonal changes in the young woman stimulate the ovarian and menstrual cycles. From 5 to 15, oocytes then begin maturation with each ovarian cycle throughout the woman’s repro- ductive life.

Question 5

Approximately how many sperm are ejac-
ulated by a normal fertile male during sexual
intercourse? 
(A) 10 million
(B) 20 million
(C) 35 million 
(D) 100 million
(E) 350 million

Answer 5

E. A normal fertile male ejaculates about 3.5 mL of semen containing about 100 million sperm/mL (3.5 mL x 100 million = 350 million).

Question 6

A young woman enters puberty with approximately 40,000 primary oocytes in her ovary. About how many of these primary oocytes will be ovulated over the entire repro- ductive life of the woman?
(A) 40,000
(B) 35,000
(C) 480
(D) 48
(E) 12

Answer 6

C. Over her reproductive life, a woman ovulates approximately 480 oocytes. A woman ovu- lates 12 primary oocytes per year provided that she is not using oral contraceptives, does not become pregnant, or does not have any anovulatory cycles. Assuming a 40-year reproductive period, 40 x 12 = 480.

Question 7

How much DNA does a primary spermato- cyte contain?
(A) 1N 
(B) 2N 
(C) 4N 
(D) 6N 
(E) 8N

Answer 7

C. Type B spermatogonia give rise to primary spermatocytes by undergoing DNA replication, thereby doubling the amount of DNA (2 x 2N = 4N) within the cell.