Match List I with List II

Choose the correct answer from the options given below:

A-III, B-IV, C-I, D-II

The correct answer is Option (4) → A-III, B-IV, C-I, D-II

A. When a single gene can exhibit multiple phenotypic expression such a gene is called a pleiotropic gene. The underlying mechanism of pleiotropy in most cases is the effect of a gene on metabolic pathways which contribute towards different phenotypes. An example of this is the disease phenylketonuria, which occurs in humans. The disease is caused by mutation in the gene that codes for the enzyme phenyl alanine hydroxylase (single gene mutation). This manifests itself through phenotypic expression characterised by mental retardation and a reduction in hair and skin pigmentation.

B. Haemophilia is a sex linked recessive disease, which shows its transmission from unaffected carrier female to some of the male progeny has been widely studied. In this disease, a single protein that is a part of the cascade of proteins involved in the clotting of blood is affected. Due to this, in an affected individual a simple cut will result in non-stop bleeding.

C. The inheritance of flower colour in the dog flower (snapdragon or Antirrhinum sp.) is a good example to understand incomplete dominance. In a cross between true-breeding red-flowered (RR) and true- breeding white-flowered plants (rr), the F1 (Rr) was pink.

D. Mendel’s Law of Independent Assortment states that ‘when two pairs of traits are combined in a hybrid, segregation of one pair of characters is independent of the other pair of characters’. This law is illustrated by a 9:3:3:1 phenotypic ratio, which is observed in a dihybrid cross (a cross involving two different traits). For example, when crossing plants with different seed shapes and colors, this ratio indicates the different combinations of these traits in the offspring.