7.3.1 Variation is a notable feature of the natural world

7.3.2 Mutation & recombination are the 2 sources of genetic variation

Mutation can be classified into 2 types: Somatic & germ line

Or, it can be classified into 3 types: Beneficial, Neutral and Bad

7.3.3 Evolution = Change in genetic makeup of a population over time

7.3.4 Factors

Major factors that alters allele frequencies:

Genetic drift → random

Genetic flow → random

Natural selection → not random

1. Genetic drift遗传漂变: alleles frequencies fluctuate randomly from one generation to the next 传代过程中，等位基因改变或丢失 It has a larger effect on smaller populations

   • Founder effect: 一部分个体脱离母群体，新群体与母群体的allele frequency 并不相同
   • Bottleneck effect: 大规模的死亡导致余下的个体的allele frequency与母群体不同

   It will cause a loss of genetic variation and can cause harmful alleles to be fixed(固定，不是修复)

2. Gene flow

   • Immigration迁入: 从外面来了一个别的基因型
   • Emigration迁出: 迁走一部分群体导致allele frequency改变

3. Natural Selection自然选择: 增强适应环境的alleles

   3 modes of selection:

   • Directional selection定向选择
   • Disruptive selection歧化选择
   • Stabilizing selection稳定性选择