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AA X AA. A. A. AA. AA. A. A. AA. AA. Genotypic ratio: all AA. Phenotypic ratio: all red. AA X Aa. A. A. AA. AA. A. a. Aa. Aa. Genotypic ratio: 1AA:1Aa. Phenotypic ratio: all red. AA X aa. A. A. Aa. Aa. a. a. Aa. Aa. Genotypic ratio: all Aa.
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AA X AA A A AA AA A A AA AA Genotypic ratio: all AA Phenotypic ratio: all red
AA X Aa A A AA AA A a Aa Aa Genotypic ratio: 1AA:1Aa Phenotypic ratio: all red
AA X aa A A Aa Aa a a Aa Aa Genotypic ratio: all Aa Phenotypic ratio: all show dominant trait
Aa X Aa A a AA Aa A a aa Aa aa Genotypic ratio: 1 AA:2Aa:1aa Phenotypic ratio: 3 not red:1 red
Aa X aa A a Aa aa Aa a Aa a aa Aa Genotypic ratio: 1 Aa:1 aa Phenotypic ratio: 1 red: 1white
aa X aa a a aa aa a a aa aa Genotypic ratio: all aa Phenotypic ratio: all white
Complete Dominance vs. Incomplete Dominance • Most traits display complete dominance • the presence of one dominant allele masks the recessive allele • Some traits display incomplete dominance the heterozygous condition results in a separate phenotype, neither allele is completely dominant-they blend together • In some flowers, AA is red, Aa is pink, and aa is white
Codominance • Some traits are controlled by codominance: • both alleles for a gene are expressed in heterozygous offspring. • neither allele is dominant or recessive, nor do they blend; each is expressed equally. • the best example of this is in a horse’s coat color; heterozygous = roan color where they have both white and red hairs.
Dihybrid Cross • dihybridcross • between individuals with two pairs of traits.
Dihybrid Cross Rules • First figure out what the gametes are that the parents can make. Use the FOIL method to do this. Parents: AaBb X AaBb Gametes: AB, Ab, aB, ab X AB, Ab, aB, ab • Then place the gametes along the top and sides of the square and do the cross.
Dihybrid Cross Gametes from Parent One (Female) Gametes from Parent Two (Male)
Multiple Alleles • Several alleles exist for a trait
Sex Influenced Traits • Traits expressed differently in males and females • Example: baldness BB Bb bb male bald bald not bald bald not bald not bald female