Concept 13.4: Genetic variation produced in sexual life cycles contributes to evolution

Flashcards from Concept 13.4 of Pearson's Campbell Biology, Twelfth Edition.

Mutations

Changes in an organism’s DNA that are the original source of genetic diversity

• Creates different versions of genes called alleles

Alleles

Different versions of genes created by mutations

• Reshuffling these during sexual reproduction produces genetic variation

Chromosomal behavior

What is responsible for most of the variation that arises in each generation during meiosis and fertilization, including:

• Independent assortment of chromosomes

• Crossing over

• Random fertilization

Independent assortment

The sorting of maternal and paternal homologs into daughter cells independently of the other pairs with random orientations

n

The haploid number

• 2 to the power of this represents the number of combinations possible when they assort independently into gametes

• This is 23 in humans, leading to 2²³ (over 8 million) possible combinations

Recombinant chromosomes

Chromosomes that combine DNA inherited from each parent during crossing over, allowing for variation within a single chromosome

• 1 to 3 crossover events occur per chromosome in humans

Random fertilization

The fact that any sperm can fuse with any ovum (unfertilized egg)

• The fusion of two gametes (8.4 million possible combinations) produces a zygote with any of about 70 trillion diploid combinations, adding a unique genetic identity

Genetic variation

Created through natural selection, mutations, and meiosis

• Asexually reproducing organisms increase this by incorporating foreign DNA from the environment