Get Calculating Mendel's Ratios Answers

A 3:1 Ratio is the relative fraction of phenotypes among progeny (offspring) results following mating between two heterozygotes, where each parent possesses one dominant allele (e.g., A) and one recessive allele (e.g., a) at the genetic locus in question—the resulting progeny on average consist of one AA genotype (A ...

What does a 3:1 phenotypic ratio look like? This will occur when two heterozygous parents each give one allele to their offspring, creating two possible phenotypes even though there may be multiple genotypes. It is important to note that genotypic and phenotypic ratios will not always be the same.

This 9:3:3:1 phenotypic ratio is the classic Mendelian ratio for a dihybrid cross in which the alleles of two different genes assort independently into gametes. Figure 1: A classic Mendelian example of independent assortment: the 9:3:3:1 phenotypic ratio associated with a dihybrid cross (BbEe × BbEe).

Normally, we should expect a 1 : 1: 1:1 ratio in a testcross if independent assortment takes place. But actually, we get a 7: 1: 1:7 ratio, this indicates that dominant alleles are having a tendency to remain together. Similarly was the case with recessive alleles also.

The F2 generation always produced a 3:1 ratio where the dominant trait is present three times as often as the recessive trait. Mendel coined two terms to describe the relationship of the two phenotypes based on the F1 and F2 phenotypes.

A cross of two F1 hybrids, heterozygous for a single trait that displays incomplete dominance is predicted to give a 1:2:1 ratio among both the genotypes and phenotypes of the offspring.

The normal ratio from selfing dihybrid is 9:3:3:1, but epistatic interactions of the C and P genes will give a modified 9:7 ratio. The following table describes the interactions for each genotype and how the ratio occurs.

This 9:3:3:1 phenotypic ratio is the classic Mendelian ratio for a dihybrid cross in which the alleles of two different genes assort independently into gametes. Figure 1: A classic Mendelian example of independent assortment: the 9:3:3:1 phenotypic ratio associated with a dihybrid cross (BbEe × BbEe).

Such gene interaction is known as duplicate genes with cumulative effect. If the dominant condition (either homozygous or heterozygous) at either locus (but not both) produces the same phenotype, the F2 ratio becomes 9: 6: 1.