Mammals: which is homogametic and heterogametic sex
Homo is female = xx
Hetero is male = xy
Rely on x inactivation
Birds : which is homo and hetero gametic sex
Male is homo = zz
Female is hetero = zw
Not z inactivation, but chromosomal dosage dependent
What is sex determining region in avians
DMRT1
need double dosage of this to be male
Ancestral role of testosterone
Normal maturation of male germ cells
Behavioural role of testosterone
Activates male specific Beh
Directly via androgen receptors or indirectly via local conversion to oestrogen
Mammalian XX and XY are not homologous to avian ZZ and ZW
What does that mean
even though both systems determine sex using two different chromosomes, they evolved independently and are not derived from the same ancestral chromosome pair.
What region on avian chromosome involved with female determination
Short arm of the W chromosome
What human chromosome is Z syntenic with
9
And has gene blocks from 5 8 and 18
Gonadal formation in male chickens
Double dose of z chromosome means bilateral testes formation, intrabdominal for aerodynamic purposes
Gonadal formation in female chickens
Monolateral, one ovary on left side
Also for aerodynamic purposes
Dual ducts system in avian
Wolffian and mullerian same as in mammals
Female right ovary produces AMH and kills itself basically
Males AMH is active and Müllerian ducts are suppressed, wolffian ones develop
What does overexpression of dmrt1 cause in female chicks
Testicular formation
How do we know that 12 wired bird of paradise plumage development is a primary genetic mechanism
Castration has no effect
Develops as a consequence of chromosomal sex, not cuz of testosterone
In peacocks how does castration affect plumage
Doesn’t affect the plumage but affects plumage display
What did fernando nottenohm discover about canaries
They have discrete brain areas for song learning and song production
Where is vocal motor control of canneries lateralised to
Left motor nerve
Beh dimorphism in singing in zebrafinch
Male birds will Sing females will chatter
Anatomical dimorphism in zebrafish in singing (ie what area of brain curcial for singing)
Robustus archistristum (RA)
Larger in males
what hormone promotes axonal growth and development of a large RA region
oestrogen
what happens to neurons in female brain from Higher vocal centre
held in a “holding pattern”
non-functional circuit
doesnt form synapses with the RA
becasue no exposure to oestrogen
where does neo natal sex steroids in the zebrafinches come from, how do we know
castration = no effect on sexually dimorphism of brain
and also central aromatase levels are low
they hae neuronal synthesised oestrogen
what is eclipse state
Eclipse state is when breeding season is over, the plumage goes away and they get duller and more female like
it is oestrogen driven in seasonal dimorphic birds
what do gynandromorphic birds show us
sex determination is not via systemic hormones - they wouldve acted on all tissues both sides
it must be cell-autonomous and gene dosage dependent
