Sex Determination and Sex-Linked Traits Chapter 4

Outline Sex Determination Different Karyotypes sry gene and maleness Sex Linked Traits Barr Bodies

1. Chromosomal Sex determination Systems XX-XO XX-XY ZZ-ZW Haplodiploidy

A closer look at 2 different systems of sex determination

2. Genetic Sex Determining Systems Genic Balance Sex Determination Environmental Sex Determination drosophila Slipper limpet

Drosophila: genic balance Sex chromosome Autosome* complement X:A ratio Phenotype XX and AA 1.0 female Xy and AA 0.5 male XXY and AA XXX and AAA 0.67 intersex * autosome= any non-sex chromosome

Human Karyotypes Klinefelter Syndrome Non-disjunction NORMAL Turner Syndrome

Maleness Determination of maleness is due to sry gene of Y chromosome Expression of gender is more complex than just sry gene. Example: androgen insensitivity Xy genotype Many female characteristics!

Sex Linked (X-linked) Traits (3 examples) Human Color Blindness

Sex Linked (X-linked) Traits White eye Drosophila

Pedigree of hemophilia XhY x XHXh ½ XH ½ Xh ¼ XHXh ¼ XhXh ½ Xh ½ Y ¼ XHY ¼ XhY

Barr Bodies & X-Inactivation What are they? Why does it occur?

Number of Barr Bodies in Human Cells

X-Inactivation in cats Tortoiseshell Color

Y-Linked Inheritance Few genes on Y chromosomes Few examples of known Y linked traits to date

The End