Sex Determination

Question 1

Describe the chromosomes in a zygote?

Answer 1

23 chromosomes from its mother and 23 from its father
- 23 pairs of homologous chromosomes
Note:
The first 22 pairs are called autosomal chromosomes
The 23rd pair are the sex chromosomes

Question 2

Describe the sex pair in women?

Answer 2

consist of two X chromosomes

Question 3

Describe the sex pair in men?

Answer 3

consist of one X and one Y chromosome

Question 4

Why are gametes haploid?

Answer 4

they only contain half the number of chromosomes of the diploid parent

• Half of the sperm contain X and half contain Y
• All ova contain X chromosomes

Question 5

Describe how sperm can determine the gender of the zygote?

Answer 5

• If a Y-bearing sperm fertilizes the ovum the zygote will be XY and male
• If an X-bearing sperm fertilizes the ovum the zygote will be XX and female

Question 6

What is the state of the 2 X chromosomes in a woman?

Answer 6

• only one of each pair of X chromosomes remains active

- The other X chromosome forms a clump of inactive “heterochromatin” seen as a dark spot called a Barr body

Question 7

When are the gonads of males and females similar in appearance?

Answer 7

first 40 days of development

- At this stage the embryonic structures have the potential to become either testes or ovaries

Question 8

What is testis-determining factor (TDF)?

Answer 8

The substance that promotes the conversion of gonads into testes

Question 9

What is the gene for testis-determining factor and where is it located?

Answer 9

sex-determining region of the Y (SRY)

- is located on the short arm of the Y chromosome

Question 10

When do seminiferous tubules appear in embryonic development?

Answer 10

43-50 days following conception

Question 11

When do sertoli and leydig cells appear in embryonic development?

Answer 11

Sertoli cells appear at about day 42 while

Leydig cells appear at about day 65

Question 12

When do ovarian follicles appear in embryonic development?

Answer 12

second trimester of pregnancy (about 105 days)

Question 13

Function of embryonic Leydig cells in sex determination in embryonic development?

Answer 13

secrete large amounts of androgens (testosterone).
- Testosterone serves the very important function of masculinizing the embryonic structure
Note: The developing testes move within the abdominal cavity and gradually descend into the scrotum

Question 14

Male accessory glands are derived from?

Answer 14

Wolffian (mesonephric) ducts

Question 15

Female accessory organs are derived from?

Answer 15

Mullerian (paramesonephric) ducts

Question 16

Describe the development of accessory sex organs and external genitalia?

Answer 16

The Wolffian and Mullerian duct systems are present in both male and female embryos between day 25 to day 50, so the embryos of both sexes have the potential to form the accessory organs characteristic of either sex

Question 17

Testes castration from male embryonic animal results?

Answer 17

regression of the Wolffian ducts and development of the Mullerian ducts into female accessory organs
- Female accessory organs therefore develop as a result of the absence of testes rather than as a result of the presence of ovaries

Question 18

Testes castration from male embryonic animal results?

Answer 18

regression of the Wolffian ducts and development of the Mullerian ducts into female accessory organs
- Female accessory organs therefore develop as a result of the absence of testes rather than as a result of the presence of ovaries

Question 19

What do Sertoli cells in embryonic development secrete?

Answer 19

Mullerian inhibition factor (MIF)

- a peptide that causes regression of the Mullerian ducts beginning at about day 60

Question 20

Describe how the secretion of testosterone by Leydig cells aids in the development of accessory sex organs and external genitalia?

Answer 20

causes growth and development of the Wolffian ducts into male accessory sex organs