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Chromosomes 2nd Exam > Sex Determination - Lecture 3 > Flashcards

Sex Determination - Lecture 3 Flashcards

1
Q

Germ Cells

A

Form from proximal epiblast
Earliest known marker is TNAP (tissue non-specific alkaline phosphatase) - but TNAP KO has no effect on germ cell formation
BMP4 and BMP8b appear to be essential in germ cell formation

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2
Q

Testicular Germ Cells

A

Testicular stem cells give rise to spermatocytes which undergo meiosis to become sperm

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3
Q

Alfred Jost experiments

A

Rabbits

  • Remove ovaries –> Female genital formation
  • Remove testes –>Wolffian regressian–> Female genital formation
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4
Q

WT1

A

Wilm’s tumor suppressor/activator gene

  • Mutations cause Frasier syndrome and Denys-Drash syndrome
  • Gonadal dysgenesis
  • Gonadoblastoma
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5
Q

SF1 Human KO

A

XY karyotype is phenotypically female

  • High ACTH, low cortisone, low aldosterone
  • Streaked gonads
  • Mullerian structures
  • Estrogen and progesterone induced menstruation
  • Adrenal hyperplasia
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6
Q

46, XX Males

A
  • Male external genitalia
  • Highly virilized
  • Sterile
  • Caused by fault recombination during paternal meiosis leading to SRY gene on X chromosome
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7
Q

46, XY Females

A
  • Pure gonadal dysgenesis
  • Streaked gonads
  • 30% experience gonadoblastoma or germinomas
  • Caused by SRY removal during XY interchange, Y lacks the SRY region
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8
Q

SRY

A

Sex-determining Region of the Y Chromosome

  • testes determining factor
  • only sex-determining region on the Y chromosome
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9
Q

Testes Determination Pathway

A

WT1 and SF1 —> SRY—>SOX9 —> Testes

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10
Q

WT1 and SF1

A

Sertoli and Leydig cell formation

Sertoli cells lead to production of Anti-Mullerian Hormone and spermatogenesis

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11
Q

SOX9

A
  • Mutations cause campomelic dysplasia (bone abnormalities)
  • 46, XY sex reversal with ambiguous genitalia
  • Death in neonatal period due to respiratory insufficiency
  • Autosomal dominant
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12
Q

AMH

A

Anti-mullerian hormone

  • secreted by sertoli/granulosa cells
  • causes regression of Mullerian derivatives
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13
Q

AMH Mutations

A
  • persistent Mullerian duct syndrome
  • Males with uterus and fallopian tubes
  • AMH Receptor mutations have same phenotypes
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14
Q

AHC (DAX-1)

A

X p21.3

  • Nuclear hormone receptor with DNA binding domain
  • Expressed in sertoli cells
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15
Q

AHC Mutations

A
  • Deletions cause congenital adrenal hyperplasia and hypogonadism
  • Duplications in XY individuals cause external female genitalia and impaired testicular development
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16
Q

WNT4 Mutations

A
  • Masculinized phenotype
  • Primary amenorrhea
  • Shortened vagina
  • Elevated testosterone levels
  • No uterus or fallopian tubes
  • Normal ovaries
  • Aplastic right kidney
17
Q

Types of Genital Ambiguity

A
  • True hermaphrodism - 46, XX with ovarian and testicular tissue
  • Female pseudohermaphrodism - 46, XX - internally female, externally male
  • Male pseudohermaphrodism - 46, XY - Male gonads, external female genitalia
18
Q

46, XX Ovotesticular Disorders of Sex Development

A

True hermaphrodism

  • Both ovarian and testicular tissue
  • Oocytes (not streaked ovaries) and testicles with spermatozoa
  • 70% have male external genitalia
  • 90% have uterus
  • Feminization at puberty
  • Some gonadal neoplasia
19
Q

