Chapter 10, Problem 16A

Summary Introduction

Introduction:

A cross that involves hybrids for a single trait is called a monohybrid 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. Some traits are dominant while some are recessive.

Answer to Problem 16A

Correct answer :

The correct answer is option C. It is a recessive trait

Explanation of Solution

Explanation/justification for the correct answer:

Option C. It is a recessive trait− Let us consider the allele for curled ears are C and c.

A CC cat will produce two gametes- male and female- each with C allele. A cccat will produce two types of gametes- male and female- each with c allele. If a non-curled cat ( CC ) is crossed with a curled cat ( cc ), there is only one possible genotype; Cc . Since the resulting phenotypesare cats with non-curled ears, it is clear that the curled ear is a recessive trait which is visible only when it is present in homozygous condition.

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

	C	C
c	Cc	Cc
c	Cc	Cc

Now if cats with non-curled ears of genotype ( Cc ) is crossed with another cat with non-curled ears of genotype ( Cc ), the resultant genotypes will be CC, Cc, cc in the ratio of 1:2:1. The phenotypic ratio will be 3:1 non-curled to curled ears.

	C	c
C	CC	Cc
c	Cc	cc

Hence this is the correct option.

Explanation for incorrect answer:

Option A. Curled ears are a result of crossing over- No curled ears are not a result of crossing over. Hence this is not the correct option.

Option B. It is a dominant trait- If curled ears were a dominant trait, it would be visible in the first crossing when cat with curled ears was crossed with cat with non-curled ears. A single allele is needed for dominant trait to be visible. Hence this is not the correct option.

Option D. More crosses need to be done to determine how the trait is inherited-Two crosses are enough to determine the nature of trait. All the possible genotypes and phenotypes are produced in two crossings.

Hence this is not the correct option.