Sex determination notes

Sex determination notes - Sex-linked genes on the X...

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Sex-linked genes on the X chromosome Males are hemizygous—They have one allele. Whatever allele they have will show up. Hemophilia- Lack clotting factor 8 Duchenne Muscular dystrophy- heterozygous females are okay, but males are not—they start off okay, but it sets in eventually, usually by 12 or 14. You’d see it only in males. This is because it’s recessive on the x. Becker’s MD- Those kids generally survive. Most births with MD are new mutations. Sex Determination Nondisjunction In a female, you could get eggs that have XX or no X (O). This happens when the chromosomes go to the same pole instead of opposite poles. If fertilized, you could get XXX XO (1 X) XXY Or just Y—does not survive In a male, you could get an 0 or a YY. When fertilized, you could get a XYY. 45 XO—Turner’s syndrome (or just Turner’s). Occurs about 1 in 2,500-5000 live female births. Classified as female. It is estimated that 99% of the XO conceptions abort spontaneously—most don’t survive to term. Phenotype untreated—very small stature, sloping neck, “shield” chest, stubby fingers, sometimes some internal abnormalities. Most are in the normal IQ range, like the normal population, but there’s pretty good IQ. Not as good at 3D rotation problems. 77% of the time, the single X came from the egg, so it was the sperm that didn’t
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Sex determination notes - Sex-linked genes on the X...

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