Chapter 3, Problem 2P

In four-o’clocks, the allele for red flowers is incompletely dominant to the allele for white flowers, so heterozygotes have pink flowers. What ratios of flower colors would you expect among the offspring of the following crosses: (a) pink × pink,(b) white × pink, (c) red × red, (d) red × pink,(e) white × white, and (f) red × white? If you specifically wanted to produce pink flowers, which of these crosses would be most efficient?

Summary Introduction

To determine:

The ratio of flower colors that would be expected among the offspring of the crosses pink × pink, white × pink, red × red, red × pink, white × white, and red × white.

Introduction:

According to Mendel's conclusion, a pair of factors control the expression of a trait (a term that was used by Mendel for genes), and each factor of the pair segregate from each other during gamete formation.

Explanation of Solution

In four-o’ clocks, alleles of the red flowers are incompletely dominant to the allele for white flowers. Consider that genotype of red flowers is AA, then genotype of white flowers would be aa. Pink flowers are producing from the cross of these two flowers so its genotype would be Aa.

Condition (a)

The cross of two pink flowers (Aa×Aa) is taking place means the formed gametes would be A and a from both the parents. The ratio of the flowers that are expected to produce among the offspring of this cross is shown in the Punnett square.

♀/♂	A	a
A	AA Red flowers	Aa Pink flower
a	Aa Pink flower	aa White flower

The obtained ratio of red flowers, pink flowers, and white flowers is 1:2:1.

Condition (b)

The cross of white and pink flower (Aa×aa) is taking place means one parent will produce two different types of gametes that is A and a, and another parent will produce only one type of gamete that is a. The ratio of the flowers that are expected to produce among the offspring of this cross is shown in the Punnett square.

♀/♂	A	a
a	Aa Pink flower	aa White flower
a	Aa Pink flower	aa White flower

The obtained ratio of pink flowers and white flowers is 1:1.

Condition (c)

The cross of two red flowers (AA×AA) is taking place means parents will produce only dominant gametes. The ratio of the flowers that is expected to produce among the offspring of this cross is shown in the Punnett square.

♀/♂	A	A
A	AA Red flower	AA Red flower
A	AA Red flower	AA Red flower

All offspring that would be produced from this cross would be red flowers because both the parents are homozygous dominant.

Condition (d)

The cross of red and pink flower (AA×Aa) is taking place means one parent will produce two different types of gametes that is A and a, and another parent will produce only one type of gamete that is A. The ratio of the flowers that is expected to produce among the offspring of this cross is shown in the Punnett square.

♀/♂	A	A
A	AA Red flower	AA Red flower
a	Aa Pink flower	Aa Pink flower

The obtained ratio of pink flowers and red flowers is 1:1.

Condition (e)

The cross of two white flowers (aa×aa) is taking place means parents will produce only recessive gametes. The ratio of the flowers that is expected to produce among the offspring of this cross is shown in the Punnett square.

♀/♂	a	a
a	aa White flower	aa White flower
a	aa White flower	aa White flower

The offspring that would be produced from this cross would be white flowers because both the parents are homozygous recessive.

Condition (f)

The cross of red flowers and white flowers (AA×aa) is taking place means one parent is homozygous dominant so it would produce only dominant gamete that is A. Another parent is homozygous recessive so it will produce only recessive alleles that is a. The ratio of the flowers that is expected to produce among the offsprings of this cross is shown in the Punnett square.

♀/♂	A	A
a	Aa Pink flower	Aa Pink flower
a	Aa Pink flower	Aa Pink flower

All flowers will be of pink color because allele of red flower is incompletely dominant over the allele of white flower.

Summary Introduction

To determine:

The cross that would be most efficient to produce pink flowers.

Introduction:

Inheritance is a mechanism in which traits of the parents transfer into the offsprings of the next generation. Gregor Mendel was a monk, and he discovered three laws that describe the inheritance of factors from parents to offsprings.

Explanation of Solution

The cross of red and white flowers would be more efficient to produce pink flowers. Red flowers are homozygous dominant means the genotype of these flowers would be AA, and white flowers are homozygous recessive, which means its both gametes are recessive means aa. The cross of red flower and white flowers is as follows:

♀/♂	A	A
a	Aa Pink flower	Aa Pink flower
a	Aa Pink flower	Aa Pink flower

It can be observed from the cross that all the produced offsprings are pink in color. Therefore, the cross of red flower and white flower would be efficient to produce pink flowers.