Biology Final Review > Chapter 23 - Evolution of Populations > Flashcards
Chapter 23 - Evolution of Populations Flashcards
inter
between
intra
within
micro
small
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poly
many
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Average heterozygosity
The percent, on average, of a population’s loci that are heterozygous in members of the population.
Bottleneck effect
Genetic drift resulting from the reduction of a population, typically by a natural disaster, such that the surviving population is no longer genetically representative of the original population.
Cline
A graded variation in a trait that parallels a gradient in the environment.
Founder effect
Genetic drift that occurs when a few individuals become isolated from a larger population, with the result that the new population’s gene pool is not reflective of the original population.
Gene flow
Genetic additions to or subtractions from a population resulting from the movement of fertile individuals or gametes.
Gene pool
The total aggregate of genes in a population at any one time.
Gene variability
The percentage of loci in a population that are heterozygotes
Genetic drift
Unpredictable fluctuations in allele frequencies from one generation to the next because of a population’s finite size.
Geographic variation
Differences between the gene pools of separate populations or population subgroups.
Hardy-Weinberg equilibrium
The condition describing a non-evolving population (one that is in genetic equilibrium).
Intersexual selection
Selection whereby individuals of one sex (usually females) are choosy in selecting their mates from individuals of the other sex; also called mate choice.
Intrasexual selection
A direct competition among individuals of one sex (usually the males in vertebrates) for mates of the opposite sex.
Microevolution
Evolutionary change below the species level; change in the genetic makeup of a population from generation to generation.
Mutation
A rare change in the DNA of a gene, ultimately creating genetic diversity.
Nucleotide variability
The amount of differences in a population of all nucleotides possibilities at given gene loci.
Population
Localized group of individuals who are capable of interbreeding and producing fertile offspring.
Relative fitness
The contribution of one genotype to the next generation compared to that of alternative genotypes for the same locus.
Sexual dimorphism
A special case of differences between individuals based on the distinction between the secondary sex characteristics of males and females.
Microevolution is the change in actual allele frequency in populations over generations
o Looks at only individual allele changes, not in overall speciation patterns
Microevolution can occur by 3 mechanisms
- Natural selection
- Genetic drift
- Gene flow
Evolution requires populations have genetic variation which can be measured by
o Gene variability of how many loci in a given population are heterozygotes
o Nucleotide variability which measures the overall difference in nucleotide sequences between individuals in a population
o If an allele becomes fixed, there is only one version for that gene (i.e. all homozygotes for that loci)
Causes of genetic variation
o Geographic: Populations can differ because of geographic separation which is a cause of geographic variation in genetic material
Clines are gradual changes in geography that can cause gradual changes in genetic differences of the individuals along the cline
o Mutation of single base pairs or larger segments of DNA repeats or chromosomal organization
o Events in meiosis such as crossing over and independent assortment
o Random fertilization
The Hardy Weinberg Equation allows us to determine if a population is evolving
o The theory assumes there are 2 alleles for a given loci so that a population in Hardy Weinberg Equilibrium can be represented by the equation:
p2+ 2pq + q2 = 1 with the frequency of p and q representing the allele frequencies with p2 = the frequency of homozygotes of one allele, q2 is the frequency of the other homozygotes and 2pq is frequency of the heterozygotes
o For a population to be in Hardy Weinberg Equilibrium, no evolution is occurring so this means: No mutations Random mating No natural selection Extremely large population size No gene flow
Natural selection
will cause adaptive changes in allele frequencies and thus evolution
Genetic drift is the change in gene frequency caused by random chance events that have no adaptive value in increasing or decreasing certain allele’s frequency
o Genetic drift can often lead to a loss of genetic variation in a population as certain alleles become fixed even if they do not have an adaptive advantage
o Two example of genetic drift caused by small populations
Founder Effect: Relatively small group of individuals that break off from original larger populations and may have a non-representative allele frequency
Bottleneck Effect: Dramatic and quick reduction in population size in which certain alleles may be present that don’t represent the original allele frequency
Gene flow can also alter allele frequencies in populations but allowing interchange of alleles between populations
o Generally, gene flow reduces the genetic variation between populations
Relative fitness
refers to how well an individual is able to contribute to the gene pool compared to other individuals—with the assumption they will contribute MORE if are better adapted
Sexual selection is a specific type of selection that favors mating success
o Could drive differences between the sexes called sexual dimorphism
o Intrasexual selection is competition within the same sex such as 2 males fighting for dominance
o Intersexual selection involves mate choice when one gender selects his or her mate based on certain characteristics
What are the 3 mechanism for microevolution? Briefly describe what they are.
Three mechanisms for microevolution (which is a change in allele frequency in a population over generations) are 1.) Natural selection. 2.) Genetic drift and 3.) Gene flow.
