Sex Determination

Question 1

3 stages of sexual differentiation

Answer 1

chromosome (XX, XY)
Gonadal (testes or ovaries)
Phenotypic (male or female characteristics)

each stage depends on previous

Question 2

Male differentiation

Answer 2

Sex determining region (SRY protein/ TDF)
testes develop
sertoli cells secrete anti mullerian hormone (AMH)

Question 3

Male differentiation, affects of sertoli cells

Answer 3

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

Question 4

Female differentiation

Answer 4

specific genes on X chromosome cause ovaries to develop
no AMH
paramesonephric ducts become oviduct, uterus and part of vagina
complete female report tract

Question 5

chromosomal sex

Answer 5

depends on sex chromosomes which are determined at time of fertilization

drives gonadal differentiation

Question 6

gonadal and phenotypic sex

Answer 6

early stages are the same for both male and females

begin with undifferentiated precursor

Question 7

precursor of gonad

Answer 7

gonadal ridge- swelling of body cavity and peritoneum

gonadal ridge= undifferentiated, biopotential, located next to mesonephros and mesonephric ducts

Question 8

gametes

Answer 8

primordial germ cells- originate from yolk sac and migrate to the gonadal ridge

Question 9

embryo proper

Answer 9

advanced embryo, not yet a fetus

Question 10

gamete formation

Answer 10

yolk sac will decrease and allantois will increase in size

Question 11

mesonephros

Answer 11

part of male reproductive system (duct)

Question 12

paramesonephric duct

Answer 12

tubular system in females

Question 13

gonadal ridge

Answer 13

precursor to gonad

primitive germ cells orginate in yolk sac and migrate to the gonadal ridge- organize into primitive sex cords

Question 14

testis differentiation

Answer 14

Sry gene on sex determining region Y (and others on Y chromosome)

SRY protein (TDF-testis determining factor) initiates male sex determination

Question 15

Ovarian differentiation

Answer 15

not default, requires two copies of key genes (Wnt4, Dax1, and FoxL2)

Question 16

sex cords, testis differentiation

Answer 16

give rise to seminiferous tubules

sertoli cells- AMH, PGC give rise to spermatozoa eventually

Question 17

Gonadal ridge, testis differentiation

Answer 17

leydig cells- testosterone

Question 18

Ovarian development

Answer 18

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

Question 19

Tubular tract

Answer 19

both ducts present-Mesonephric (wolffian) and paramesonephric (Mullerian)

development depends on presence or absence of testicular hormones

Question 20

Leydig cells

Answer 20

testosterone which is essential for development of mesonephric ducts

Question 21

Sertoli cells

Answer 21

Anti Mullerian Hormones (AMH)

causes regression of the female (paramesonephric duct system)

Question 22

mesonephrons

Answer 22

primitive kidney, if male orange tube regresses

Question 23

Mesonephric/Wolffian ducts

Answer 23

epididymis, deferent ducts and urethran

Question 24

Paramesonephric/Mullerian ducts

Answer 24

Oviducts, uterus, cervix and cranial vagina

Question 25

Phenotypic sex

Answer 25

determined by hormones produced by gonad Male: Testosterone and Dihydrotestosterone(DHT) DHT= metabolite of testosterone- potent androgen

Question 26

Genital tubercle

Answer 26

in presence of DHT develops into penis and in absence into clitoris

Question 27

Genital swellings

Answer 27

DHT, develops into scrotum without into vulva

Question 28

Genital Folds

Answer 28

DHT, folds close/fuse and in absence folds do not fuse

Question 29

Disorders of Sexual Differentiation

Answer 29

can occur at any point in development chromosomal, gonadal and phenotypic

Question 30

Chromosomal disorders of sexual differentiation

Answer 30

usually originate from non disjunction of sex chromosomes or chromatids during meiosis or mitosis

Question 31

nondisjunction

Answer 31

failure to separate chromosomes

Question 32

Monosomy X

Answer 32

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

Question 33

Klinefelter's Syndrome

Answer 33

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

Question 34

Trisomy X

Answer 34

chromosomal XXX gonadal sex is ovaries and phenotypic sex= female usually abnormal phenotype due to presence of extra X

Question 35

Mosaics and chimeras

Answer 35

animals with more than one genetically distinct population of cells

Question 36

Mosaic

Answer 36

all cells originate from single zygote | usually results from non disjunction during mitosis of early embryo

Question 37

mosaic phenotype

Answer 37

depends on proportion of normal cells large number of affected cells= embryonic death and most surviving Turners syndrome are mosaics

Question 38

Chimera

Answer 38

contain cell lines originating from two diff. embryonic sources experimentally or naturally occurring Ex: geep, sheep and goat embryo fused

Question 39

Freemartins

Answer 39

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

Question 40

how to get a chimera

Answer 40

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

Question 41

abnormalities of gonadal sex

Answer 41

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

Question 42

sex reversed females

Answer 42

Y chromosome present but SRY non-functional gonads often undifferentiated (streak gonads), phenotype female but not fully developed

Question 43

sex reversed males

Answer 43

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

Question 44

Abnormalities of phenotypic sex

Answer 44

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

Question 45

Testicular feminization

Answer 45

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)

Question 46

5-a-reductase deficiency

Answer 46

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

Question 47

Male pseudohermaphrodite

Answer 47

XY with testes, but female phenotype

Question 48

Female Pseudohermaphrodite

Answer 48

XX with ovaries but male phenotype much less common

Question 49

ambiguous phenotype

Answer 49

have testes with female report organs finished

Question 50

True hermaphrodite

Answer 50

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