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Animation: Cross of One Character in "MendAliens"

by Pearson
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Let's examine the inheritance of eye color in MendAliens. Black eyes are the wild type. However, some MendAliens have orange eyes. If we make a cross between these parental aliens, all of the F1 generation will have black eyes due to this cross. What does this tell you about the relationship between the allele for black eyes and the allele for orange eyes? What eye colors do you expect to see in offspring of an F1 x F1 cross? In the F2 generation, the phenotypic ratio is approximately 3 black-eyed to 1 orange-eyed, or, stated another way, three-quarter black to one-quarter orange. The simplest explanation is that there is one gene involved and that the allele for orange eyes is recessive to the allele for black eyes. To interpret the results, if we use the symbol small b for the orange allele and capital B for the black, which is the wild type allele, we can follow the cross. Next, let's make the cross between two F1 individuals. The F2 genotypes are one BB to two Bb to one bb. Only two phenotypes are seen because B is dominant to b, so both BB and Bb genotypes have the dominant phenotype. A three to one phenotypic ratio is the result of crossing two heterozygotes where one allele is completely dominant to the other allele. The three to one phenotypic ratio derives from a one to two to one genotypic ratio of homozygote for the dominant allele to heterozygote to homozygote for the recessive allele. The orange eyes are explained by a single gene with the orange allele being recessive to the normal black allele. This monohybrid cross illustrates Mendel's law of segregation.
Let's examine the inheritance of eye color in MendAliens. Black eyes are the wild type. However, some MendAliens have orange eyes. If we make a cross between these parental aliens, all of the F1 generation will have black eyes due to this cross. What does this tell you about the relationship between the allele for black eyes and the allele for orange eyes? What eye colors do you expect to see in offspring of an F1 x F1 cross? In the F2 generation, the phenotypic ratio is approximately 3 black-eyed to 1 orange-eyed, or, stated another way, three-quarter black to one-quarter orange. The simplest explanation is that there is one gene involved and that the allele for orange eyes is recessive to the allele for black eyes. To interpret the results, if we use the symbol small b for the orange allele and capital B for the black, which is the wild type allele, we can follow the cross. Next, let's make the cross between two F1 individuals. The F2 genotypes are one BB to two Bb to one bb. Only two phenotypes are seen because B is dominant to b, so both BB and Bb genotypes have the dominant phenotype. A three to one phenotypic ratio is the result of crossing two heterozygotes where one allele is completely dominant to the other allele. The three to one phenotypic ratio derives from a one to two to one genotypic ratio of homozygote for the dominant allele to heterozygote to homozygote for the recessive allele. The orange eyes are explained by a single gene with the orange allele being recessive to the normal black allele. This monohybrid cross illustrates Mendel's law of segregation.