46, XX Disorders of Sex Development

A

Female pseudohermaphrodism
-21-hydroxylase deficiency
OR
-11 beta-hydroxylase deficiency

20
Q

21-Hydroxylase Deficiency

A
  • Causes female pseudohermaphrodism
  • Ambiguous genitalia
  • Uterus and ovaries are normal
  • Salt wasting (life threatening)
  • Detected by: Elevated 17-alpha OH progesterone (shows a block in the enzymatic pathway)
  • Treatment: Cortisol, mineral corticoids
21
Q

11 beta-hydroxylase deficiency

A
  • Causes female pseudohermaphrodism
  • Ambiguous genitalia
  • Hypertension due to salt retention
  • Detected by: Elevated deoxycortisol and deoxycorticotestosterone
  • Treated by: Cortisol
22
Q

Aromatase Deficiency

A
  • Clitoral hypertrophy
  • XX and XY can be affected
  • Delayed epiphyseal closure
  • Primary amenorrhea
  • KEY SYMPTOM: Virilization of pregnant mother
  • Autosomal recessive
  • Treatment: Estrogen
23
Q

Teratogenic 46, XX Disorders of Sex Development

A
  • If mother is given androgens during pregnancy, fetus may become virilized
  • Much less frequent now than in the past
24
Q

46, XY Disorders of Sex Development

A 
Male pseudohermaphrodism
Caused by:
-45,X/46,XY mosaicism
-Testicular biosynthetic errors
-5 alpha-reductase deficiency
-Complete or partial androgen insensitivity
-Agonadia
-Leydig cell agenesis
25
Q

45,X/46,XY Mosaicism

A

Causes male pseudohermaphrodism

  • Variable phenotype - Female genitalia –> Ambiguous genitalia
  • Uterus is usually present
  • Increased risk for gonadal neoplasia
  • Most cases in neonatal show female or ambiguous genitalia
  • Most cases in utero show male genitalia
26
Q

5 alpha-reductase deficiency

A

Causes male pseudohermaphrodism

  • Enzyme block at conversion of testosterone to dihydrotestosterone (DHT)
  • Normal male levels of testosterone but low levels of DHT
  • Can have male, female, or ambiguous genitalia
  • Increased T/DHT ratio
  • Autosomal recessive
  • Often raised as girls, wind up as male gender idenity, masculinize with puberty
27
Q

Partial androgen insensitivity

A

Causes male pseudohermaphrodism

  • Variable extent of genital virilization: labial fusion, clitoral hypertrophy, hypospadias
  • Feminization at puberty despite T levels higher than normal XY individuals
  • Caused by: Mutations in androgen receptor may still allow for some binding leading to incomplete virilization
28
Q

Complete androgen insensitivity

A

Causes male pseudohermaphrodism

  • 46, XY individuals have bilateral testes
  • Female external genitalia
  • Blind ending vagina (no uterus or cervix)
  • No mullerian derivatives
  • Cells unable to respond to testosterone
  • Well developed breasts
  • 5% develop gonadal neoplasia
29
Q

Ovarian maintenance determinants

A
  • Xp11
  • Xq13
  • BMP15 gene (only expressed in oocytes)
  • FMR1 (Fragile X)
  • POF1B (premature ovarian failure region)
  • PGMRC1 (progesterone membrane receptor)
30
Q

BMP15

A

SHEEP
-Heterozygotes have increased fertility
-Homozygotes have decreased fertility
Human mutants are infertile

31
Q

FMR1 - Fragile X

A
  • Intellectual disability
  • Normal range 5-54 CGG repeats
  • Premutation range 54-200 CGG repeats (infertile)
  • Mutation range 200+ repeats (fertile)
  • 10-15% of premutation carriers have POF
32
Q

FSH Mutations

A

Follicule stimulating hormone (and receptor)

  • Primary amenorrhea
  • Infertility
  • Small ovaries and uterus
  • Autosomal recessive

Chromosomes 2nd Exam (10 decks)

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