Question

The unit of heredity is:
a. Chromosomes
b. DNA and RNA molecules
c. Nucleus
d. Gene

Answer 1

Hint: The heredity is the passing on of traits from parents to their offspring. These traits are passed during the process of fertilization when two gametes fuse. The genetic information from parents is passed on in the form of genes that are responsible for specific traits.

Complete answer:
The gene is a sequence of nucleotides in DNA or RNA that encodes the synthesis of gene products. This gene product may be RNA or a protein. The gene is the smallest unit that can be transcribed into proteins. The gene helps to control the development and function of all organs and working systems of the body.

Genes are passed from parents to offspring. For instance, humans have 23 pairs of chromosomes i.e. 46 chromosomes in total, out of which 23 chromosomes are inherited from father and 23 are inherited from mother. The genes present on these 23 pairs are responsible for the characters of the offspring, from eye color to hair color.

We know that every cell has its nucleus which controls the working of the whole cell. The nucleus contains chromosomes which is the genetic information of the cell. A single chromosome is composed of many DNA and RNA nucleotides (nucleotides are the building blocks of DNA or RNA). These DNA or RNA molecules contain genes. As mentioned above, the genes are the small stretches of DNA or RNA that can code for any protein that controls a certain character. Therefore, when the fertilization between two gametes occurs, the nuclei of gamete cells fuse to form a zygote. The resulting zygote possesses 23 chromosomes inherited both from father and mother.
The characters of the zygote will totally depend on the genes that were inherited from its parents.

Thus, we can say that the basic unit of inheritance is genes. Genes are inherited from generation to generation in the form of chromosomes and the combination between different chromosomes also causes variability among the offspring.

Hence, The correct answer is option (D).

Note: The genetic information is stored in the nucleus of a cell. The genetic information of a cell is passed on to its generation via chromosomes. Thus, chromosomes may also be considered as a unit of heredity on a broad view. But a single chromosome may have thousands of genes that may not code for any protein thus the correct answer is gene is the basic unit of inheritance.