1. Sex Determination and Sex-Linked Traits
Chapter 4

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

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

4. A closer look at 2 different systems of sex determination

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

6. 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

7. Human Karyotypes Klinefelter Syndrome Non-disjunction NORMAL
Turner Syndrome

8. 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!

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

10. Sex Linked (X-linked) Traits
White eye Drosophila

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

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

13. Number of Barr Bodies in Human Cells

14. X-Inactivation in cats
Tortoiseshell Color

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

16. The End