12.3 Complex inheritance in Humans

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

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

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

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

Sex-linked traits Carried on sex chromosomes Color blindness Hemophilia

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

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