The normal color of snapdragons is red. Some pure lines...

The normal color of snapdragons is red. Some pure lines showing variations of flower color have been found. When these pure lines were crossed, they gave the following results (see the table): $$\begin{array}{clll} \text { Cross } & {}{} {\text { Parents }} & {}{} {\mathrm{F}_{1}} & {}{} {\mathrm{F}_{2}} \\ \hline 1 & \text { orange } \times \text { yellow } & \text { orange } & 3 \text { orange }: 1 \text { yellow } \\ 2 & \text { red } \times \text { orange } & \text { red } & 3 \text { red }: 1 \text { orange } \\ 3 & \text { red } \times \text { yellow } & \text { red } & 3 \text { red }: 1 \text { yellow } \\ 4 & \text { red } \times \text { white } & \text { red } & 3 \text { red }: 1 \text { white } \\ 5 & \text { yellow } \times \text { white } & \text { red } & 9 \text { red: } 3 \text { yellow: } 4 \text { white } \\ 6 & \text { orange } \times \text { white } & \text { red } & 9 \text { red: } 3 \text { orange: } 4 \text { white } \\ 7 & \text { red } \times \text { white } & \text { red } & 9 \text { red: } 3 \text { yellow: } 4 \text { white } \\ \hline \end{array}$$ a. Explain the inheritance of these colors. b. Write the genotypes of the parents, the $\mathrm{F}_{1}$, and the $\mathrm{F}_{2}$

The normal color of snapdragons is red. Some pure lines showing variations of flower color have been found. When these pure lines were crossed, they gave the following results (see the table):
$$\begin{array}{clll}
\text { Cross } & {}{} {\text { Parents }} & {}{} {\mathrm{F}_{1}} & {}{} {\mathrm{F}_{2}} \\
\hline 1 & \text { orange } \times \text { yellow } & \text { orange } & 3 \text { orange }: 1 \text { yellow } \\
2 & \text { red } \times \text { orange } & \text { red } & 3 \text { red }: 1 \text { orange } \\
3 & \text { red } \times \text { yellow } & \text { red } & 3 \text { red }: 1 \text { yellow } \\
4 & \text { red } \times \text { white } & \text { red } & 3 \text { red }: 1 \text { white } \\
5 & \text { yellow } \times \text { white } & \text { red } & 9 \text { red: } 3 \text { yellow: } 4 \text { white } \\
6 & \text { orange } \times \text { white } & \text { red } & 9 \text { red: } 3 \text { orange: } 4 \text { white } \\
7 & \text { red } \times \text { white } & \text { red } & 9 \text { red: } 3 \text { yellow: } 4 \text { white } \\
\hline
\end{array}$$
a. Explain the inheritance of these colors.
b. Write the genotypes of the parents, the $\mathrm{F}_{1}$, and the
$\mathrm{F}_{2}$

Key Concepts

Dihybrid Cross and Segregation Ratios

A dihybrid cross involves two different gene loci and is used to study the interaction between them. The modified segregation ratios (such as 3:1 or 9:3:4) seen in the F2 generation are indicative of more complex genetic interactions than single-gene inheritance, demonstrating how combinations of alleles across two loci can produce different phenotypic outcomes in the offspring.

Mendelian Inheritance

This concept refers to the patterns of inheritance that follow the basic laws established by Gregor Mendel, including the segregation of alleles and independent assortment. In the context of flower color, these laws are used to explain how alleles governing pigment production are passed from parents to offspring, and how these alleles segregate into distinct phenotypes in the F1 and F2 generations.

Dominance Relationships

Dominance explains how certain alleles may mask the expression of others in a heterozygote. In flower color inheritance, one allele (for instance, red) may completely dominate over others (such as orange or yellow), leading to particular phenotypes in the hybrid and segregating generations. Understanding which alleles are dominant or recessive is key for predicting the outcomes of crosses.

Epistasis

Epistasis is the phenomenon where the expression of one gene is affected by one or more other genes. In the inheritance of flower color, the interaction between two different gene loci can modify the expected Mendelian ratios, such as resulting in a 9:3:4 ratio in the F2 generation. This indicates that one gene may mask or modify the expression of another, leading to a variety of possible phenotypes depending on the combination of alleles present.

Transcript

00:01 In snapdragons, the researchers should do some control tests before they move on.

00:07 And so i can propose too.

00:09 So the first control that they could do is take each strain or each plant.

00:17 And then they grind up those flower petals separately.

00:30 Sort of like, here's one test tube, which is plant one, and then here's the other test tube.

00:38 And of course you would use replicates and all of that good stuff.

00:41 And then you would ask if there's a color change.

00:44 And of course, because of, you know, the separate nature of how these plants were ground, they should remain colorless because they're not together.

00:55 The other control that could be done is a simple breeding to take each plant strain, so plant one and cross that with plant two.

01:06 And then the offspring from that breeding should be purple.

01:12 Because i think what's happening is that you're looking at the gene products of two different genes that are working together to make a reddish purple color.

01:22 And so if you've read those two, if it was a simple, you know, complete inheritance pattern, you should get purple, reddish purple plants or flowers in the f1.

01:32 And so that leads us to be part.

01:35 The most likely explanation is that this phenomenon, the red purple pigment, is that.

01:41 Created by the action of two genes and those genes are working in a color pathway to make purple reddish purple and so when you take petals from plant one and plant two and grind them together you get complementation to happen and so the action of one gene product complements the action of the other so even if one plant has a defective gene when they're combined the other plant's functional gene makes it turn to a purple color.

02:21 So they're complements...

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