Sex differentiation & determinition

Question 1

Which layer of the primary embryonic germ layers develop into the reproductive system?

Answer 1

Mesoderm

Question 2

Define sex determination

Answer 2

Developmental decision that directs the ‘bipotential’ gonad to develop as either testis or ovary. Can be genetically controlled (mammals) or environmental (some reptiles)

Question 3

Describe the sex chromosomes of birds

Answer 3

-Called Z and W
-ZZ= male
-ZW= female
(in birds the female is heterozygous NOT the male)

Question 4

In males what causes the appearance of external penis and scrotum?

Answer 4

Dihydrotestosterone

Question 5

Describe sexual differentiation of the brain

Answer 5

MALE:
- Testosterone is secreted into blood, it then crosses BBB where it is converted to oestradiol and dihydrotestosterone. Oestradiol masculinses the brain!
FEMALE:
- Alpha fetoprotein binds to oestradiol- this means the complex cannot cross BBB. This prevents the masculinising effects of oestrodiol on the brain.

Question 6

Describe the normal morphological sexual development

Answer 6

• Pregonadal phase: Germ cells start to migrate from yolk sac
• Bipotential gonad: Development of gonadal precursor tissue near kidneys (genital ridge)/ germ cells migrate to genital ridge
• Primary sexual differentiation: differentiation of reproductive tissues/ reflects nature of the gonads
• Secondary sexual differentiation: development of secondary sexual characteristics/ marks sexes as phenotypically distinct

Question 7

What does SRY protein do?

Answer 7

Stimulates the testes to develop–> the sertoli cells then secrete AMH

Question 8

In males what becomes the efferent ducts?

Answer 8

Mesonephric tubules

Question 9

In males what does the mesonephric ducts develop into?

Answer 9

Epididymus and ductus deferens

Question 10

Describe the difference in males and females regarding the migration and proliferation of germ cells

Answer 10

XY= arrested at G0 stage when they enter the urogenital ridge, 
XX= begin meiosis and are then arrested at prophase 1 until sexual maturation

Question 11

When does testes descent normally occur and which species are the exception?

Answer 11

Normally between middle/ end of fetal development
Horses= late preg or a few days after birth
Dogs= up to 8 days after birth
Elephants/ whales= stay in original position

Question 12

In what situation can a free martin occur?

Answer 12

When a heifer calf is born twin to a bull calf - it is caused by the anastomosing of the two calves blood supplies leading to the heifer being exposed to AMH and testosterone.

Question 13

What is cryptorchidism?

Answer 13

Failure of testes to descend into scrotum

Question 14

What is an inguinal herniation?

Answer 14

Portion of intestine passes through inguinal canal into vaginal cavity

Question 15

What is hypospadias?

Answer 15

Urethral opening at base of penis