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M2M Genetics > Determination of Sex and Disorders of Sex Chromosomes > Flashcards

Determination of Sex and Disorders of Sex Chromosomes Flashcards

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Biology 101 flashcards
1
Q

Why is sexual reproduction advantageous?

A

speeds evolution and contributes to increased survival among species by increasing genetic variability

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2
Q

what is X chromosomal inactivation?

A

one X chromosome in females is inactivated randomly. only one X chromosome is active in all people males and females

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3
Q

what does X inactivation in females cause?

A

females are mosaic for which X is expressed (maternal or paternal)

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4
Q

what determines which X chromosome will be inactivated?

A

expression of the XIST gene on chromosome that will be inactivated

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5
Q

where is the XIST gene located?

A

on chromosome that will be inactivated, not present on active chromosome

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6
Q

what does the XIST gene produce?

A

non-coding RNA product that binds to inactive X chromosome

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7
Q

what is a Barr body?

A

inactive X chromosome

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8
Q

what does expression of XIST allow for?

A

allows for DNA methylation and histone modification to deactivate chromosome

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9
Q

when does X inactivation occur?

A

1st week of embryogenesis

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10
Q

how many genes on the X chromosome escape inactivation?

A

10-15%

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11
Q

where are the genes located on the X chromosome that escape inactivation?

A

the p arm

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12
Q

why are the genes that “escape” inactivation important?

A

because they could have greater clinical significance than those on Xq

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13
Q

what is nonrandom X inactivation?

A

if there is structural abnormality in X chromosome, that chromosome will be selected for inactivation

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14
Q

what happens to an X chromosome that has a balanced translocation with an autosome?

A

it will remain activated even though structural abnormality because doesn’t want to inactivate the autosome

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15
Q

what are the 3 steps of sex differentiation?

A
  1. genetic sex determination
  2. gonad formation
  3. internal and external reproductive organs
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16
Q

how is the genetic sex determined?

A

XX female
XY male
absence of some genes from Y chromosome initiates female phenotype

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17
Q

what gene is responsible for inducing development of the testes?

A

SRY gene (sex-determining region on Y)

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18
Q

what happens if the SRY gene is absent or not expressed?

A

female gonads form

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19
Q

where is the WT gene located and what does it do?

A

chromosome 11

directs differentiation of the mesonephros and genital ridge

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20
Q

where is the SOX9 gene located and what does it do?

A

chromosome 17

codes for transcription factors that induce differentiation of Sertoli and Leydig cells

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21
Q

what other genes does SOX9 work with?

A

SF1 and SRY

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22
Q

where is steroidogenic factor 1 (SF1) located and what does it do?

A

chromosome 9

induces differentiation of sertoli and leydig cells

23
Q

what does SRY do to SF1?

A

upregulates expression

24
Q

what X chromosome gene induces ovarian development?

A

DAX1

25
Q

what disorder does duplication of DAX1 lead to?

A

Dosage sensitive sex reversal (DSS)

26
Q

what regulates the formation of internal and external genitalia?

A

testosterone and Mullerian inhibiting substance (MIS)

27
Q

what 2 structures do both males and females have internally initially?

A

mesonephric and paramesonephric ducts

28
Q

what do the testes do during internal genitalia development?

A

produce mullerian inhibiting substance (MIS) which causes regression of paramesonephric ducts. Testosterone then stimulates development of mesonephric duct into epididymis and ductus deferens

29
Q

What occurs in the absence of MIS and testosterone?

A

mesonephric duct degenerates, paramesonephric duct becomes fallopian tubes, uterus, and upper vagina

30
Q

What is the determining factor of the external genitalia formation?

A

the presence of testosterone
+ testosterone = penis and scrotum
- testosterone = external features of vagina

31
Q

what does the genital tubercle differentiate into?

A

male: glans and shaft of penis
female: glans and shaft of clitoris

32
Q

what does the definitive urogenital differentiate into?

A

male: penile urethra
female: vestibule

33
Q

what does the urethral fold differentiate into?

A

male: penis
female: labia minora

34
Q

what does the labioscrotal fold differentiate into?

A

male: scrotum
female: labia majora

35
Q

what disease is caused by this karyotype? 45X

A

Turner Syndrome

1 in 2000-5000

36
Q

what are the clinical characteristics of turner syndrome?

A
  • develop of females
  • gonadal dysgenesis
  • short stature
  • coarctation of aorta
37
Q

what disease is caused by this karyotype? 47 XXY

A

Klinefelter syndrome

1 in 1000

38
Q

what are the clinical characteristics of Klinefelter syndrome?

A
  • develop as males
  • gonadal dysgenesis
  • tall stature
  • impulsive behavior
39
Q

what disease is caused by this karyotype? 47 XYY

A

47 XYY syndrome

1 in 900-1000

40
Q

what are the clinical characteristics of 47 XYY syndrome?

A

exceptionally tall, otherwise normal males

41
Q

what is the karyotype of intersex (true hermaphrodite)?

A

XX, XY mosaicism most common

42
Q

what is are the clinical characteristics of intersex?

A

ovarian and testicular tissues

43
Q

what is the karyotype of sex reversal disorder?

A

XX males or XY females

44
Q

what are the clinical characteristics of sex reversal disorder?

A

gonadal sex is opposite of genetic sex

45
Q

what is the karyotype for intersex (pseudohermaphroditism)?

A

XY males and XX females (normal karyotype)

46
Q

what are the clinical characteristics of intersex psuedohermaphroditism?

A

genital sex at odds with genetic sex

47
Q

what is testicular feminization?

A

there is androgen insensitivity

48
Q

what is congenital adrenal hyperplasia?

A

excessive androgen production, autosomal recessive condition affecting 1 in 25000

49
Q

what is salpha deficiency?

A

autosomal recessive, failure to convert testosterone to dihydrotestosterone

50
Q

what does dihydrotestosterone do?

A

necessary for activation in development of external genitalia

51
Q

what is leydig cell hypoplasia?

A

autosomal recessive, lack of testosterone production from defect in lutenizing hormone receptor

52
Q

what is Smith-Lemli-Opitz syndrome?

A

autosomal recessive, defect in cholesterol synthesis leading to decreased testosterone synthesis

53
Q

what is Kallman syndrome?

A

autosomal recessive or X-linked, gonadotropin deficiency leading to hypogenitalism in males

M2M Genetics (10 decks)

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