Question

In morning glory flowers, plants with red flowers can be homozygous RR or heterozygous Rr. Plants that are rr have white flowers. How can you determine the genotype of a plant that has red flowers?

Multiple Choice

A. Cross the red plant with another red plant, and then cross the F₁ population with each other to see if any white plants appear.

B. The phenotype reflects the genotype, so the plant must be homozygous for the trait.

C. Cross the red plant with a white plant to see how many red plants appear.

D. Cross the red plant with a white plant to see if any white plants appear.

E. Cross the red plant with another red plant to see if any white plants appear.

Answer 1

ANSWER :-

• Basically, the preference would be a test cross. But, for carrying out a test cross, there would be two different phenotypic ratios observed which reflects the different genotypes.
• Lets consider a cross between a red plant and a white plant which is homozygous recessive and presence of all red plants (character) would indicate presence of homozygous dominant individual.

	R	R
r	Rr	Rr
r	Rr	Rr

All the four individuals are red plants and will be heterozygous.

• A test cross would indicate presence of Heterozygous individuals if the phenotypic ratio obtained is 1:1 with respect to the red plant to the white plant.

	R	r
r	Rr	rr
r	Rr	rr

Two individuals will be heterozygous offsprings with a red plant phenotype and two offsprings will be homozygous recessive with white plant phenotype indicating a ratio of 1:1.

So, the most appropriate answer would be option 'C' and 'D' would be the most appropriate answers. Others options does not indicate a test cross with a homozygous recessive parent and hence would not be indicative of identification of genotype.

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