Think why did ancient human beings travelled from one place to other and how did they travelled?

During the course of evolution some organs remain in the organisms. You have studied about appendix in the digestive system. In human beings it has no role to play in the process of digestion. But in herbivores like rabbit appendix plays an important role. Such type of organs which are not useful in animal are called vestigial organs.

Sometimes vestigal organs are abruptly appears even in humanbeings. This phenomenon is called "ATAVISM". Ex : baby with tail.

There are nearly 180 vestigial organs in human beings. For example pinna, hair on skin, mammary glands in males, etc. That's why human being is said to be a moving museum of vestigial organ

Variations are quite apparent among closely related groups of organisms.

In about 1857 Gregor Johann Mendel started working on the problem of how variations were passed from one generation to other.

Mendel had choosen seven distinguishing traits: flower colour, position, seed colour, shape, pod colour, pod shape, stem length.

In monohybrid experiment F1 generation express dominant trait (Eg: Yellow seeds).

In F2 generation about 75% seeds were with dominant character (Eg: Yellow seeds) and about 25% seeds were with recessive character (Eg: Green seeds). This is called phenotype and the ratio is 3:1.

In F2 generation out of 75%, 25% were pure yellow seeds 50% were yellow seeds but green as a recessive factor. Remaining 25% were pure green. This is called genotype and the ratio 1:2:1.

Every pea plant has two 'factors' which are responsible for producing a particular property or trait called allele.

The factors for each pair of characters assorts independently of the other pairs. This is known as "Law of independent assortment".

Crossing yellow and green seeds produced all yellow seeds. Because yellow is dominant factor.

Each parent passes randomly selected copy (allele) of only one of these to its offspring.

The process of acquiring characters or traits from parents is called 'Heredity'.

Each human cell contains 23 pairs of chromosomes. Out of these 22 pairs are called autosomes and one pair is called allosomes.