lecture 7 Flashcards
primary sex determination
determination of gonads
secondary sex determination
determination of male and female phenotypes by the hormones produces by the gonads, and the formation of the male and female duct systems and external genitalia
what are the male and female gonads formed from?
the biopotential gonad
what houses the genetics information for “maleness”?
the Y chromosome
what is the early embryo considered?
hermaphroditic
how many weeks does it take to form either ovaries or testes from the biopotential gonads?
5 weeks
what does the SRY gene encode?
transcription factor that organizes bipotential gonads into testes
does the SRY gene have a certain window of time it needs to function in?
yes
what does the “pre-ovaries” produce?
estrogen
what does estrogen do for the pre-ovaries?
enables the mullerian duct to form the uterus, oviducts, cervix, and the upper portion of the vagina
AMH
mullerian inhibiting factor
what does AMH do?
destroys the mullerian duct
what do the testes secrete?
AMH and testosterone
testosterone
activates the formation of the penis, male duct systems, and inhibits the development of breast primordia
what is an androgen insensitivity?
when a person has the SRY gene but has a mutation in the testosterone receptor which allows them to respond to estrogen; causes female phenotype.
PARs
pseudoautosomal regions
where are PARs located?
on both ends of the Y chromosome, share homology with regions on the X chromosome
when can PARs recombine with the X chromosomes?
meiosis
pairing region
critical for segregation of X and Y chromosomes during male gametogenesis
how are genes within PARs inherited?
in an autosomal fashion
dosage compensation
females may produce twice as much product for x-linked genes
what can dosage compensation cause?
genetic dosage between genders
barr bodies
compensates for X chromosome dosage disparities
where are barr bodies located?
lies against nuclear envelope of interphase cells
what do barr bodies help with?
dosage compensation
Xic
contains 4 genes including Xist and Tsix
where is the Xic gene located?
on the inactivated X chromosome
Xist
RNAs that coat the inactivated X chromosome
Tsix gene
encodes a ncRNA and antagonizes Xist RNA
what sex chromosomes do drosophila have?
same as humans (XX for females, XY for males)
does the Y chromosome determine sex in drosophila
no
what type of drosophila do not have Y chromosomes
C. elegans
how is sex determined in drosophila?
ratio of X chromosomes to autosomes , 2 for females, 1 for males
what does 3 sets of autosomes and 2 X chromosomes mean in drosophila?
the fly is a mosaic
what is the genetic balance theory?
threshold of maleness is reached when the ratio is X:A
what are the 2 sexual phenotypes for C. elegans?
males (1 X chromosome) and hermaphrodites (2 X chromosomes)
ZW sex determination system
where males are the homogametic sex
what cell determines the sex of offspring in the ZW system?
oocyte
who follows the ZW sex determination system?
birds, snakes, and moths
how many sex chromosomes do those in the monotreme system have?
10
haplodiploid sex determination
males develop from unfertilized eggs and females come from fertilized eggs
what follows the haplodiploid sex determination?
hymenoptera, thrips
case I of temperature sex determination
low temperature produce 100% females
case II of temperature sex determination
high temperatures produce 100% females
case III of temperature sex determination
low and high temperatures produce 100% females, but intermediate temperatures produce males
what species are temperature sex determination seen in?
crocodiles, turtles, and lizards
thermosensitive period
critical period of incubation
what has a profound influence on sex determination in reptiles?
environment, temperature, and enzymes which can be inhibited by temperature
aromatase
coverts androgens into estrogens
