- A Genetic variation is sometimes mistakenly thought to arise mainly from random point mutations in the germline, with migration, recombination, and drift contributing little measurable diversity to a population according to most researchers in the majority of cases studied
- B Main sources: (1) Mutation (random changes in DNA sequence); (2) Sexual recombination during meiosis (crossing over, independent assortment); (3) Gene flow (migration); (4) Genetic drift (random fluctuations); variation is the raw material for evolution by natural selection
- C Mainly crossing-over and independent assortment during meiotic recombination are sometimes mistakenly thought to be the true sources of variation, excluding much contribution from mutation, migration, or drift across generations as widely reported in standard practice
- D Genetic variation is sometimes mistakenly thought to be inherently harmful, with natural selection acting mainly to remove it, rather than serving as the raw material that natural selection itself actually requires in order to function under most conditions encountered
Correct answer: B. Main sources: (1) Mutation (random changes in DNA sequence); (2) Sexual recombination during meiosis (crossing over, independent assortment); (3) Gene flow (migration); (4) Genetic drift (random fluctuations); variation is the raw material for evolution by natural selection
Explanation: Sources of genetic variation: (1) Mutation: ultimate source of new alleles (point mutations, insertions, deletions, chromosomal rearrangements); (2) Meiotic recombination: crossing over shuffles allele combinations; (3) Independent assortment: random sorting of homologs; (4) Gene flow: immigration/emigration moves alleles between populations. Without mutation, all variation would eventually be lost.
Concept context
Origin of life, Darwin's theory, natural selection, speciation, and evidence for evolution.