Variation in gene frequencies within populations can occur by chance rather than by natural selection. This is referred to as

The frequency of a mutant gene in a population is expected to increase, if the gene is

Define the following terms: $Genetic \ drift$ and $Gene \ migration$ $(Gene \ flow)$.

Given below are two statements.
Statement $I$ - According to Darwin,the gradual,inheritable variations over a long period of time lead to speciation.
Statement $II$ - According to Hugo de Vries,mutations are the cause of variations.
In the light of above statements,select the correct option given below:

When members of a population attain sexual maturity at different times preventing inter-breeding,it is termed as . . . . . . isolation.

Species that are separated by geographical barriers are called ........