Unit B

Module 4 ~ Lesson 1

Selective Advantages

nick goodrum from Catfield in Norfolk, United Kingdom / CC BY (https://creativecommons.org/licenses/by/2.0)

The peppered moth (Biston betularia) has two colour variations in its population – light and dark. Before 1848, the dark variation was very rare. In the middle of the eighteenth century, the Industrial Revolution started to change the peppered moths' environment. The soot released from industries covered trees and darkened the forest environment. After the Industrial Revolution, 90% of the peppered moths were of the dark colour variation. What caused this change in colour variations?

Mutations can provide variation within a population. Mutations are changes in the genetic material (DNA) of an organism. Mutations are naturally occurring at a steady rate in populations. This rate can be increased if mutagens such as UV radiation or certain chemical compounds are introduced into the environment

Some mutations are harmless and have no effect. Others may create a new variation that provides a selective advantage and increases the offspring's chances of survival or a selective disadvantage and reduces the offspring's chances of survival.

Parent fruit flies were bombarded with X-rays. The parents then mated with healthy fruit flies, and the offspring had many mutations. The following image shows examples of some of these mutations.

The wingless mutation will cause a disadvantage to the fly, and the offspring likely will not survive to reproduce. Since the offspring doesn't reproduce, it will not pass on the disadvantageous mutation.