Question: If, in a plant, the red color of the flower is dominant over white. A cross was made between a plant...

Question

If, in a plant, the red color of the flower is dominant over white. A cross was made between a plant containing red flowers and another with a white flower. The cross yielded a 50% white-flowered plant and a 50% red-flowered plant. The genotype of the parent with a red flower is:
(a) Homozygous
(b) Heterozygous
(c) Cannot be determined
(d) Can be homozygous and heterozygous

Answer 1

Solution

In the Mendel hybridization experiment the genotypic ratio obtains after ${ F }_{2}$ generation is 1:2:1 which means one-fourth part is homozygous dominant, two-part is heterozygous dominant, and remain one-fourth part is homozygous recessive.

Complete answer:
The red color flower is the dominant character expressed with (RR) and the white color flower is a recessive character expressed with (rr). When the cross takes place between both the plant
RR X rr

${ F }_{1}$ generation gives a heterozygous plant with a flower having genotype Rr.
In ${ F }_{2}$ generation the cross takes place between heterozygous plant
Rr X Rr

The phenotypic ratio obtained is 75% red flower and 25% white flower which is not similar to the given question.
To get a 50- 50 ratio of both crosses we have to use the test cross method. In a test cross, crossover takes place between ${ F }_{2}$ hybrid and recessive plants.
Rr X rr

The test cross gives 50% heterozygous red pea plant and 50% homozygous white plant. A test cross is used to determine the genotype of the dominant plant. Above cross given 50% heterozygous dominant and 50% homozygous recessive.

Additional Information: Back cross is a cross between ${ F }_{1}$ generation and one of the parents. Back cross use to get genetic similarity between parent and offspring. It is generally used in animal breeding techniques.
So, the correct answer is Heterozygous.

Note: The Mendel experiment was a success in the case of garden pea, but in some plants, it is not valid due to the formation of intermediate character is incomplete dominance. Incomplete dominance gives phenotypic and genotypic 1:2:1 which is different from the garden pea plant phenotypic ratio 3:1.