question_answer

Directions : (16 - 20)

Read the passage given below and answer the following questions.

Mendel's mainly described those traits that have distinct alternate forms such as flower colour which are either purple or white. But if you look around, you will find that there are many traits which are not so distinct in their occurrence and are spread across a gradient. 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. F. Galton in 1883 suggested that many instances of continuous variation are heritable. He was impressed by the fact that taller humans beings generally produce taller children. He suggested that characters such as height and mental capabilities in humans are heritable although these show a continuous range of variation in a population. Gallon's postulate gained experimental support when it was found that at least in, some instances the same character can be determined by more than one gene, each with the same but cumulative or additive phenotypic effect. Quantitative characters like plant height, yield of crops (size, shape and number of seeds and fruits per plant), intelligence in human beings and milk yield in animals have been found to be determined by many genes and their effects have been found to be cumulative. Each gene has a certain amount of effect, and the more the number of dominant genes, the greater expression of the character. Though polygenic traits can be easily influenced by environment, these are generally controlled by three or more genes with phenotype reflecting the contribution of each allele.

Polygenic traits are controlled by how many gene(s)?

A) One gene

B) Two genes

C) Three or more genes

D) Not controlled by gene