Sex Chromosomes Flashcards
If Y chromosome is present…
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
sertoli cells of the early testis
produces Mullerian Inhibiting Factor
acts upon the paramesonephric ducts (Mullerian ducts) to cause their regression
external male sex organs is in response to what
3-alpha-dihydrotestosterone
made from testosterone by 5-alpha-reductase
If no Y chromosome is present…
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
lyonization
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
male pseudohermaphrodite
genetically male (has Y)
external genitalia fail to develope
female pseudohermaphrodite
genetically female (no Y)
external genitalia fail to develope
true hermaphrodite
both ovarian and testicular tissue
types of Turner’s Syndrome
45, X, i(Xq) = classic
46, XX, Xp- = short stature, congenital malformations
46, XX, Xq- = gonadal dysfunction
symptoms of Turner’s Syndrome
cystic hydromas
short stature
cardiac and renal abnormalities
average intelligence (not retard)
no secondary sexual characteristics
treatment of Turner’s Syndrome
estrogen
progesterone
growth hormone
Klinefelter Syndrome
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
treatment for Klinefelter
testosterone
47, XYY
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
trisomy X
47, XXX
birth = normal female,
development: tall, low IQ
puberty = normal
reproduction = many infertile, not a higher risk for aneuploid children
androgen insensitivity
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
gonadal carcinoma
existence of poorly differentiated gonadal tissue in an intraabdominal environment increases risk
Fragile X Syndrome
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
diagnosis of Fragile X
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
glans –>
penis or clitoris
labioscrotal folds –>
scrotum or labia majora
Classic Hemophilia
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
Sherman Paradox in Fragile X
expansion of trinucleotide repeats occurs readily from female to son
expansion less common when male to daughter transmission
