Lecture 7 Flashcards
primary sex determination
determination of the gonads
secondary sex determination
determination of the male and female phenotypes by the hormones produced by the gonads; male and female duct systems and external genitalia
both male and female gonads are formed by the same precursor…
bipotential gonad
in males, the Wolffian duct gives rise to…
testes, vas deferens, seminal vesicles, seminal glands, prostate
in females, the Mullerian duct gives rise to…
ovaries, fallopian tubes, uterus
Y chromosome houses…
SRY gene which contains genetic info for “maleness”
gonadal ridges form either ovaries or testes by what week?
5th week
gonadal differentiation in males stems from…
medulla
gonadal differentiation in females stems from…
cortex
Y chromosome carries SRY gene which encodes…
a TF that binds to certain regulatory regions of genes responsible for male characteristic development
SRY gene product has to function at a…
specific window of time to suppress ovary formation and promote testis formation
if SRY is activated, it will activate Sox9 which upregulates…
Fgf9 repressing Wnt4 expression -> leads to testis development
without SRY, what happens with Wnt4?
development of ovaries with help of Sox9, Fgf9
in an XX individual, the “pre-ovaries” produce estrogen which enables…
the Mullerian duct to form the uterus, oviducts, cervix, and upper portion of the vagina
in an XY individual, testes form via SRY and secrete…
MIH, and testosterone which activates the formation of the penis, male duct system, and inhibits development of breast primordia
androgen insensitivity
XY individual has mutation in testosterone receptor, but responds to estrogens made by adrenal glands
pseudoautosomal regions (PARs) are present on…
both ends of Y chromosome and share homology with regions on X chromosomes
PARs synapse and recombine with…
X chromosome during meiosis
the pairing region is critical for…
segregation of X and Y chromosomes during male gametogenesis
since the SRY is close to the PAR, you can sometimes get…
translocation of the SRY gene onto X chromosome leading to genetic female with male phenotype
how are genes in PARs inherited?
in an autosomal fashion because of crossing over
dosage compensation
females have potential to produce 2x as much product for X-linked genes
what does dosage compensation lead to?
a “genetic dosage” difference between genders
dosage compensation balances…
dose of X chromosome gene expression in males and females
what do females do that males don’t do to account for having two X chromosomes?
inactivate one, called Barr body
where are Barr bodies located?
against nuclear envelope of interphase cells
what happens if a Barr body is not unwound before mitosis?
subsequent cells will be missing an X chromosome
X-inactivation center (Xic) contains…
4 genes, including Xist and Tsix
genetic expression of Xic occurs only on…
inactivated X chromosome
inactivated X is coated by…
Xist RNAs
Tsix gene encodes a ncRNA that…
antagonizes Xist RNA
Drosophila have same sex chromosomes as humans but…
Y chromosome does not determine sex in Drosophila
do C. elegans have Y chromosomes?
NO
in Drosophila, sex is determined by…
ratio of X chromosomes to haploid sets of autosomes
if a fly has 3 sets of chromosomes and 2 X chromosomes, then…
the fly is a mosaic
in Drosophila, the Y chromosome contains genes for…
making sperm
threshold of maleness is reached when X:A ratio is…
1:2 (X:2A)
what does the presence of an additional X (XX:2A) result in?
female differentiation
C. Elegans 2 sexual phenotypes
males, hermaphrodites
C. elegans males
X0 - one X, no Y
C. elegans hermaphrodites have both…
testes and ovaries; XX
how do hermaphroditic C. elegans reproduce?
eggs are fertilized by stored sperm - self-fertilization
ZW sex determination system
condition where males are homogametic sex
in ZW animals, what determines sex of the offspring?
oocyte of the female (ZW) NOT sperm of the male (ZZ)
haplodiploid sex determination
males develop from unfertilized eggs; females from fertilized eggs
example of haplodiploid sex determined animal
Hymenoptera - queen mates once, uses that sperm all her life to produce female worker bees
Case I
low temps yield 100% females
Case II
high temps yield 100% females
Case III
low and high temps yield 100% females; medium temps yield males
critical period of incubation is known as the…
thermosensitive period (TSP)
effect of temp on aromatase
high temps lead to higher aromatase activity and vice versa; so higher temps means more conversion of androgens to estrogens like in Case II
sex-limited inheritance
expression of specific phenotype is limited to one sex
sex-influenced inheritance
sex of individual influences expression of phenotype
sex-influenced traits involves genes on…
autosomes not X or Y chromosomes
