Sex Chromosomes

Question 1

If Y chromosome is present…

Answer 1

SrY gene

primitive gonad develops male structures (testis)

Leydig cells of the testis secretes testosterone that causes the mesonephric ducts (Wolffian ducts) to differentiate into male structures
- vas deferens
- epididymis
etc

Question 2

sertoli cells of the early testis

Answer 2

produces Mullerian Inhibiting Factor

acts upon the paramesonephric ducts (Mullerian ducts) to cause their regression

Question 3

external male sex organs is in response to what

Answer 3

3-alpha-dihydrotestosterone

made from testosterone by 5-alpha-reductase

Question 4

If no Y chromosome is present…

Answer 4

early gonad becomes the ovary

lack of testosterone…allows mesonephric duct regression

no Mullerian Inhibiting Factor…allows paramesonephric duct differentiation

• uterus
• fallopian tubes
• upper 1/3 of vagina

lack of testosterone –> prevents the external structures from developing into the male phenotype

Question 5

lyonization

Answer 5

2 weeks after fertilization

one of the X chromosomes in each cell of embryo becomes inactive

in normal tissue, random

abnormal X is usually preferentially inactivated

if some of a autosome is attached to X (translocation) - that one is preserved so that the autosome material remains active

Question 6

male pseudohermaphrodite

Answer 6

genetically male (has Y)

external genitalia fail to develope

Question 7

female pseudohermaphrodite

Answer 7

genetically female (no Y)

external genitalia fail to develope

Question 8

true hermaphrodite

Answer 8

both ovarian and testicular tissue

Question 9

types of Turner’s Syndrome

Answer 9

45, X, i(Xq) = classic

46, XX, Xp- = short stature, congenital malformations

46, XX, Xq- = gonadal dysfunction

Question 10

symptoms of Turner’s Syndrome

Answer 10

cystic hydromas

short stature

cardiac and renal abnormalities

average intelligence (not retard)

no secondary sexual characteristics

Question 11

treatment of Turner’s Syndrome

Answer 11

estrogen

progesterone

growth hormone

Question 12

Klinefelter Syndrome

Answer 12

47, XXY (15% mosaic)

mechanism = nondisjunction

half lost due to miscarriage…if born = normal male

development:

• normal…tall and thin
• slightly more dumb…behavioral problems
• small testis, hypogonadism

infertile

Question 13

treatment for Klinefelter

Answer 13

testosterone

Question 14

47, XYY

Answer 14

paternal nondisjunction

prenatal = genetic counseling dilemma??

birth = normal male, development = tall, behavioral problems

puberty is normal

normal reproduction….not a higher risk for aneuploid children

Question 15

trisomy X

Answer 15

47, XXX

birth = normal female,

development: tall, low IQ

puberty = normal

reproduction = many infertile, not a higher risk for aneuploid children

Question 16

androgen insensitivity

Answer 16

46, XY

defect: no androgen receptor in target cells

inheritance = X-linked

birth = normal female (look for testis/hernia)

development =

• feminization
• incomplete adrenarche
• amenorrhea
• small clit/labia
• lower 2/3 of vagina –> absent uterus and tubes and mesonephric structures

Question 17

gonadal carcinoma

Answer 17

existence of poorly differentiated gonadal tissue in an intraabdominal environment increases risk

Question 18

Fragile X Syndrome

Answer 18

X linked mental retardation

more common in males

Xq27.3 fragiel site

abnormal amount of trinucleotide (CGG) repeats at Xq27.3 site

premutation = 52-200

female meiosis tends to increase the number of repeats from premutation to full mutation (not male)

so premutation female material is more likely to expand to mutation than a premutation male

severity of disease increases with generation

Question 19

diagnosis of Fragile X

Answer 19

old method = cytogenetic
- grow on folate deficient media to induce fragile break sites

new method

a. southern anaylsis….separates the trinucleotide repeat segments based on size
b. PCR will give size of mutation (best for premutation)
* *best do both

Question 20

glans –>

Answer 20

penis or clitoris

Question 21

labioscrotal folds –>

Answer 21

scrotum or labia majora

Question 22

Classic Hemophilia

Answer 22

Factor VIII deficiency

gene for Factor VIII is on X chromosome

men are symptomatic since they only have 1 X

women are rarely
…1% have skewed inactivation
–> will have massive bleeding during menstruation and excessive surgical bleeding

Question 23

Sherman Paradox in Fragile X

Answer 23

expansion of trinucleotide repeats occurs readily from female to son

expansion less common when male to daughter transmission