February 4th, 2009 What is the genetic structure of human variation? Polymorphism Refers to the presence of 2 or more separate phenotypes for a certain gene in the population. Human blood type. ABO blood group system Each person has one of 4 blood types. A, B, AB, O Complications to Mendalian inheritance. Polygenic Traits Determined by more than 1 pair alleles. Eye color, hair color, height, skin color, etc. Pleiotropy Single allele can have multiple effects. Heritability For some traits, only some of the genetic variation can be calculated. Heritability ranges from 0 ? 1. 0 = non-genetic; 1 = all genetic Only heritable traits respond to natural selection. Measurement of heritability is complicated by pleiotropy. Incomplete Dominance A heterozygous individual may manifest an intermediate state. Co-dominance of Alleles. Two alleles can be co-dominant Both are expressed No intermediate form is expressed AB blood type expresses both A and B characteristics
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