1. COMPLEX INHERITANCE OF HUMAN TRAITS
Chapter 12.3

2. CODOMINANCE IN HUMANS SICKLE CELL ANEMIA
If homozygous, red blood cells take on a “sickle” shape
If heterozygous, person will produce both normal and sickle shaped red blood cells
Sickle cell cause
slow blood flow
Block small vessels
Result in tissue damage and pain

3. MULTIPLE ALLELES AND BLOOD TYPE
ABO BLOOD GROUP
Type A, Type B, Type AB, Type O
Controlled by 3 alleles
IA, IB, I
Blood typing is necessary for blood transfusions
So the body doesn’t “reject” the blood
Blood typing is also used to determine paternity of a child

5. SEX-LINKED HUMAN TRAITS
Most genes are located on the X chromosome
X-LINKED RECESSIVE TRAITS
Red-green color blindness
hemophilia

6. Red-Green Color Blindness
Caused by inheritance of a recessive allele on the X chromosome
People can’t identify red and green traffic lights by color

7. Hemophilia
X linked recessive disorder that causes your blood to not be able to clot
Cuts take a long time to stop bleeding
Females need 2 recessive alleles to show trait, males only need 1

8. POLYGENIC INHERITANCE IN HUMANS
Skin Color

9. CHANGES IN CHROMOSOME NUMBER
ABNORMAL NUMBER OF AUTOSOMES
Extra autosomes = “trisomy”
Instead of having 46 chromosomes, they would have 47
Results from “nondisjunction” during meiosis
Failure of homologous chromosomes to separate
Karyotype:
chart of chromosome pairs used to identify unusual chromosome numbers in a cell

11. Down Syndrome: Trisomy 21
The ONLY autosomal trisomy which doesn’t result in death
3rd chromosome present in 21st pair
Incidence of this increases in mothers that give birth over age 40

12. Abnormal # of Sex Chromosomes
XO (Missing X chromosome)
XXX, XXY, or XYY
As long as there is 1 Y chromosome, the child will be a male
Extra 23rd pair chromosomes
People lead normal lives, however, they can’t have children and some have varying degrees of mental retardation