In natural selection, due to genetic variation in the population, certain individuals will have inherited traits that contribute to their increased survival and reproduction. By reproducing more, these alleles are preferentially passed on more to the next generation.
In genetic drift, chance events can alter allele frequency. The chance part implies that there is no particular advantage for one allele persisting and another not, outside factors that are not specifically selecting for one allele over another affect allele frequency.
In gene flow, alleles are passed between populations which can then alter the frequency of existing alleles. This transfer generally decreases the general genetic variability between populations.
What are the 2 types of genetic variation? What mechanisms account for genetic variation in sexual reproduction?
Genetic variability can be measured both at the whole gene level (gene variability) or on a more precise scale of nucleotide variability. For gene variability, the important measure is how many individuals in a population are heterozygotes which allows for the possibility of the passing of different alleles to offspring. Homozygous individuals only have one version of the gene therefore, their offspring have a lower genetic variability possibility.
For nucleotide variability, the comparison is how different the actual DNA nucleotide sequence may be between individuals in a population. This variability might not show up in actual phenotypes due to redundancy in the genetic code or if the nucleotide differences occur in non-coding areas of the genome. Mutations can introduce genetic variability but in sexually reproducing organism that form their gametes through meiosis,
there are 3 methods which can increase genetic variation: crossing over (exchange of genes between non-sister chromatids of homologous pairs), independent assortment of pairs of homologues leading to novel combinations of overall chromosomes inherited from parents and finally random fertilization which combines the genetic material from a male and female into a new offspring.
Define a cline and how geographic variation occurs alone the cline.
When populations are separated by geographic features such as islands or canyons, their genetic makeups can start to diverge. Sometimes, the divergence is a more gradual process as natural selection acts on different zone within the geographic area.
A cline is a graded change in a character along this geographic axis. For example, from the base of a mountain to the top, there is a slow decrease in average temperatures and while there may not be a complete barrier to individuals that live along the slope of the mountain, they will have different adaptive pressures put on them living in different climates which can manifest itself in genetic variation along the mountain slope.
How can you use the Hardy-Weinberg equation to determine allele frequencies in a gene pool?
The Hardy-Weinberg equation is p2 + 2pq + q2 = 1 where p and q represent the frequencies of the only 2 possible alleles in a population at a particular locus. You can use this equation to determine the allele frequencies in a population based on observed phenotypes for the gene involved.
What are the 5 conditions necessary in a population which uphold Hardy-Weinberg equilibrium?
The Hardy-Weinberg theorem assumes that a population is NOT evolving which implies there are no mutations in the genomes of the population only random mating occurs (therefore no mate selection), no natural selection that the population is very large to avoid chance events from having any influence and that there is no gene flow in and out of the populations. In reality, it would be virtually impossible for all these conditions to be met so we can use the Hardy Weinberg allele frequencies to compare populations over time and see how those frequencies have changed in populations which is evidence for evolution.
How does the founder effect and genetic bottlenecks affect genetic drift?
Genetic drift occurs because random events (and not natural selection) may influence the allele frequencies in population.
The founder effect is one example of genetic drift in which a few individuals in a population may become isolated from the larger gene pool. By chance, only the alleles present in those founder individuals will be present in the new, smaller gene pool. If no gene flow occurs between the founder population and larger, parent population, the genetic differences will continue between the 2 populations.
A similar effect is seen with a genetic bottleneck in which some chance event eliminates many individuals in a population in a given area and the surviving individuals will possess only their alleles which will be generally lower in variability compared to the original, larger population.
How does gene flow effect genetic variation in a gene pool?
Gene flow is the movement of alleles among populations.
Sometimes alleles are moved by whole animal migration such as what frequently occurs in some animal populations when members who reach sexual maturity leave their natal group and move to another geographic area, bringing their alleles with them.
Sometimes it is only the gametes that disperse such as pollen spreading on the wind or by pollinators to new areas.
In either case, sometimes the addition of new alleles will give a potential advantage to the new population and therefore natural selection will increase the frequency of that allele over time in the new population.
Overall however, gene flow tends to reduce the overall amount of genetic variability between populations if they are allowed genetic exchange.
Distinguish between intrasexual and intersexual selection. How does sexual dimorphism occur in sexual selection?
Intrasexual selection is competition within the same gender for mates of the opposite sex. In most species, it is the males who compete but it can be females. Many male have elaborate bluffing challenges and sometimes outright physical confrontations to gain the right to mate with a female or females in the area.
Intersexual selection or mate choice is when individuals, usually females, are choosy in selecting their mates. Mating is not random and females choose some males and reject others so not all males have an opportunity to mate. Some males have developed complex mating rituals to show potential mates their relative fitness to mate with the implication that they have the strength and vigor to demonstrate these displays and therefore have overall superior fitness.
