Question

The gene for right-handedness is dominant over the gene for left-handedness. Most probable genotypes of two right-handed parents with the left-handed child is _______.
A. RR × rr
B. rr × Rr
C. RR × Rr
D. Rr × Rr

Answer 1

Hint: A dominant allele will express itself even in heterozygous condition. Therefore, both parents should have heterozygous genes for the trait,

Complete answer: Every gene has two alternating forms of itself. These two alternative forms of a gene are called alleles. The allele which can produce a phenotype even in the heterozygous condition is called the dominant allele, whereas the allele which can produce a phenotype only in the homozygous condition is called the recessive allele. As mentioned in the question, the offspring is left-handed. So, the phenotype of the offspring is ‘rr’, i.e., the offspring is a homozygous recessive for the given trait. Therefore, each of the parents must have one recessive allele because the offspring gets one allele each from both the parents. It means that both the parents must be a heterozygous type for the given trait because we already know that they have the dominant phenotype. So, each of the parents would have the phenotype ‘Rr’. Genes are the hereditary material that determines the trait of an organism.
Therefore, the correct answer is option D.

Additional information: There are some traits which show different behaviour than the dominant and recessive system. These differences might be seen as;
i. Incomplete dominance
ii. Codominance
iii. Multiple alleles

Note: The concept of dominant and recessive alleles was first introduced by Gregor Mendel. Both the terms aroused from Mendel’s first law, i.e. alleles that express themselves are dominant, and others that don’t, they are termed as recessive.