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VET 410: Reproduction > Reproductive System Development > Flashcards

Reproductive System Development Flashcards

1
Q

is sex a genotype or phenotype

A

phenotype

affected by genetics and environment

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2
Q

what is clinical sex determined by

A

gonadal histology
(histological testes = male, ovaries = female)

NOT chromosome karyotype

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3
Q

what are the levels of sex determination

A
  1. chromosomal
  2. gonadal
  3. fetal somatic sex (internal, external)
  4. hypothalamic differentiation
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4
Q

chromosomal sex determination

A

first level of sex determination based on chromosomal karyotype

determines gonadal development (predicts sex, does NOT define it)

XX: female
XY: male

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5
Q

gonadal sex determination

A

development of ovaries (F) or testes (M)

clinically defines sex

can get aneuploidies (sex chromosome variants) or sex reversal

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6
Q

sex chromosome variants/aneuploidies

A

XXY –> testes (M)
XO –> ovaries (F)

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7
Q

sex reversal

A

chromosomal sex does NOT match gonadal sex

SRY negative XY individuals with ovaries
- caused by a missing SRY region on Y chromosome (results in failed development of testes but does NOT direct the development of ovaries)
- requires active FOXL2 gene (directs ovary development)

SRY negative XX individual with testes
- mechanism unknown

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8
Q

internal somatic sex determination

A

development of paramesonephric ducts (F) or mesonephric ducts (M)

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9
Q

how does internal sex determination in males occur

A
  1. testes produce AMH & testosterone
  2. AMH binds AMH-R on paramesonephric ducts –> stimulates regression of PM ducts
  3. testosterone binds AR on mesonephric ducts –> stimulates survival of M ducts
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10
Q

how does internal sex determination occur in females

A
  1. ovaries do not produce AMH or testosterone
  2. lack of AMH binding to AMH-R on paramesonephric ducts –> stimulates survival of PM ducts
  3. lack of testosterone binding to AR on mesonephric ducts –> stimulates regression of M ducts
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11
Q

AMH

A

anti mullerian hormone

synthesized by Sertoli cells in the testes to induce regression of the Mullerian (paramesonephric) ducts

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12
Q

testosterone

A

synthesized by Leydig cells in the testes to stabilize Wolffian (mesonephric) ducts and direct development of the epididymis, ductus deferens, and accessory sex glands

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13
Q

do males, females, or both express AMH and androgen receptors on parameso/mesonephric ducts

A

BOTH - the presence or absence of AMH and testosterone determines regression or stabilization of ducts

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14
Q

external somatic sex determination

A

development of a clitoris and vagina (F) or penis, prepuce, and scrotum (M)

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15
Q

how does external somatic sex determination occur in males

A
  1. testes produce testosterone
  2. testosterone gets converted into DHT by 5a-reductase
  3. DHT stimulates migration of the genital tubercle
  4. results in development of male external genitalia
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16
Q

how does external somatic sex determination occur in females

A
  1. ovaries do not produce testosterone
  2. no conversion to DHT
  3. lack of DHT causes no migration of genital tubercle
  4. results in development of female external genitalia
17
Q

5a-reductase

A

enzyme that converts testosterone into DHT (a more potent androgen), which directs genital tubercle migration

conversion occurs in genital tubercle and perineal skin of the fetus

18
Q

do males, females, or both express 5a-reductase and androgen receptors

A

BOTH - if females exposed to testosterone, will get conversion to DHT and subsequent development of male external genitalia

19
Q

hypothalamic differentiation of sex determination

A

estradiol positive feedback (F) or loss of estradiol feedback (M) that gets organized during fetal development and gets activated after birth (at puberty)

20
Q

stages of gonadal development

A
  1. primordial germ cells migrate from yolk sac –> fetus –> gonadal ridge (both cortex and medulla)
  2. signaling directs proliferation of PGCs in either the cortex OR medulla, and other PGCs regress
  3. germ cells multiply via mitosis into spermatogonia or oogonia
  4. development of ducts and genitalia occurs as directed by testes/lack of testes
21
Q

what gonads develop if PGCs in the cortex proliferate

A

ovary

22
Q

what gonads develop if PGCs in the medulla proliferate

A

testes

23
Q

is the gonadal ridge differentiated when PGCs migrate into it

A

NO - undifferentiated

PGCs migrate into both cortex and medulla

24
Q

true hermaphrodite

A

has both ovarian and testicular tissue

(rare in most species)

25
Q

pseudohermaphrodite

A

internal or external genital development does NOT correspond with gonadal sex
(ex. testes w/ PM ducts, ovaries w/ M ducts, testes w/ vagina, ovaries w/ penis)

UNRELATED TO KARYOTYPE

26
Q

freemartin calves

A

female pseudohermaphrodite (ovaries w/ mesonephric ducts)

male and female twins in one uterus –> males express AMH and testosterone –> travels through placental vascular anastomosis to the female –> binds to female AMH-R and ARs –> stabilizes female M ducts

27
Q

androgen resistance syndrome

A

male pseudohermaphrodite
(testes w/o mesonephric ducts)

lack of a functional androgen receptor –> doesn’t recognize testosterone binding in a male –> regression of M and PM ducts

AR gene is X-linked (XfY males will have undescended testes with neither M or PM ducts)

28
Q

true sex reversal

A

XX with testes
XY with ovaries

29
Q

atypical phenotypes

A

when phenotype at one level is discordant with karyotype or phenotype at another level

  • chromosomal karyotype: sex reversal
  • gonadal phenotype: pseudohermaphrodite
  • somatic phenotype: true hermaphrodite, Turner’s syndrome, or Klinefelter syndrome

VET 410: Reproduction (24 decks)

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