In silkmoths (Bombyx mori), red eyes (re) and white-banded...

In silkmoths (Bombyx mori), red eyes (re) and white-banded wings (wb) are encoded by two mutant alleles that are recessive to those that produce wild-type traits $\left(r e^{+}\right.$ and $\left.w b^{+}\right)$; these two genes are on the same chromosome. A moth homozygous for red eyes and white-banded wings is crossed with a moth homozygous for the wild-type traits. The $\mathrm{F}_{1}$ have wild-type eyes and wild-type wings. The $\mathrm{F}_{1}$ are crossed with moths that have red eyes and white-banded wings in a testcross. The progeny of this testcross are $\begin{array}{ll}\text { wild-type eyes, wild-type wings } & 418 \\ \text { red eyes, wild-type wings } & 19 \\ \text { wild-type eyes, white-banded wings } & 16 \\ \text { red eyes, white-banded wings } & 426\end{array}$ a. What phenotypic proportions would be expected if the genes for red eyes and for white-banded wings were located on different chromosomes? b. What is the rate of recombination between the gene for red eyes and the gene for white-banded wings?

In silkmoths (Bombyx mori), red eyes (re) and white-banded wings (wb) are encoded by two mutant alleles that are recessive to those that produce wild-type traits $\left(r e^{+}\right.$ and $\left.w b^{+}\right)$; these two genes are on the same chromosome. A moth homozygous for red eyes and white-banded wings is crossed with a moth homozygous for the wild-type traits. The $\mathrm{F}_{1}$ have wild-type eyes and wild-type wings. The $\mathrm{F}_{1}$ are crossed with moths that have red eyes and white-banded wings in a testcross. The progeny of this testcross are $\begin{array}{ll}\text { wild-type eyes, wild-type wings } & 418 \\ \text { red eyes, wild-type wings } & 19 \\ \text { wild-type eyes, white-banded wings } & 16 \\ \text { red eyes, white-banded wings } & 426\end{array}$
a. What phenotypic proportions would be expected if the genes for red eyes and for white-banded wings were located on different chromosomes?
b. What is the rate of recombination between the gene for red eyes and the gene for white-banded wings?

Key Concepts

Recombination Frequency

Recombination frequency is the proportion of recombinant offspring produced in a cross and reflects the physical distance between linked genes on a chromosome. It is expressed as a percentage or in map units (centimorgans), indicating the likelihood of a crossover event occurring between two genes during meiosis.

Genetic Linkage

Genetic linkage occurs when genes are located close together on the same chromosome, causing them to be inherited together rather than assorting independently. This can lead to deviations from the expected phenotypic ratios predicted by Mendel's law of independent assortment.

Independent Assortment

Independent assortment is a fundamental principle of Mendelian genetics stating that alleles of different genes segregate into gametes independently of one another. This principle applies when genes are unlinked, or located on different chromosomes, resulting in a 1:1:1:1 phenotypic ratio in a testcross.

Testcross

A testcross is used to determine the genotype of an individual with dominant phenotypes. In a testcross, the individual is crossed with a homozygous recessive partner, allowing for the determination of whether the dominant individual is homozygous or heterozygous for the traits under study.

Transcript

0:00 Hi everyone.

00:01 My name is eric and let's go over problem 15.

00:04 So in this question, we are going over the red eyes and white banded traits found in the silk moths.

00:12 So let's go ahead and define what is given to us from the problem.

00:16 So red eyes is defined as a recessive trait.

00:22 So red eyes will be denoted as r .e.

00:26 Minus.

00:26 The same thing is with white banded minus.

00:30 So white banded wings are also a recessive trait.

00:39 And we have to understand that if we talk about the wild type traits, those are going to be considered as the re plus and the wb plus.

00:50 So these are both wild types.

00:53 Okay.

00:53 Now, wild types are going to be those dominant traits that are typically found in the species.

01:00 They're considered normal, while the re minus and the wb minus shown here are the recessive traits that are going to be considered as the non -typical unique traits.

01:15 So let's walk through the first step, which is going to be defining how they did their crosses together.

01:24 So the first cross was done with a homozygous moth for red eyes and white banded, crossing it, with a homozygous for wild type.

01:33 Okay? so they said that there's a red eyes white banded with wild type.

01:41 So red eyes is going to be red eyes minus for both.

01:48 And it's going to be white banded minus for both.

01:52 So this is the red eyes and the white banded.

01:56 So that's the first parent.

01:59 And they're crossing it with a homozygous for the wild type.

02:03 So these would both be pluses.

02:08 Okay.

02:10 And the resulting progeny will be considered the f1 generation.

02:15 The f1 generation is going to be having wild type eyes and wild type wings because we're going to be making a heterozygous progeny.