Heredity: Heredity is the transfer of genetic material from parent to offspring, from generation to another. DNA is the genetic material that is transferred across generations.
Variation: Human genetic variation is the genetic differences within and among populations. The types of variation are: a) Continuous variation b) Discontinuous variation. Some of the features of the different organisms in a species show continuous variation, and some features show discontinuous variation.
Continuous variation: Human height is an example of continuous variation. Height ranges from that of the shortest person in the world to that of the tallest person. Any height is possible between these values. So it is continuous variation. For any species a characteristic that changes gradually over a range of values shows continuous variation. Examples of such characteristics are: Height, Weight, Foot length.
Discontinuous variation: Human blood group is an example of discontinuous variation. There are only 4 types of blood group. There are no other possibilities and there are no values in between. So this is discontinuous variation. A characteristic of any species with only a limited number of possible values shows discontinuous variation. Here are some examples: Gender (male or female), Blood group (A, B, AB or O), Eye color.