Complex Inheritance of Human Traits

Codominance in Humans Phenotypes of both homozygotes are produced in the heterozygote Recall the checkered rooster Sickle-cell anemia

Sickle-cell Anemia Disorder where red blood cells are sickle shaped Normally concave Shorter life span and can slow bloodflow or block small vessels 1 in 12 African Americans is heterozygous for the disorder

Malaria Sickle Cell

Multiple Alleles in Humans Blood types Can be A, B, AB, or O

Type A The IA allele is dominant to i IAi or IAIA will give you type A blood Surface protein A is produced

Type B The IB allele is also dominant to i IBIB or IBi will =type B blood Surface protein B is produced.

Type AB The IA and IB alleles are codominant to each other IAIB you will have type AB blood Will produce both surface proteins

Type O The i allele is recessive Produces no surface molecule Homozygous ii you have blood type O

Sex-Linked Traits in Humans Traits that are determined by genes that are carried on the sex chromosomes Most of these genes are located on the X chromosome

Red-green Color Blindness People who have red-green color blindness can't differentiate these two colors

Hemophilia: An X-linked disorder Blood fails to clot normally because of a deficiency or abnormality of one of the clotting factors 1 male in every 10 000 has hemophilia but only about one in 100 million females Why?

Polygenic Inheritance in Humans These kinds of traits usually represent a range of variation that is measurable Color variations in human eyes Skin color

Changes in Chromosome Numbers Unusual numbers of autosomes Down syndrome: Trisomy 21 Unusual numbers of sex chromosomes Turner’s Syndrome and Klinefelter's Syndrome