Chapter 6, Problem 1PDT

Summary Introduction

To estimate: The expected response to selection in the next generation in a study of selection on the leg length of migratory locusts, where the mean leg length is 18.6 mm, the selection gradient is = -0.13/mm, the phenotypic variance is P = 1.4 mm2, and the heritability is h² = 0.37.

Introduction: In a diploid cell chromosomes are present in pairs. Chromosomes are transferred from the parent to the offspring. A chromosome is a part of a human genome. It is made up of two arms, one arm is the short arm and the other arm is the long arm. Genes are present on the chromosome. The combination of the genotypic variance and environmental factors refers to the phenotypic variance.

Explanation of Solution

Migratory locusts are large insects. Environmental factors along with the genotypic factors cause phenotypic variance.

$\begin{array}{c}\text{Mean leg length = 18}\text{.6 mm}\\ \text{Selection gradient }\left(\text{β}\right)\text{ = }-\text{0}\text{.13 / mm}\\ \text{Phenotypic variance }\left(\text{P}\right)\text{ = 1}{\text{.4 mm}}^{\text{2}}\\ {\text{h}}^{\text{2 }}\text{=0}\text{.37}\end{array}$

According to Breeders formula:

${\text{R=h}}^{\text{2}}\text{×β}$

R refers to the response to selection

$\begin{array}{l}\text{R=0}\text{.37×}-\text{0}\text{.13}\\ \text{R=}-\text{0}\text{.0481}\end{array}$

The expected response to selection will be -0.0481.

Summary Introduction

To predict: The average leg length in the next generation.

Introduction: In a diploid cell chromosomes are present in pairs. Chromosomes are transferred from the parent to the offspring. A chromosome is a part of a human genome. It is made up of two arms, one arm is the short arm and the other arm is the long arm. Genes are present on the chromosome. The combination of the genotypic variance and environmental factors refers to the phenotypic variance.

Explanation of Solution

Factors responsible for the phenotypic variance maybe the genotypic factors along with several environmental factors due to which the phenotypic variance occurs. The relation between the selection factor and the heritability is given by the Breeders formula. To find out the response to selection heritability is multiplied with the selection gradient;

Therefore, the average leg length for the next generation can be predicted with the help of the Breeders formula.

The given information is as follows:

$\begin{array}{c}\text{Mean leg length = 18}\text{.551 mm}\\ \text{Selection gradient }\left(\text{β}\right)\text{ = }-\text{0}\text{.13 / mm}\\ \text{Phenotypic variance }\left(\text{P}\right)\text{ = 1}{\text{.4 mm}}^{\text{2}}\\ {\text{h}}^{\text{2 }}\text{=0}\text{.37}\end{array}$

According to Breeders formula:

${\text{R=h}}^{\text{2}}\text{×β}$

R refers to the response to selection

$\begin{array}{l}\text{R=0}\text{.37×}-\text{0}\text{.13}\\ \text{R=}-\text{0}\text{.0481}\end{array}$

After adding the response to selection which is -0.0481 as calculated above with the mean leg length which is 18.6 mm as given in the question, the average leg length in the next generation will be as follows:

$\begin{array}{l}=\text{18}\text{.6}+\left(-\text{0}\text{.0481}\right)\\ =18.551\end{array}$

Therefore, the average length in the next generation will be 18.551.