12.3 Complex inheritance in Humans

Complex inheritanceCodominanceMultiple allelesSex-linked traitsPolygenic inheritanceChanges in chromosome number

CodominancePhenotypes of both homozygotes

produced in the heterozygote Sickle cell anemia is an example in

humansHeterozygous people have both

normal and sickle cellsResistant to malaria

Codominance1 in 12 African Americans have

sickle cell anemiaHemoglobin differs by

one amino acidCauses red blood cells

to be sickle shapedSlow blood flow,

block small blood vessels

Multiple allelesMore than two alleles for a traitHuman blood type

Three alleles IA, IB, IBlood types A, AB, B, OMatch for compatibilityIdentify parent

Sex-linked traitsCarried on sex chromosomesColor blindnessHemophilia

Polygenic inheritanceTraits determined by more than

one geneOften see trait as range of

variationSkin colorEye color

Changes in chromosome numberKaryotype is used to look at

chromosome numbersUnusual number of autosomes

Trisomy 21, Down syndromeUnusual number of sex chromosomes

XO, XXX, XXY, XYYMost lead normal lives but cannot have children, some have mental disabilities