1. 12.3 Complex inheritance in Humans

2. Complex inheritance Codominance Multiple alleles Sex-linked traits
Polygenic inheritance
Changes in chromosome number

3. Codominance
Phenotypes of both homozygotes produced in the heterozygote
Sickle cell anemia is an example in humans
Heterozygous people have both normal and sickle cells
Resistant to malaria

4. Codominance 1 in 12 African Americans have sickle cell anemia
Hemoglobin differs by one amino acid
Causes red blood cells to be sickle shaped
Slow blood flow, block small blood vessels

5. Multiple alleles More than two alleles for a trait Human blood type
Three alleles IA, IB, I
Blood types A, AB, B, O
Match for compatibility
Identify parent

6. Sex-linked traits Carried on sex chromosomes Color blindness
Hemophilia

7. Polygenic inheritance
Traits determined by more than one gene
Often see trait as range of variation
Skin color
Eye color

8. Changes in chromosome number
Karyotype is used to look at chromosome numbers
Unusual number of autosomes
Trisomy 21, Down syndrome
Unusual number of sex chromosomes
XO, XXX, XXY, XYY
Most lead normal lives but cannot have children, some have mental disabilities