HUMAN GENETICS

1. HUMAN GENETICS All the rules for genetics also apply to human beings. However, humans are harder to study for genetics • Humans are not sexually mature for 12-18 years • Humans only have 1-3 offspring at a time, and most humans only have 1-5 offspring • At any one time, only 2 or 3 generations are alive.

2. Special circumstances • X linked genes Most genes are found on the autosomes (chromosomes 1-22). Some genes are found on the X chromosome. In these cases, they are expressed differently in men than in women.

3. HEMOPHILIA Hemophilia is a disease where a person is unable to stop bleeding from a cut. It is a recessive gene on the X chromosome. Males inherit hemophilia differently from females.

4. MALES XH Y this is a male without hemophilia (dominant) Xh Y this is a male with hemophilia (recessive) A man inherits hemophilia from his mother (why?)

5. FEMALES XHXH this is a female without hemophilia. She cannot pass hemophilia to her children. XHXh this is a female without hemophilia. She can pass hemophilia to her children. XhXh this is a female with hemophilia.

6. Assume a woman heterozygous for hemophilia marries a man without hemophilia? Write parental genotypes: woman: XHXh man: XHY

7. PUNNETT SQUARE XH Xh XHXH XH XHXh XHY Y XhY

8. None of the daughters have hemophilia. Half of the sons have hemophilia.