Recitation 4 Gene factor of inheritance Example round vs wrinkled Alleles different versions of genes Example A or a Genotype the pair of alleles that you have Example Aa AA or aa Homozygous or heterozygous Phenotype physical trial Example round vs wrinkled Dominant or recessive Dominant round or recessive wrinkled True breeding homozygous for the allele in question Monohybrid crosses following one trait Dihybrid crosses following two traits Monohybrid examples Gene Big ears Mother AA little ears Father aa big ears Offspring Aa Imagine two heterozygotes All possible genotypes AA aA Aa aa Phenotypic ratio of 3 1 Dihybrid Cross Father has big ears and mother has little ears and all children have little ears We can deduce that little ears are the dominant A phenotype A little ears a big ears B little nose a big nose Example one AABB little little x aabb big big AaBb little little Example two AaBb little little x AaBb little little AABB aAbB AaBb aabb 9 A B 3A bb 3aaB 1aabb Monohybrid cross with two heterozygotes Genotypic ratio AA Aa aa 1 2 1 Phenotypic ratio A aa 3 1 Dihybrid cross with two heterozygotes Phenotypic ratio A B A bb aaB aabb 9 3 3 1
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