Microevolution
A change in allele frequencies in a population over generations, smallest scale of evolution
Three main mechanisms for allele frequency change
Natural selection, genetic drift (chance events that alter frequency), and gene flow (transfer of alleles between populations)
True or false: only natural selection consistently improves the match between organisms and their environment (adaptation)
True
True or false: Mendel set the stage for understanding the genetic differences in which evolution is based?
True
Genetic variation
Differences among individuals in the composition of their genes or other DNA sequences
True or false: genetic variation at the whole-gene level (gene variability) can be quantified as the average percentage of loci that are heterozygous?
True
Nucleotide variability
Genetic variation that can be measured at the molecular level of DNA, little results in phenotypic variation due to differences occurring within introns, variations in exons mostly due not change amino acid sequences of proteins in the gene
Introns
Non coding segments of DNA lying between exons
Exons
Regions retained in mRNA after RNA processing
Phenotype
Product of an inherited genotype and many environmental influences
True or false: genetic variation provides the raw material for evolutionary change?
True
True or false: without genetic variation evolution cannot occur?
True
Mutation
Change in the nucleotide sequence of an organism's DNA
Point mutation
Change of one base in a gene, results in significant impact on phenotype
True or false: due to the redundancy in the genetic code, even a point mutation in a gene that encodes a protein will have no effect on the proteins function if the amino acid composition is not changed?
True
True or false: a mutant allele on rare occasions may actually make its bearer better suited to the environment, enhancing reproductive success
True
Chromosomal changes the delete, disrupt, or rearrange many loci at once are usually
Harmful
The key potential source of variation is
The duplication of genes due to errors in meiosis
True or false: Mutation rates tend the below and plants and animals
True
Which organism has more generations per unit of time, resulting in higher mutations in populations?
Prokaryotes
What three mechanisms contribute to the shuffling of sexual reproduction?
Crossing over, Independent assortment of chromosomes, and fertilization
A group of individuals of the same species that live in the same area and interbreed producing fertile offspring
Population
Consists of all copies of every type of allele at every locus in all members of the population
Gene pool
What causes an allele to be fixed in the gene pool?
When only one allele exists for the particular locus in a population
True or false: If two or more alleles for a particular locus are in a population, individuals may be there homozygous or heterozygous
True
Proportion of a population
Frequency
Hardy Weinberg Principle
States that the frequencies of alleles and genotypes in a population will remain constant from generation to generation provided that only Mendelian segregation and recombination of alleles are at work
When is a population considered at the Hardy Weinberg equilibrium?
When the genotype frequencies are such that the actual frequency of one homozygote is p2 and the actual frequency of the other homozygote is q2 and the actual frequency of heterozygotes is 2pq
True or false:
The repeated shuffling of a populations gene pool over the generations cannot in itself change the frequency of one allele relative to another
Is it common for normal populations to be in the Hardy Weinberg equilibrium for only specific genes?
Yes, this apparent contradiction occurs because a population can be evolving at some loci yet simultaneously be in the Hardy Weinberg equilibrium at other loci
What is often used as the initial test for evolution occurring in a population?
The Hardy Weinberg equation
What is the concept of natural selection based on?
Differential success and survival and reproduction
Adaptive evolution
Evolution that results in a better match between organisms and their environment
Genetic drift
Chance events that can cause allele frequencies to fluctuate unpredictably from one generation to the next, especially in small populations
Allele frequencies are often affected by:
Survival, reproduction, and chance events that occur during fertilization
Founder effect
A smaller group established from a larger population that was isolated causing a new gene pool that differs from the original population source
Bottleneck effect
The severe drop in population size caused by sudden change in the environment, such as a fire or flood, that drastically reduces the size of the population
What happens to the genetic variation of a bottleneck effect population?
Certain alleles may be overrepresented among the survivors, others maybe underrepresented, and so maybe absent altogether. Even if a population that has passed through bottleneck ultimately recovers in size it may have low levels of genetic variation for
Effects of genetic drift
1. Genetic drift is significant in small populations
2. Genetic drift can cause allele frequencies to change at random
3. Genetic drift can lead to a loss of genetic variation within populations
4. Genetic drift can cause harmful alleles to become fixed
Gene flow
The transfer of alleles into or out of the population due to the movement of fertile individuals or their gametes
Can a gene flow result in two populations combining into one?
Yes, because alleles are transferred between populations gene flow tends to reduce the genetic differences between populations, which can result populations combining into one with a common gene pool
True or false: gene flow can also transfer alleles that improve the ability of populations to adapt to local conditions
True
Adaptive evolution
Natural selection consistently increasing the frequencies of alleles that provide reproductive advantages
Relative fitness
Contribution an individual makes to the gene pool of the next generation relative to the contribution of other individuals
Directional selection
When conditions favor individuals at one extreme of a phenotypic range, thereby shifting a populations frequency curve for the phenotypic character in one direction or the other
Directional selection is common when:
A populations environment changes or when members of a population migrate to a different habitat
Disruptive selection
Conditions favor individuals at both extremes of a phenotypic range over individuals with intermediate phenotypes
Stabilizing selection
Acts against both extreme phenotypes and favors intermediate variants, reducing variation and maintains the status quo for a particular phenotypic character
True or false: selection favors individuals whose heritable phenotypic traits provide lower reproductive success than the traits of other individuals
False, favor traits for higher reproductive success
What makes adaptive evolution a continuos dynamic process?
The physical and biological components of an organisms environment change over time making the "good match" between an organism and its environment a moving target
Sexual selection
Form of natural selection in which individuals with certain inherited characteristics are more likely than other individuals to obtain mates
Sexual dimorphism
Difference in secondary sexual characteristics between males and females of the same species, distinctions include differences in size, color, ornamentation, and behavior
Intrasexual selection
Selection within the same sex, meaning individuals of one sex compete directly for mates of the opposite sex
Intersexual selection
Mate choice, individuals of one sex are choosy in selecting their mates from the other sex, usually depending on the showiness of the males appearance or behavior
Neutral variation
Differences in DNA sequence that do not confer a selective advantage or disadvantage
Diploid organisms
Organisms in which a considerable amount of genetic variation is hidden from selection in the form of recessive alleles
Balancing selection
Occurs when natural selection maintains two or more forms in a population, includes heterozygote advantage and frequency dependent selection
Heterozygote advantage
Individuals who are heterozygous at a particular locus have greater fitness than do both kinds of homozygotes, defined in terms of genotype not phenotype
Frequency dependent selection
Fitness of a phenotype depends on how common it is in the population