Consider the production of flower color in the Japanese...

Consider the production of flower color in the Japanese morning glory (Pharbitis nil). Dominant alleles of either of two separate genes $(A /-\cdot b / b \text { or } a / a \cdot B /-)$ produce purple petals. $A /-\cdot B /-$ produces blue petals, and $a / a \cdot b / b$ produces scarlet petals. Deduce the genotypes of parents and progeny in the following crosses: $$\begin{array}{cll} \text { Cross } & \text { Parents } & \text { Progeny } \\ \hline 1 & \text { blue } \times \text { scarlet } & \frac{1}{4} \text { blue }: \frac{1}{2} \text { purple : } \frac{1}{4} \text { scarlet } \\ 2 & \text { purple } \times \text { purple } & \frac{1}{4} \text { blue }: \frac{1}{2} \text { purple }: \frac{1}{4} \text { scarlet } \\ 3 & \text { blue } \times \text { blue } & \frac{3}{4} \text { blue }: \frac{1}{4} \text { purple } \\ 4 & \text { blue } \times \text { purple } & \frac{3}{8} \text { blue }: \frac{4}{8} \text { purple }: \frac{1}{8} \text { scarlet } \\ 5 & \text { purple } \times \text { scarlet } & \frac{1}{2} \text { purple }: \frac{1}{2} \text { scarlet } \\ \hline \end{array}$$

Consider the production of flower color in the Japanese morning glory (Pharbitis nil). Dominant alleles of either of two separate genes $(A /-\cdot b / b \text { or } a / a \cdot B /-)$ produce purple petals. $A /-\cdot B /-$ produces blue petals, and $a / a \cdot b / b$ produces scarlet petals. Deduce the genotypes of parents and progeny in the following crosses:
$$\begin{array}{cll}
\text { Cross } & \text { Parents } & \text { Progeny } \\
\hline 1 & \text { blue } \times \text { scarlet } & \frac{1}{4} \text { blue }: \frac{1}{2} \text { purple : } \frac{1}{4} \text { scarlet } \\
2 & \text { purple } \times \text { purple } & \frac{1}{4} \text { blue }: \frac{1}{2} \text { purple }: \frac{1}{4} \text { scarlet } \\
3 & \text { blue } \times \text { blue } & \frac{3}{4} \text { blue }: \frac{1}{4} \text { purple } \\
4 & \text { blue } \times \text { purple } & \frac{3}{8} \text { blue }: \frac{4}{8} \text { purple }: \frac{1}{8} \text { scarlet } \\
5 & \text { purple } \times \text { scarlet } & \frac{1}{2} \text { purple }: \frac{1}{2} \text { scarlet } \\
\hline
\end{array}$$

Key Concepts

Digenic Inheritance

Digenic inheritance refers to a genetic scenario in which two distinct genes jointly determine a single phenotypic trait. In this type of inheritance, both gene loci contribute to the outcome, and the specific combination of alleles at both loci dictates the phenotype. This requires analyzing how alleles from each gene interact together, rather than considering each gene’s effect in isolation.

Gene Interaction

Gene interaction encompasses the various ways in which multiple genes can affect a single trait. It is not simply an additive effect; rather, genes may modify, enhance, or mask the effects of one another. In complex traits, different gene products may interact in pathways or networks leading to diverse phenotypes, which is critical when predicting outcomes from genetic crosses.

Epistasis

Epistasis is the phenomenon where the phenotypic effect of one gene is influenced by one or more other genes. This can result in non-Mendelian ratios, as the presence of certain alleles at one gene locus can mask or modify the expression at another locus. Understanding epistasis is essential to deciphering how combinations of alleles from separate genes lead to unique trait expressions.

Dominance and Recessiveness

Dominance and recessiveness are fundamental concepts in genetics that describe the relationship between alleles. A dominant allele will typically express its phenotype even in the presence of a recessive allele, which is masked in such heterozygous combinations. This principle is essential for deducing genotypes from observed phenotypes and for predicting the outcomes of crosses.

Phenotypic Ratio Analysis

Phenotypic ratio analysis involves comparing the proportions of different observable traits in offspring to infer underlying genetic mechanisms. By analyzing these ratios, one can deduce the likely genotypes of both parents and progeny. This method is particularly useful in complex breeding scenarios where multiple genes interact to produce differing phenotypes.

Transcript

00:01 Told that these different combinations of alleles would result in these three different colors of flower, blue, purple, and scarlet.

00:07 We are now given five different crosses in the results and want to determine the genotype of those crosses.

00:14 So the first cross is blue and scarlet, and we get a ratio of one -fourth blue, one -half purple, and one -fourth scarlet.

00:21 So since we know that blue has to have some combination, has to have some kind of dominant for both alleles, this means that we have a blank, b, blank, where both of our alleles are dominant.

00:34 Meanwhile, for scarlet, we know that it's homozygose recessive for both alleles.

00:38 Tested if our blue was heterozygose dominant for both alleles.

00:43 We were to cross these via punnet squares, we would get the same ratio of one -fourth blue, two -fourths purple, and one -fourth scarlet.

00:52 So that means that our genotype for blue is heterozygose -dominant for both, and homozygose -rethrozygose -remonent for both, recessive for scarlet.

01:01 Told that these different, our next crosses between purple, purple, getting one -fourth blue, one -half purple, and one -fourth scarlet.

01:09 And again, as we know, the given genotype's is that only one of the alleles will be dominant, whether it's homozygos or heterozygose.

01:18 So let's just do a test cross between a guess of we have a dominant a but recessive b and a recessive a but a dominant b...

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