Hereditary and Variation MCQs for NEET — Botany Questions with Answers

Mendel's studies mainly described those traits that have distinct alternate forms such as flower colour which are either purple or white. Human skin color, however, is an example of polygenic inheritance, which is not distinct and is spread across a gradient, unlike the traits Mendel studied.

According to the NCERT text, 'Such traits are generally controlled by three or more genes and are thus called as polygenic traits. Besides the involvement of multiple genes, polygenic inheritance also takes into account the influence of environment. ... In a polygenic trait the phenotype reflects the contribution of each allele, i.e., the effect of each allele is additive.'

The NCERT text states: 'The genotype with all the dominant alleles (AABBCC) will have the darkest skin colour and that with all the recessive alleles (aabbcc) will have the lightest skin colour.'

The NCERT text defines this: 'There are however instances where a single gene can exhibit multiple phenotypic expression. Such a gene is called a pleiotropic gene.'

The NCERT text explains: 'The underlying mechanism of pleiotropy in most cases is the effect of a gene on metabolic pathways which contribute towards different phenotypes.'

The text states: 'For example, in humans we don’t just have tall or short people as two distinct alternatives but a whole range of possible heights. Such traits are generally controlled by three or more genes and are thus called as polygenic traits.'

The NCERT text says: 'As expected the genotype with three dominant alleles and three recessive alleles would have an intermediate skin colour.' An individual with three dominant alleles (e.g., AaBbCc) would have an intermediate phenotype.

The NCERT text explicitly mentions: 'An example of this is the disease phenylketonuria, which occurs in' (the sentence is cut off, but it's clearly stated as an example of pleiotropy).

The NCERT text states: 'In a polygenic trait the phenotype reflects the contribution of each allele, i.e., the effect of each allele is additive.'

Mendel's traits were distinct, like 'flower colour which are either purple or white.' Human skin color is presented as an example of a trait that is 'not so distinct in their occurrence and are spread across a gradient,' which is characteristic of polygenic inheritance, not Mendelian distinct traits.