Chapter 23 Flashcards
Microevolution
Evolutionary change below the species level; change in allele frequencies in populations over generations
3 main mechanisms that cause change in allele frequencies
1) Natural selection
2) genetic drift
3) gene flow
Genetic Variation
Differences among individuals in the composition of their genes/DNA sequences
Introns
Non coding segments of DNA lying between exons
Exons
Regions retained in mRNA after RNA processing
Without genetic variation…
Evolution cannot occur
Neutral Variation
Result of point mutation, genetic variation that doesn’t provide a selective advantage or disadvantage
Point mutation
A very small mutation, such as a change in one base in a gene
Gene pool
The aggregate of all copies of every type of allele at all loci in every individual in a population
Adaptive evolution
A process in which traits that enhance survival/reproduction tend to increase in frequency over time
Generic drift
Chance events cause unpredictable fluctuations in allele frequencies from one generation to the next
Founder effect
Genetic drift that occurs when few individuals become isolated from a larger population and form a new population who’s gene pool doesn’t reflect original population
Bottleneck effect
Genetic drift that occurs when the size of a population is reduced by natural disasters or human effect. Surviving population usually doesn’t reflect original population
Genetic drift is..,
1) significant in small populations
2) cause alleles to change at random
3) lead to a loss of genetic variation within populations
4) cause harmful allele to become fixed
Gene flow
Transfer of alleles from one population to another, resulting from movement of fertile individuals or their gamates
Relative fitness
Contribution an individual makes to the gene pool of the next generation
Directional selection
Form of natural selection in which individuals at one end of phenotypic range survive or reproduce more then others
Disruptive selection
Natural selection in which individuals on both extremes of a phenotypic range survive or reproduce more then Individuals with intermediate phenotypes
Stabilizing selection
Natural selection in which intermediate phenotypes survive or reproduce more then extreme phenotypes
Sexual selection
Process in which individuals with certain inherited characteristics are more likely to obtain mates then others of the same sex
Sexual dismorphism
Differences between the secondary sex characteristics of males and females of same species (think male female peacocks)
Intrasexual selection
Direct competition between the same sex to find a mate
Intersexual selection
Individuals of one sex (usually females) are very choosy in selecting opposite sex mate (aka mate choice)
Balancing selection
Natural selection that maintains two or more phenotypic forms in a population
Frequency-dependent selection
Selection in which fitness of phenotype depends on how common the phenotype is in population
Heterozygote advantage
Greater reproductive success of heterozygous individuals compared to homozygous
