In this case no sex linkage is involved a white-eyed fly is homozygous for the recessive allele at both loci. In order for any recessive trait to be expressed, it must be homozygous for that recessive trait. If an individual was heterozygous, the recessive allele would be masked by the dominant allele, giving it the dominant phenotype. Therefore, since white eyes are recessive, fruit flies with white eyes will always be homozygous aa for that recessive trait.
A fruit fly that is heterozygous Aa for this trait would have red eyes. Red is dominant A which means we can deduce that white is recessive a. Therefore AA individuals are red eye, and so to are Aa because the dominant red allele overrides the white recessive allele. Then the only way a fly can be white eyed is with aa. Both white eyed flies are aa so all four possible outcomes are aa in a single locus punnet square. Because red is dominant over white, in order for the flies to express the recessive white eye trait they must be homozygous for the recessive white allele - I.
If the question allows you to assume that eye-colour is a typical gene with two alleles, then we can figure out the answer. Dominant traits need only one dominant allele, so the genotype can be Aa or AA.
The only other combination is aa, and that codes for the recessive phenotype of white eyes. There can be no heterozygous white eyed fly.
Now see if you can figure out the ratio for each color. Mar 1, 5. Mar 2, 6. Moonbear , Mar 2, Mar 2, 7. Mar 2, 8. Mar 2, 9. Mar 2, Your name or email address: Do you already have an account?
We explain Punnett Square with video tutorials and quizzes, using our Many Ways(TM) approach from multiple teachers. This lesson will introduce how to use a punnett square to determine genetic traits.
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Homework 7 Assignment: Punnett Squares and Dihybrid Crosses Punnett Squares Complete the following by: 1. Filling out the punnett square 2. Describing each possible phenotype 3. Listing the probability for each genotype Note: remember that CAPITAL LETTER signifies a dominant trait and a lower case letter signifies a recessive trait%(2). With the results of the Punnett square, the probabilities of specific genotypes and phenotypes can be determined. Monohybrid Cross: Figure 1: Punnett squares showing a monohybrid cross between a) a homozygous dominant and homozygous recessive parent and b) heterzygous dominant parents.
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