Lecture 01: Sex Determination (Pozor)

Question 1

3 stages of sexual differentiation

Answer 1

1) chromosomal (XX or XY)
2) gonadal (ovary or testis)
3) phenotypic (male or female)

each stage depends on the previous one

Question 2

what does chromosomal sex drvie?

Answer 2

gonadal differentiation

Question 3

Main precursor to gonads

Answer 3

genital ridge

Question 4

Mesonephros develops into what structures?

Answer 4

small structures near but not IN the gonads

Question 5

Where is genital ridge located?

Answer 5

next to mesonephros and mesonephric ducts

Question 6

yolk sac

Answer 6

first fetal membrane that provides nutrition to developing embryo. Where Primordial germ cells are located before they migrate to genital ridge to become gametes

Question 7

gametes

Answer 7

spermatozoa and oocytes

Question 8

precursor to gametes

Answer 8

primordial germ cells (PGCs)

Question 9

migration of PGCs (start & end)

Answer 9

start –> yolk sac

end –> genital ridge, where they colonize

Question 10

What initiates testis differentiation?

Answer 10

Sry (sex determining region) gene on Y chromosome (TDF - Testis determining factor)

Question 11

T or F: ovarian differentiation is a default process

Answer 11

FALSE! Needs 2 copies of key genes from 2 X chromosomes to occur

Question 12

precursor to female sexual organs

Answer 12

Paramesonephric duct (Mullerian duct)

Question 13

precursor to male sex organs

Answer 13

Mesonephric duct (Wolffian duct)

Question 14

Influence of testicular hormones

Answer 14

presence or absence influences development of tubular tract

Question 15

Precursor to epididymis

Answer 15

mesonephric duct

Question 16

What hormone do leydig cells produce?

Answer 16

Testosterone

Question 17

What hormone do sertoli cells produce?

Answer 17

Anti-Mullerian Hormone (AMH) (causes regression of the mullerian duct system and induction of wolffian duct system) *****

Question 18

lack of AMH –>

Answer 18

maintenance of female tract

Question 19

3 components of wolffian duct system

Answer 19

epididymis, deferent duct, urethra

Question 20

4 components of mullerian duct system

Answer 20

oviducts, uterus, cervix, crania vagina

Question 21

precursor to cranial vestibule

Answer 21

urogenital sinus

Question 22

what hormones cause physical masculinization? (2)

Answer 22

testosterone and DHT

Question 23

Absense of testosterone/DHT –>

Answer 23

female physical differentiation

Question 24

Most common cause of chromosonal disorder of sex. differentiation

Answer 24

non-disjunction of sex chromosomes or chromatids **

Question 25

Meiosis I =

Answer 25

first division of meiosis

Question 26

Meiosis II =

Answer 26

second division of meiosis

Question 27

nondisjunction in meiosis II leads to what kind of zygotes?

Answer 27

half normal, and half trisomic and monosomic

Question 28

Turner’s Syndrome

Answer 28

XO (monosomy X). underdeveloped but gonadally/phenotypically FEMALE. Usually sterile

Question 29

Klinefelter’s Syndrome

Answer 29

XXY. Gonadally and phenotypically MALE due to Sry, but abnormal and usually sterile.

Question 30

Trisomy X Syndrome

Answer 30

XXX. Gonadally and phenotypically FEMALE, but abnormal/UNDERdeveloped.

Question 31

Mosaic and cause

Answer 31

all cells originate from single zygote. cause usually = non-disjunction during mitosis of early embryo

Question 32

Chimera

Answer 32

cells originate from more than one zygote. Can be naturally or experimentally occuring. During development, placentas from twin pregnancies fuse and blood from the two fetuses mixes before gonadal differentiation leading to hormonal mixture and masculinization of female fetus

Question 33

Tortoiseshell cats

Answer 33

(Fur color carried on X chromosome) Tortoiseshell cats are heterozygous for orange fur, but random X-inactivation results in females that are mosaics and have orange and black fur.

Question 34

Freemartin

Answer 34

An example of chimera. Calf contains a portion of cells originating from its twin due to mixed vascular beds in utero. Results in masculinization and sterility of female twin

Question 35

Test for freemartin

Answer 35

can’t fit 10cc of fluid in vagina (freemartins have short vagina)

Question 36

Sex reversal

Answer 36

when chromosomal sex and gonadal sex don’t agree (i.e. XY with ovaries)

Question 37

Sex reversed female

Answer 37

Y chromosome is present but Sry is non-functional. Undifferentiated “streak” gonads. Underdeveloped female

Question 38

Sex reversed male

Answer 38

2 causes:

1) Sry translocated to X chromosome during meiosis and causes masculinization
2) Mutation in gene downstream of Sry

Question 39

Polled Intersex Syndrome (PIS)

Answer 39

heritable condition in goats in which homozygous dominant for polled also results in expression of recessive intersex gene, which inactivates important genes for gonadal development. Results in sterility and male differentiation in females, and sperm granulomas in males. Tx = keep horned buck

Question 40

see flow chart at end of Notability lecture

Answer 40

:)