Transcription
Sex DeterminationRead pp65-75 in text
Outline1.Different mechanisms for sexdetermination2. Mammalian Y chromosome3. SRY4. Testosterone
Chromosomal sex determination inmammals and fliesXXXYmammalsfemalemaleDrosophilafemalemale
Sex is determined differentlyin mammals and osophilafemalemalemalefemalemale
Mechanisms of sex determinationChromosomal sex determination:In flies and mammals females are the homogametic sex (XX) andmales the heterogametic sex (XY).In butterflies and birds males are the homogametic sex (ZZ) andfemales the heterogametic sex (ZW).Drosophila melanogaster (fruit fly)XX females; XY malesX:autosome ratio determines sex1.0 female; 0.5 maleMammalsThe single Y-linked gene SRY determines the male phenotype.
Environmental sex determinationIn some reptiles, the temperature of embryonicdevelopment determines sex.
Clownfish live in small groupsinhabiting a single anemone.The group consist of abreeding pair, which cohabitwith a few non-reproductive,smaller male clownfish. Whenthe female dies, the dominantmale changes sex and becomesthe female.
Outline1.Different mechanisms for sexdetermination2. Mammalian Y chromosome3. SRY4. Testosterone
The Y chromosome is necessary andsufficient for male development!But what on Y is important for maledevelopment?
The Y chromosome is a wasteland;it contains very few genes.Which one controls maleness.
Outline1.Different mechanisms for sexdetermination2. Mammalian Y chromosome3. SRY4. Testosterone
SRY is both necessary and sufficientfor male development
SRY is a transcription factor
Indifferent gonadSRYTestesno SRYOvaries
Outline1.Different mechanisms for sexdetermination2. Mammalian Y chromosome3. SRY4. Testosterone
SryTestes form from gonadTestosteroneanti-Mullerian hormoneMullerian ducts degenerate
Testosterone (steroid) and anti-Mullerian hormone (peptide)both regulate transcriptionAMHreceptorSteroids are lipid soluble and can pass throughthe plasma membrane. Their receptors are inthe cell.Peptide hormones cannot pass through theplasma membrane. Their receptors are in thecell membrane.
Testes5 alpha reductase
Sry OFFOvaries form from gonadNo AMHNo testosteroneMullerian ductsWollfian ductsdegenerateInternal female structuresOviduct, cervix, uterus, upper vaginaNo DHTExternal female structuresUterus, lower vagina,clitoris, labia
In butterflies and birds males are the homogametic sex (ZZ) and females the heterogametic sex (ZW). Drosophila melanogaster (fruit fly) XX females; XY males X:autosome ratio determines sex 1.0 female; 0.5 male Mammals The single Y-linked gene SRY determines the male phenotype. Environmental sex determination In some reptiles, the temperature of embryonic development determines sex. Clownfish .
