Chapter 5, Problem 32P

In experiments published in $\text{1918}$ that sought to verifyand expand the genetic linkage and recombination theoryproposed by Morgan, Thomas Bregger studied potential

genetic linkage in corn (Zea mays) for genes controllingkernel color (colored is dominant to colorless) and starchcontent (starchy is dominant to waxy). Bregger performed two crosses. In Cross $\text{1}$, $\text{pure-breeding}$ colored, starchykernel plants ( $\text{C1 Wx/C1 Wx}$) were crossed to plants purebreeding for colorless, waxy kernels ( $\text{c1 wx/c1 wx}$). The $\text{F1}$ of this cross were $\text{test-crossed}$ to colorless, waxy plants.The $\text{test-cross}$ progeny are as follows:

$\begin{array}{cc}\text{<x-custom-btb-me data-me-id="2523" class="microExplainerHighlight">Phenotype</x-custom-btb-me>}& \text{Number}\\ \text{Colored, waxy}& \text{310}\\ \text{Colored, starchy}& \text{858}\\ \text{Colorless, waxy}& \text{781}\\ \text{Colorless, starchy}& \text{311}\\ & \text{2260}\end{array}$

In Cross $\text{2}$, plants $\text{pure-breeding}$ for colored, waxy kernels( $\text{C1 wx/C1 wx}$) and colorless, starchy kernels ( $\text{c1 Wx/c1 Wx}$)were mated, and their $\text{F1}$ were $\text{test-crossed}$ to colorless, waxy plants. The $\text{test-cross}$ progeny are as follows:

$\begin{array}{cc}\text{Phenotype}& \text{Number}\\ \text{Colored, waxy}& \text{340}\\ \text{Colored, starchy}& \text{115}\\ \text{Colorless, waxy}& \text{92}\\ \text{Colorless, starchy}& \text{298}\\ & \text{845}\end{array}$

a. For each set of $\text{test-cross}$ progeny, determine whethergenetic linkage or independent assortment is morestrongly supported by the data. Explain the rationale for your answer.

b. Calculate the recombination frequency for each of theprogeny groups.

c. Are the results of these two experiments mutually compatible with the hypothesis of genetic linkage? Explainwhy or why not.

d. Merge the two sets of progeny data and determine thecombined recombination frequency.