Race and Genetics - Genetic Variation

Genetic Variation

Genetic variation comes from mutations in genetic material, migration between populations (gene flow), and the reshuffling of genes through sexual reproduction. The two main mechanisms that produce evolution are natural selection and genetic drift. A special case of genetic drift is the founder effect. Epigenetic inheritance are heritable changes in phenotype (appearance) or gene expression caused by mechanisms other than changes in the underlying DNA sequence.

Many human phenotypes are polygenic, meaning that they depend on the interaction among many genes. Polygeneity makes the study of individual phenotypic differences more difficult. Additionally, phenotypes may be influenced by environment as well as by genetics. The measure of the genetic role in phenotypes is heritability.

Nucleotide diversity is based on single mutations called single nucleotide polymorphisms (SNPs). The nucleotide diversity between humans is about 0.1%, which is 1 difference per 1,000 nucleotides between two humans chosen at random. This amounts to approximately 3 million SNPs since the human genome has about 3 billion nucleotides. It is estimated that a total of 10 million SNPs exist in the human population.

Recent analysis has shown that non-SNP variation accounts for much more human genetic variation than single nucleotide diversity. This non-SNP variation includes copy number variation and results from deletions, inversions, insertions and duplications. It is estimated that approximately 0.4% of the genomes of unrelated people typically differ with respect to copy number. When copy number variation is included, human to human genetic variation is estimated to be at least 0.5%.