The Hardy-Weinberg theorem describes the gene pool of a nonevolving population.This theorem states that the frequencies of alleles and genotypes in a population’s gene pool will remain constant over generations unless acted upon by agents other than Mendelian segregation and recombination of alleles. The shuffling of alleles by meiosis and random fertilization has no effect on the overall gene pool of a population. A population must satisfy five conditions if it is to remain in Hardy-Weinberg equilibrium:Extremely large population size. In small populations, chance fluctuations in the gene pool can cause genotype frequencies to change over time. These random changes are called genetic drift.No gene flow. Gene flow, the transfer of alleles due to the migration of individuals or gametes between populations, can change the proportions of alleles.No mutations. Introduction, loss, or modification of genes will alter the gene pool.Random mating. If individuals pick mates with certain genotypes, or if inbreeding is common, the mixing of gametes will not be random.No natural selection. Differential survival or reproductive success among genotypes will alter their frequencies.
2. What are the three major factors that alter allele frequencies in a population?
Natural selection, genetic drift ( founder effect and bottleneck effect) and the gene flow.(immigration/emigration)
3. How is genetic variation preserved in a population?
The tendency for natural selection to reduce variation is countered by mechanisms that preserve or restore variation, including diploidy and balanced polymorphisms.Diploidy in eukaryotes prevents the elimination of recessive alleles via selection because recessive alleles do not affect the phenotype in heterozygotes.Even recessive alleles that are unfavorable can persist in a population through their propagation by heterozygous individuals.Heterozygote protection maintains a huge pool of alleles that may not be suitable under the present conditions but may become beneficial when the environment changes.
5 facts on this chapter:
. Chromosomal mutations delete, disrupt, duplicate, or rearrange many loci at once.
. Gene pool is all of the alleles at all loci in all the members of a population. in diploid species each individual has two alleles for a particular gene, the individual may be either homozygous or hetero.
. if all members of a pop are homozygous for the same allele, the allele is said to be fixed.
. relative fitness refers to the contribution an organism makes to the gene pool of the next generation relative to the contribution of other members.
. Mutations can alter gene frequency but are rare.
Natural selection cannot produce perfect organisms because selection can only edit existing variations. evolution is limited by historical constraints, adaptations are often compromises, and chance, natural selection, and the environmental interact. there are 3 different types of selections:directional, disruptive, and stabilizing selections.
A long video about mutations, genetic drift, and gene flow:
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