Chapter 23 - The Evolution of Populations Flashcards
The three main mechanisms that can cause changes in allele frequencies:
natural selection, genetic drift, and gene flow
Microevolution -
evolution on its smallest scale, shown in changes in allele frequencies in a population over generations
Genetic drift -
chance events that alter allele frequencies
Gene flow -
the transfer of alleles between populations
Natural selection/adaptation -
consistently improves the degree to which organisms are well suited for life in their environment
Genetic variation -
differences among individuals in the composition of their genes or other DNA sequences
Gene variability -
genetic variation at the whole-gene level can be quantified as the average percentage of loci that are heterozygous
Nucleotide variability -
genetic variation can be measured at the molecular level of DNA
Phenotype -
the product of an inherited genotype and many environmental influences
Genetic variation originates from
mutation, gene duplication, or other processes that produce new alleles and new genes
Mutation -
a change in the nucleotide sequence of an organism’s DNA
“heterozygote protection” -
recessive genes that can maintain a pool of alleles that may be harmful under present conditions, but that could be beneficial if the environment changes
Neutral variation -
differences in DNA sequence that do not confer a selective advantage or disadvantage
Sexual reproduction then shuffles existing alleles and deals them at random to produce individual genotypes.
Three mechanisms contribute to this shuffling:
crossing over, independent assortment of chromosomes, and fertilization
A population -
a group of individuals of the same species that live in the same area and interbreed, producing fertile offspring
The characterized genetic makeup of a population -
gene pool, consisting of all copies of every type of allele at every locus in all members of the population
“fixed in the gene pool”
If only one allele exists for a particular locus in a population, that allele is said to be _________ and all individuals are homozygous for that allele.
Hardy-Weinberg equilibrium -
a population that is not evolving (allele and genotype frequencies will remain constant from generation to generation) is said to be in
Condition 1 for Hardy-Weinberg equilibrium -
No mutations
Consequence if Condition Does Not Hold: The gene pool is modified if mutations occur or if entire genes are deleted or duplicated.