Sex determination in non-mammalian vertebrates

Question 1

List 4 key differences between sex determination in birds and mammals

Answer 1

1. In birds, despite also using a genetic sex determination system, the females are heterogametic, ZW and the males are homogametic ZZ.
2. Gonad identity is influenced by the presence of oestrogen and testosterone.
   * Whereas in mammals, primary sex determination occurs to specify the gonad as either testis or ovaries and it then differentiates accordingly producing oestrogen/testosterone to promote secondary sex determination, in non-mammalian vertebrates including birds, oestrogen and testosterone are involved in primary sex determination/specifying the fate of the gonad.
3. The DMRT1 gene on the Z chromosome is a dosage-dependent sex determining gene.
4. Sex determination in somatic cells is partly autonomous in chickens = bilateral gynandromorph.

Question 2

What is the difference between sex-determination in birds and xenopus?

Answer 2

Whilst both use a genetic sex determination system whereby the males are homogametic ZZ and females are heterogametic ZW…
In birds, it is a dosage-dependent mechanism, the Z chromosome contains the DMRT1 gene which activates testis-specific gene expression and 2 copies are needed to repress FoxL2 and CYP19A1 and activate Sox9 and AMH.
Whereas in xenopus, it isn’t the number of Zs but the presence of a W because the W encodes the dm-w gene, a DMRT-1 like gene that has the DNA-binding domain (DM-domain) but has lost the transactivation domain so it competes for binding of the same genes as DMRT1 but doesn’t activate any gene expression thus acting to prevent expression of genes involved in testis-differentiation.

Question 3

What kind of sex determination system is used by the tongue sole?

Answer 3

ZW/ZZ, males are homogametic, the sex-determining gene is DMRT1 on the Z chromosome, probably dose-dependent mechanism, 2 copies of DMRT1 makes a male and 1 copy of DMRT1 makes a female.

Question 4

What kind of sex determination system is used by oryzias latipes?

Answer 4

XX/XY, males are heterogametic, there is a gene on the Y chromosome called dmy that acts a binary switch (a bit like mammals) that promotes maleness.

Question 5

What kind of sex determination system is used by oryzias dancena?

Answer 5

XX/XY, the Y chromosome has an additional regulatory element for the Sox3 gene causing expression in the gonad.

Question 6

What kind of sex determinnation system is used by oryzias luzonensis?

Answer 6

XX/XY, the Y chromosome has the gsdfy gene, a TGF-beta paracrine factor involved in sex determination.

Question 7

What kind of sex determination system is used by the patagonian pejerrey?

Answer 7

XX/XY, the Y chromosome has the amhy gene, a Y chromosome homologue of AMH.

Question 8

What kind of sex determination system is used by takifugu rubripes?

Answer 8

XX/XY, the Y chromosome carries the AMH receptor Amhr2 as a sex-determining gene.

Question 9

What kind of sex determination system is used by the rainbow trout?

Answer 9

XX,XY, the Y chromosome has a homologue of the IRF9 (interferon regulatory factor 9 gene) called sdy which has lost its DNA-binding domain but forms a complex with FoxL2 preventing FoxL2 from activating the aromatase gene thus preventing oestrogen being synthesised.