What is the difference between pure culture and contamination?

In simple words, a particular bacterial culture that is contaminated indicates the presence of other types of bacteria in that culture. In contrast, mixed culture indicates a culture or medium where two or more than two types of bacteria with different strains and species are present.

Answer- Random forces lead to genetic drift

Explanation- These changes in relative allele frequency, called genetic drift, can either increase or decrease by chance over time. Both possibilities decrease the genetic diversity of a population. Genetic drift is common after a population experiences a population bottleneck.

I hope that this helps you understand. I hope that you and your family are well during this pandemic. You have my prayers. So please stay home and stay safe. With all of that said, I have you have a wonderful day!