In fish of the species Perissodus microlepis, some individuals have mouths that open to the right and some individuals have mouths that open to the left. The direction of the mouth opening is a genetic trait controlled by a single gene. The allele for a right-opening mouth (R) is dominant to the allele for a left-opening mouth (r). If two fish heterozygous for the mouth trait are crossed, what is the expected ratio of phenotypes in the offspring?

Question

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When two heterozygous individuals (Rr) are crossed, the expected genotype ratio is 1:2:1 (RR:Rr:rr), which translates to a phenotype ratio of 3 right-opening mouths (RR and Rr) to 1 left-opening mouth (rr), since the right-opening mouth allele (R) is dominant over the left-opening mouth allele (r).

In Fish of the Species Perissodus Microlepis, Some Individuals Have