BIOL 2107 Lecture Notes - Lecture 5: Zygosity, Wild Type, Anemia
30 Jan 2017
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Document Summary
A dihybrid cross produces parental types and recombinant types. Each f1 dihybrid produces four possible gametes in a 1:1:1:1 ratio: yy rr 1/4 y r, 1/4 y r, 1/4 y r, 1/4 y r. Four phenotypic classes occurred in the f2 progeny: two are like parents, two are recombinant. Some phenotypic variation poses a challenge to mendelian analysis. Example: lentils come in an array of colors and patterns: crosses of pure-breeding lines can result in progeny phenotypes that don"t appear to follow mendel"s rules. Explanations for some traits: no definitively dominant or recessive allele, more than two alleles exist, multiple genes involved, gene-environment interactions. Dominance is not always complete: incomplete dominance i. e. snapdragon flower color, codominance i. e. lentil coat patterns, ab blood group in humans. A gene may have >2 alleles i. e. lentil coat patterns, abo blood groups in humans, histocompatibility in humans.
