Neo-Darwinism (the modern synthesis) combines Darwin's theory of natural selection with Mendelian genetics. It explains natural selection in terms of genes and alleles, which Darwin did not know about.Sources of genetic variation:
• mutation creates new alleles
• meiosis produces new combinations of alleles by crossing over and independent assortment
• random fertilisation combines alleles from two parents.All the alleles of all the genes in a population make up its gene pool. The proportion of one allele in the gene pool is its allele frequency.The neo-Darwinian explanation:
1. Individuals in a population vary because they have different alleles.
2. An environmental factor, a selection pressure such as predation, disease or competition, affects survival.
3. Individuals with advantageous alleles are more likely to survive, reproduce and pass on their alleles.
4. Over many generations, the frequency of the advantageous allele in the gene pool increases, while disadvantageous alleles become less common.Evolution is therefore defined as a change in allele frequency in a population over time.Worked example: a population of moths is exposed to a new predator that sees pale moths more easily. The frequency of the allele for dark colour rises from 0.2 to 0.6 over 30 generations. The allele frequency has increased by 0.4, a factor of 3, so the population has evolved.
• mutation creates new alleles
• meiosis produces new combinations of alleles by crossing over and independent assortment
• random fertilisation combines alleles from two parents.All the alleles of all the genes in a population make up its gene pool. The proportion of one allele in the gene pool is its allele frequency.The neo-Darwinian explanation:
1. Individuals in a population vary because they have different alleles.
2. An environmental factor, a selection pressure such as predation, disease or competition, affects survival.
3. Individuals with advantageous alleles are more likely to survive, reproduce and pass on their alleles.
4. Over many generations, the frequency of the advantageous allele in the gene pool increases, while disadvantageous alleles become less common.Evolution is therefore defined as a change in allele frequency in a population over time.Worked example: a population of moths is exposed to a new predator that sees pale moths more easily. The frequency of the allele for dark colour rises from 0.2 to 0.6 over 30 generations. The allele frequency has increased by 0.4, a factor of 3, so the population has evolved.