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Animation: Testcross in "MendAliens"

by Pearson
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Now let's cross a different set of parents that have the same phenotypes as the parents in the cross we just analyzed. However, just because they have the same phenotypes doesn't mean they have the same genotypes. We must analyze the F1 generation to help us understand the genetics. If we use B for the black or wild type allele and b for the orange allele, can you give the genotypes of the parents and the offspring? We know that the genotype of the orange-eyed individuals is bb. The orange-eyed offspring must have received a small b allele from each parent, so the black-eyed parent must be Bb. The black-eyed offspring must have received a b allele from the orange-eyed parent and a B allele from the black-eyed parent. The cross of an individual with a dominant phenotype to a homozygous recessive individual in order to find out its genotype is called a testcross. There are two possible outcomes of a testcross. As highlighted on the left, if all the F1 offspring have the dominant phenotype, then the genotype of the parent with the dominant phenotype is homozygous dominant, BB in this example. As highlighted on the right, if half of the F1 offspring have the dominant phenotype and half have the recessive phenotype, then the genotype of the parent with the dominant phenotype is heterozygous, Bb in this example.
Now let's cross a different set of parents that have the same phenotypes as the parents in the cross we just analyzed. However, just because they have the same phenotypes doesn't mean they have the same genotypes. We must analyze the F1 generation to help us understand the genetics. If we use B for the black or wild type allele and b for the orange allele, can you give the genotypes of the parents and the offspring? We know that the genotype of the orange-eyed individuals is bb. The orange-eyed offspring must have received a small b allele from each parent, so the black-eyed parent must be Bb. The black-eyed offspring must have received a b allele from the orange-eyed parent and a B allele from the black-eyed parent. The cross of an individual with a dominant phenotype to a homozygous recessive individual in order to find out its genotype is called a testcross. There are two possible outcomes of a testcross. As highlighted on the left, if all the F1 offspring have the dominant phenotype, then the genotype of the parent with the dominant phenotype is homozygous dominant, BB in this example. As highlighted on the right, if half of the F1 offspring have the dominant phenotype and half have the recessive phenotype, then the genotype of the parent with the dominant phenotype is heterozygous, Bb in this example.