1. CHAPTER 12 SEX-LINKED TRAITS

2. Karyotype: a picture of chromosomes.

3. Body Cells vs. Sex Cells
Autosomes: the first 22 homologous pairs of chromosomes.
Autosomes are the same for both males and females.
Sex cells: Determine sex of offspring

4. Is it Male or Female? Explain

5. Sex chromosomes: determines the sex of the individual.
The sex chromosomes are the 23rd pair of chromosomes. 
XX =female

6. XY=male

7. Which parent determines the sex of an offspring?
DAD
Why?
All moms have the genotype XX. When egg cells are made, they will all carry a single X chromosome.

8. All dads have the genotype XY
All dads have the genotype XY. When sperm cells are made, 50% will have an X chromosome and 50% will have a Y chromosome.
Therefore, males and females are born in roughly a 50:50 ratio.

9. SEX-LINKED TRAITS
Those traits that are controlled by genes on the X or Y chromosomes.
NOTE: The Y chromosome is much smaller than the X chromosome and only contains a few genes. Most sex-linked traits are on the X chromosome.

10. XH Xh XH XH XH Xh XH Y XH Y Xh Y male
In humans, hemophilia is a sex-linked trait.  Having hemophilia is recessive (Xh) to being normal (XH). The heterozygous female is called a carrier.  Cross a carrier female with a normal male. XH Xh
__ XHXh __  X  __ XHY ___
XH XH
XH Xh XH Y
male
XH Y
Xh Y

11. Results: Genotypic ratio: 1 XHXH :1 XHXh : 1 XHY :1 Xh Y
Phenotypic ratio: 2 normal females: 1normal male:
1 male with hemophilia XH Y
XH XH
Normal Female
XH Xh
Normal Female
Xh Y
Male w/ hemophilia
XH Y Normal Male

12. Now You Try Cross a carrier female with a male with hemophilia.
__ XHXh __  X  __ XhY ___

13. Results: Genotypic ratio: 1 XHXh :1 XhXh : 1 XHY :1 Xh Y
Phenotypic ratio: 1 normal female:
1 female w/ Hemopholia:
1normal male:
1 male with hemophilia
Xh Xh
Female w/ hemophilia Xh Y
XH Xh
Normal Female
Xh Y
Male w/ hemophilia
XH Y Normal Male

14. Genetic Sex-Linked Disorders Color Blindness
Cause: x-linked recessive
1/10 males have, 1/100 females have. Why the difference?
Individuals are unable to distinguish shades of red-green.
                                          

15. Genetic Sex-Linked Disorders
2- Hemophilia A and B
Recessive disorders that affect 1 of 5,000 males. These interfere with normal blood clotting and occur on the X chromosome.

16. Using Fruit Flies to Study Genetics
Thomas Hunt Morgan, 1908
Among normal red-eyed Drosophila he found a mutated white-eyed fly (male).
Since it was a recessive gene that was expressed only in male flies, Morgan suggested that the chromosome was located on the X chromosome.
Miniature winged mutation was transmitted on the same gene. These two characteristics did not always travel together.
Morgan suggested that the chromosomes could swap parts and received the Nobel prize in 1934.

17. Drosophila melanogaster

18. X-linked Inheritance
A situation where the genes that cause a disorder are located on the X chromosome.
More male victims than female
Hemophilia
Color-blindness
Duchenne muscular dystrophy

19. Polygenic Inheritance
Traits that are influenced by several Genes.
Show many degrees of variation.
Examples:
Height
Hair color
Skin Color
Eye Color