Microevolution II Flashcards
Microevolutionary studies
examine how processes such as mutation, natural selection, recombination, migration, non-random mating, and genetic drift determine as well as change the genetic composition of populations
5 assumptions of HWE
- There is no mutation
- The population is infinitely large
- Mating among individuals is random
- Individuals are not moved into or out of population
- All individuals have equal probabilities of survival and of reproduction
What 2 processes produce the variation in gene pools that contribute to differences in individuals?
mutation and sexual recombination
Synonymous mutations
mutations that don’t change the encoded amino acid
Non-synonymous mutations
changes in nucleotides that change amino acids
Factors that vary rates of mutation
- sex
- generation time
- environment
- stress
2 principal ways to not have random mating
- Assortative mating
- Inbreeding
Assortative mating
like genotypes mate w/ each other or avoid each other
Inbreeding
mating among individuals that are more closely related than those drawn by chance from the population
Positive assortative mating
-decreases heterozygosity for the gene affecting the trait
-heterozygotes are decreased by half each generation w/ complete positive assortative mating
Negative assortative mating
-increases heterozygosity for the gene(s) affecting that trait
Effect of inbreeding
-changes genotype frequencies by increasing the proportion of homozygotes and reduces the proportion of heterozygotes across the entire genome
-most extreme case (selfing): has effects just like positive assortative mating but across the WHOLE genome
Evolutionary consequences of non-random mating
- The genotype changes caused by assortative mating affect only the loci contributing to the phenotype
- The genotype changes caused by inbreeding affect all loci in the genome
- Inbreeding results in genome-wide loss of heterozygosity (loss of diversity)
- Inbreeding and assortative mating only affect genotype frequencies so their effects may be quite ephemeral or temporary
- Inbreeding reduces fitness by generating offspring homozygous for deleterious alleles (inbreeding depression)
Self-fertilizing species typically exhibit _______ levels of diversity
lower
Inbreeding depression
Inbreeding reduces fitness through the generation of offspring homozygous for deleterious alleles
Genetic drift
-basic mechanism of evolution
-evolutionary equivalent of a sampling error
-definition: variation in the relative frequency of different genotypes in a small population, owing to the chance disappearance of particular genes as individuals die or do not reproduce
Long-term patterns of genetic drift
- population bottleneck
- founder effect
Population bottleneck
when a population goes through a period of unusually small population size
-greatly reduces genetic variation
-many genes may be lost
Founder effect
when a population does through this period of unusually small population size at a time when it arrives to a new, uncolonized area
-may have a non-random sample of the genes present in the original population and/or reduced genetic variation from the original population
-Ex: Canadian Mennonites
5 effects of genetic drift
- Genetic drift is significant in small populations
- Genetic drift can cause allele frequencies to change at random
- Genetic drift can lead to loss of genetic variation within populations
- Genetic drift can lead to differentiation among populations
- Genetic drift can cause harmful alleles to become fixed
Gene flow
the transfer of alleles into or out of a population due to the movement of fertile individuals or their gametes
-can also change allele frequencies
