30 terms

CH 21 Biology In Focus

Evolution of Populations
change in allele frequencies in a population over gen's
Impact of natural selection is only apparent in the changes in a population
Only populations evolve
Three Mech that cause allele freq to change
Natural Sel: certain traits tend to survive and reproduce at higher rates, because of those traits
Genetic drift: chance fluctuations in allele freq over generations tend to reduce gen variation. Effects of gen drift are more pronounced in small pop.
Gene flow: transfer of alleles from one population to another
evol. change above the species level (ex: origin of a new group of organisms)
product of inherited genotype and environmental influences
Source of genetic variation
new genes and alleles can arise by mutation or gene duplication
change in the nucleotide seq of a DNA
Point mutation
change in one base (ATCG) in a gene
Hard Weinberg Eq.
Used to test whether a population is evolving or not
localized group of indv capable of interbreeding and producing fertile offspring
Gene pool
consists of all copies of every type of allele at every locus in all members of the pop.
Fixed in the gene pool
that means only one allele exists for a particular locus in a population. All indv are homozygous for that allele.
Hardy Weinberg Principle
If there are no differences, we can conclude that the population is not evolving.
If population dos not meet the criteria, it can be concluded that the pop. is evolving
5 Hardy Weinberg conditions
No Mutations
Mating is random
No natural selection
Extremely large pop size
No gene flow
Natural selection, genetic drift, and gene flow can alter allele freq in a population
3 major factors alter allele freq
Natural selection
genetic drift
gene flow
Gene drift
reduce genetic variation through losses of alleles
chance events alter allele frequencies.
The founder effect
occurs when a few individuals become isolated from a larger population
Bottleneck effect
drastic reduction in population due to a sudden env. change
Effects of genetic drift
Genetic drift is significant in small populations
Genetic drift can cause allele freq to change at random
Genetic drift can lead to a loss of genetic variation within population
Genetic drift can cause harmful alleles to become fixed.
Gene flow
consists of the movement of alleles among population
Alleles can be transferred through the movement of fertile indv or gametes
Tends to reduce genetic variation among populations.
Gene Flow
can decrease the fitness of a pop.
Natural selection
causes adaptive evolution
beneficial alleles are sorted and favored by natural selection
Relative fitness
contribution of an individual makes to the gene pool of the next generation relative to the contributions of other individuals.
3 modes of natural selection
Directional selection: favors indiv at one end of the phenotypic range
Disruptive selection: favors indiv at both extremes of the phenotypic range
Stabilizing selections: favors intermediate variants and acts against ext. phenotypes
Intrasexual selection
competition among indv of one sex for mates of the opposite sex
Intersexual selections
aka mate choice, occurs when indiv. of one sex are choosy in selecting their mates.
maintains genetic variation in the form of hidden recessive allele.
Balancing selection
occurs when natural selection maintains stable freq of two or more phenotypic forms in a population