Lecture 01: Sex Determination (Pozor) Flashcards
3 stages of sexual differentiation
1) chromosomal (XX or XY)
2) gonadal (ovary or testis)
3) phenotypic (male or female)
each stage depends on the previous one
what does chromosomal sex drvie?
gonadal differentiation
Main precursor to gonads
genital ridge
Mesonephros develops into what structures?
small structures near but not IN the gonads
Where is genital ridge located?
next to mesonephros and mesonephric ducts
yolk sac
first fetal membrane that provides nutrition to developing embryo. Where Primordial germ cells are located before they migrate to genital ridge to become gametes
gametes
spermatozoa and oocytes
precursor to gametes
primordial germ cells (PGCs)
migration of PGCs (start & end)
start –> yolk sac
end –> genital ridge, where they colonize
What initiates testis differentiation?
Sry (sex determining region) gene on Y chromosome (TDF - Testis determining factor)
T or F: ovarian differentiation is a default process
FALSE! Needs 2 copies of key genes from 2 X chromosomes to occur
precursor to female sexual organs
Paramesonephric duct (Mullerian duct)
precursor to male sex organs
Mesonephric duct (Wolffian duct)
Influence of testicular hormones
presence or absence influences development of tubular tract
Precursor to epididymis
mesonephric duct
What hormone do leydig cells produce?
Testosterone
What hormone do sertoli cells produce?
Anti-Mullerian Hormone (AMH) (causes regression of the mullerian duct system and induction of wolffian duct system) *****
lack of AMH –>
maintenance of female tract
3 components of wolffian duct system
epididymis, deferent duct, urethra
4 components of mullerian duct system
oviducts, uterus, cervix, crania vagina
precursor to cranial vestibule
urogenital sinus
what hormones cause physical masculinization? (2)
testosterone and DHT
Absense of testosterone/DHT –>
female physical differentiation
Most common cause of chromosonal disorder of sex. differentiation
non-disjunction of sex chromosomes or chromatids **
Meiosis I =
first division of meiosis
Meiosis II =
second division of meiosis
nondisjunction in meiosis II leads to what kind of zygotes?
half normal, and half trisomic and monosomic
Turner’s Syndrome
XO (monosomy X). underdeveloped but gonadally/phenotypically FEMALE. Usually sterile
Klinefelter’s Syndrome
XXY. Gonadally and phenotypically MALE due to Sry, but abnormal and usually sterile.
Trisomy X Syndrome
XXX. Gonadally and phenotypically FEMALE, but abnormal/UNDERdeveloped.
Mosaic and cause
all cells originate from single zygote. cause usually = non-disjunction during mitosis of early embryo
Chimera
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
Tortoiseshell cats
(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.
Freemartin
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
Test for freemartin
can’t fit 10cc of fluid in vagina (freemartins have short vagina)
Sex reversal
when chromosomal sex and gonadal sex don’t agree (i.e. XY with ovaries)
Sex reversed female
Y chromosome is present but Sry is non-functional. Undifferentiated “streak” gonads. Underdeveloped female
Sex reversed male
2 causes:
1) Sry translocated to X chromosome during meiosis and causes masculinization
2) Mutation in gene downstream of Sry
Polled Intersex Syndrome (PIS)
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
see flow chart at end of Notability lecture
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