B4. Natural Selection

Question 1

The process of natural selection

What does it begin with?

What happens afer?

Then what happens?

Here’s how it works: (5 steps)

What is evolution?

Answer 1

Randomly-occurring mutations sometimes result in a new allele being formed. This can be harmful, which usually means that the mutated allele quickly dies out.

However, some mutations can produce alleles that are beneficial to an organism (e.g. a protein is produced that works better than the original), helping the organism to survive in certain environments.

When the allele codes for a characteristic that increases the chances of an organism surviving, its frequency within the population can increase. This process is known as natural selection. Here’s how it works:

1. There’s differential reproductive success in a population- individuals that have an allele that increases their chance of survival are more likely to survive, reproduce and pass on their genes (including the beneficial allele), than individuals with less advantageous alleles.
2. This means that a greater proportion of the next generation inherits the beneficial allele.
3. They, in turn, are more likely to survive, reproduce and pass on their genes.
4. So the frequency of the beneficial allele in the population increases from generation to generation.
5. Over generations this leads to evolution as the advantageous alleles become more common in the population.

Evolution is the gradual change in species over time. It has led to the huge diversity of living organisms on Earth. Adaptation and selection are both key factors in evolution.

Question 2

Types of adaptations
Natural selection leads to organisms becoming better adapted to their environment. Adaptations are features that help organisms to survive in their environment. They can be …(include definitions)

Answer 2

1. Behavioural adaptations
   These are ways an organism acts that increase its chance of survival.
2. Physiological adaptations
   These are processes inside an organism’s body that increase its chance of survival.
3. Anatomical (structural) adaptations
   These are structural features of an organism’s body that increase its chance of survival.

Question 3

Tip: Organisms that are well adapted to their environment have a ___________ ____________over less-well adapted organisms.

Answer 3

Tip: Organisms that are well adapted to their environment have a selective advantage over less-well adapted organisms.