Sex Determination Flashcards
3 stages of sexual differentiation
chromosome (XX, XY)
Gonadal (testes or ovaries)
Phenotypic (male or female characteristics)
each stage depends on previous
Male differentiation
Sex determining region (SRY protein/ TDF)
testes develop
sertoli cells secrete anti mullerian hormone (AMH)
Male differentiation, affects of sertoli cells
AMH causes leading cells to differentiate- produce testosterone (male duct system develops) or produce dihydrotestosterone ( penis, scrotum and access. sex glands develop)
Also cause degeneration of paramesonephric ducts
Female differentiation
specific genes on X chromosome cause ovaries to develop
no AMH
paramesonephric ducts become oviduct, uterus and part of vagina
complete female report tract
chromosomal sex
depends on sex chromosomes which are determined at time of fertilization
drives gonadal differentiation
gonadal and phenotypic sex
early stages are the same for both male and females
begin with undifferentiated precursor
precursor of gonad
gonadal ridge- swelling of body cavity and peritoneum
gonadal ridge= undifferentiated, biopotential, located next to mesonephros and mesonephric ducts
gametes
primordial germ cells- originate from yolk sac and migrate to the gonadal ridge
embryo proper
advanced embryo, not yet a fetus
gamete formation
yolk sac will decrease and allantois will increase in size
mesonephros
part of male reproductive system (duct)
paramesonephric duct
tubular system in females
gonadal ridge
precursor to gonad
primitive germ cells orginate in yolk sac and migrate to the gonadal ridge- organize into primitive sex cords
testis differentiation
Sry gene on sex determining region Y (and others on Y chromosome)
SRY protein (TDF-testis determining factor) initiates male sex determination
Ovarian differentiation
not default, requires two copies of key genes (Wnt4, Dax1, and FoxL2)
sex cords, testis differentiation
give rise to seminiferous tubules
sertoli cells- AMH, PGC give rise to spermatozoa eventually
Gonadal ridge, testis differentiation
leydig cells- testosterone
Ovarian development
absences of Sry and presence of other genes
sex cords regress
PGCs within follicles, on the surface of the ovary
PGCs give rise to oocytes
support and hormone producing cells- theca cells, granulosa cells
Tubular tract
both ducts present-Mesonephric (wolffian) and paramesonephric (Mullerian)
development depends on presence or absence of testicular hormones
Leydig cells
testosterone which is essential for development of mesonephric ducts
Sertoli cells
Anti Mullerian Hormones (AMH)
causes regression of the female (paramesonephric duct system)
mesonephrons
primitive kidney, if male orange tube regresses
Mesonephric/Wolffian ducts
epididymis, deferent ducts and urethran
Paramesonephric/Mullerian ducts
Oviducts, uterus, cervix and cranial vagina
Phenotypic sex
determined by hormones produced by gonad
Male: Testosterone and Dihydrotestosterone(DHT)
DHT= metabolite of testosterone- potent androgen
Genital tubercle
in presence of DHT develops into penis and in absence into clitoris
Genital swellings
DHT, develops into scrotum without into vulva
Genital Folds
DHT, folds close/fuse and in absence folds do not fuse
Disorders of Sexual Differentiation
can occur at any point in development
chromosomal, gonadal and phenotypic
Chromosomal disorders of sexual differentiation
usually originate from non disjunction of sex chromosomes or chromatids during meiosis or mitosis
nondisjunction
failure to separate chromosomes
Monosomy X
X0 chromosomal sex
tuners syndrome- gonadal sex= ovary or streak gonad
phenotypic sex is female
small statue
usually underdeveloped internal and external genitalia due to lack of 2nd X chromosome
usually sterile
Klinefelter’s Syndrome
XXY chromosomal sex
gonadal sex typically testes, often cryptorchid and phenotypically male
male due to presence of SRY
extra X chromosome leads to abnormal phenotype and usually sterile
common in ruminants
Trisomy X
chromosomal XXX
gonadal sex is ovaries and phenotypic sex= female
usually abnormal phenotype due to presence of extra X
Mosaics and chimeras
animals with more than one genetically distinct population of cells
Mosaic
all cells originate from single zygote
usually results from non disjunction during mitosis of early embryo
mosaic phenotype
depends on proportion of normal cells
large number of affected cells= embryonic death and most surviving Turners syndrome are mosaics
Chimera
contain cell lines originating from two diff. embryonic sources
experimentally or naturally occurring
Ex: geep, sheep and goat embryo fused
Freemartins
Chimera, most common in bovine
calf contains a portion of cells originating from its twin and is only clinically relevant when one is a male and other female
male and female characteristics with female tract underdeveloped
how to get a chimera
placenta from twin bovine pregnancies fuse and blood from the two fetuses mix
placental fusion occurs before gonadal differentiation and hormones are transferred between fetuses
T and DHT from male masculinize the female fetus to varying degrees
abnormalities of gonadal sex
occur when chromosomal sex and gonadal sex do not agree (SRY absent or nonfunctional)
sex reversals- XY sex reversed female so and XY with ovaries and an XX sex reversed male an XX with testes
sex reversed females
Y chromosome present but SRY non-functional
gonads often undifferentiated (streak gonads), phenotype female but not fully developed
sex reversed males
XX with testes
SRY positive, Sry translocated during crossing over (meiosis), differentiation proceeds in male direction due to functional SRY
SRY negative, mutation in gene downstream of SRY
Abnormalities of phenotypic sex
something not turned on or off, when chromosomal sex and gonadal sex do not agree with phenotypic sex, or phenotype is ambiguous
XX with ovaries, male or ambiguous; XY with testes, female or ambiguous phenotype
usually resulting from hormonal defect or hormone receptor defect
Testicular feminization
XY with testes, faulty androgen receptor
T and DHT cannot bind/exert effort which can affect testicular descent, formation of male tubular tract, external genitalia etc.
phenotype varies depending on severity of defect in receptor (vagina may be blind-ended, uterus hypo plastic, testes retained)
5-a-reductase deficiency
XY with testes but reduced ability to convert testosterone to DHT
testosterone level is high, external genitalia develop as female and underdeveloped mesonephric (wolffish) duct
Male pseudohermaphrodite
XY with testes, but female phenotype
Female Pseudohermaphrodite
XX with ovaries but male phenotype
much less common
ambiguous phenotype
have testes with female report organs finished
True hermaphrodite
both ovarian and testicular tissue present, 1 testes and 1 ovary
usually gonadal errors
1 testes with 1 ovotestis
1 ovary with 1 ovotestis
2 ovotestes
