Chapter 10, Problem 15A

Summary Introduction

Introduction:

A cross that involves hybrids for two traits is called a dihybrid cross. Punnett developed a method to predict the possible offspring of a cross between two known genotypes. It is easier to keep a track of the possible genotypes involved in a cross.

Answer to Problem 15A

Correct answer :

The correct answer is option A.1: 1:1:1 purple tall to purple short to white tall to white short

Explanation of Solution

Explanation/justification for the correct answer:

Option A.1: 1:1:1 purple tall to purple short to white tall to white short−A purple tall plant( PpTt) will produce four types of gametes- male and female- each with either the P allele or p allele and either T or t allele. A white short plant (pptt) will produce four gametes- male and female- all with pt alleles. If a purple tall plant ( PpTt) crossed with a white short plant (pptt), there are four possible genotypes; PpTt, Pptt, ppTt and pptt . So the resulting phenotypic ratio will be 1: 1:1:1purple tall to purple short to white tall to white short.

This can be checked by drawing a Punnett square as shown below.

	PT	Pt	pT	pt
pt	PpTt	Pptt	ppTt	pptt
pt	PpTt	Pptt	ppTt	pptt
pt	PpTt	Pptt	ppTt	pptt
pt	PpTt	Pptt	ppTt	pptt

Hence this is the correct option.

Explanation for incorrect answer:

Option B. 3:2purple tall to purple short- If a purple tall plant ( PpTt) crossed with a white short plant (pptt), there are four possible genotypes; PpTt, Pptt, ppTt and pptt . So the resulting phenotypic ratio will be 1: 1:1:1 purple tall to purple short to white tall to white short.

Hence this is not the correct option.

Option C. 9:3:3:1 purple tall to purple short to white tall to white short- If a purple tall plant ( PpTt) crossed with a white short plant (pptt), there are four possible genotypes; PpTt, Pptt, ppTt and pptt . So the resulting phenotypic ratio will be 1: 1:1:1 purple tall to purple short to white tall to white short.

Hence this is not the correct option.

Option D. all purple tall-If a purple tall plant ( PpTt) crossed with a white short plant (pptt), there are four possible genotypes; PpTt, Pptt, ppTt and pptt . So the resulting phenotypic ratio will be 1: 1:1:1 purple tall to purple short to white tall to white short.

Hence this is not the correct option.