D4.1.2 Roles of mutation and sexual reproduction Notes

Variation Is Essential for Natural Selection

1. Darwin's theory of evolution hinges on variation within populations.
2. Without variation, there would be no differences for selection to act upon.
3. Darwin observed that populations exhibit variation in traits such as height, skin color, and blood group in humans.
4. In other species, variation may not be immediately obvious, but careful observation always reveals it.

Mutation Creates New Alleles, Expanding the Gene Pool

1. Mutation is the original source of variation.
2. How Mutation Works:
   1. Mutations occur as changes in DNA sequences, creating new alleles.
   2. These new alleles enlarge the gene pool of a population.

Meiosis Generates New Combinations of Alleles

1. Meiosis increases genetic diversity by shuffling existing alleles.
2. How Meiosis Works:
   1. Crossing Over: Homologous chromosomes exchange genetic material, producing new allele combinations.
   2. Independent Assortment: The random orientation of bivalents ensures that each gamete has a unique combination of alleles.
3. This means every cell produced by meiosis in an individual is likely to carry a different combination of alleles.

Sexual Reproduction Combines Alleles from Two Parents

1. Sexual reproduction brings together genetic material from two individuals, further increasing variation.
2. How It Works:
   1. Male and female gametes, typically from different parents, fuse to form a zygote.
   2. This process combines alleles from two individuals, allowing beneficial mutations to come together.
3. Offspring therefore have unique combinations of alleles that may differ significantly from either parent.