Chapter 4: Genes And Their Evolution: Population Genetics

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Deme

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A local population of organisms that have similar genes, interbreed, and produce offspring. A population of organisms that are closely related.

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Gene pool

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All genetic information in the breeding population.

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Reproductive isolation

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Any circumstance that prevents two populations from interbreeding and exchanging genetic material, such as when two populations are separated by a large body of water or a major mountain range.

In biological terms if two populations are reproductively isolated, members of one population cannot interbreed with members of the other. This is largely related to geographic isolation. If 2 populations of the same species become isolated by geographic changes then enough genetic differences can accumulate to create two different species.

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Microevolution

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Small-scale evolution, such as changes in allele frequency, that occurs from one generation to the next.

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Macroevolution

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Large-scale evolution, such as speciation event, that occurs after hundreds or thousands of generations.

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Equilibrium

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There are instances in which frequency does not change over time -that is, when the frequencies of a population's alleles for a particular trait are in a state of equilibrium.

Equilibrium is the condition in which the system is stable, balanced, and unchanging.

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Hardy Weinberg Law of Equilibrium

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A mathematical model in population genetics that reflects the relationship between frequencies of alleles and genotypes; it could be used to determine whether a population is undergoing evolutionary changes.

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What might cause a population to change it's allele frequencies amd go out of equilibrium?

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Mutation, natural selection, gene flow, genetic drift

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What is the only source of new genetic variation in a population?

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Mutations are the only source of new genetic variation in a population.

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Point mutations

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Replacements of a single nitrogen base with another base, which may or may not affect the amino acid for which the triplet codes.

Incorrect base pairings

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Synonymous point mutation

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A nuetral point mutation in which the substituted nitrogen base creates a triplet coded to produce the same amino acid as that of the triplet.

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Nonsynonymous point mutation

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A point mutation that creates a triplet coded to produce a different amino acid from that of the original triplet.

There is usually an insertion or deletion of a single nucleotide in the sequence during transcription when the messenger RNA is copying the DNA.

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Frameshift mutation

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The change in gene due to the insertion or deletion in one or more nitrogen bases, which causes the subsequent triplets to be rearranged and the codons to be read incorrectly during translation.

It produces a protien that has no function.

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Transposable elements

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Mobile pieces that can copy themselves into entirely new areas of the chromosomes.

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Spontaneous mutations

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Random changes in DNA that occur during cell division

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Induced mutations

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Refers to those mutations in the DNA resulting from exposure to toxic chemicals or radiation.

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Mutagens

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Substances such as toxins, chemicals, or radiation that may induce genetic mutations.

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Klinefelter's syndrome

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A chromosomal trisomy in which males have an extra X chromosome, resulting in an XXY condition; affected individuals typically have reduced fertility

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Directional selection

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Selection for one allele over the other alleles, causing the allele frequencies to shift in one direction

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Stabalizing selection

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Selection against the extremes of the phenotypic distribution, decreasing the genetic diversity for this trait in the population.

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Disruptive selection

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Selection for both extremes of the phenotypic distribution; may eventually lead to a speciation event.

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Fitness

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Average number of offspring produced by parents with particular genotype compared to the number of offspring produced by parents with another genotype

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Positive selection

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Process in which advantageous genetic variants quickly increase in frequency in a population.

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Sickle-cell anemia

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A genetic blood disease in which the red blood cells become deformed and sickle-cell shaped, decreasing their ability to carry oxygen to tissues.

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Hemoletic anemias

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Conditions of insufficient iron in the blood due to the destruction of red blood cells resulting from genetic blood diseases, toxins, or infectious pathogens.

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Abnormal hemoglobin

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Hemoglobin altered so that it is less efficient at binding to and carrying oxygen.

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Capillaries

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Small blood vessels between the terminal ends of arteries and the viens.

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Balanced polymorphism

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The genetic selective scenario in which a heterozygote for two alleles of a gene has an advantage over either of the homozyous states

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Hemobloginopathies

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A group of related genetic blood diseases characterized by abnormal hemoglobin.

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Thalassemia

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A genetic blood disease in which the hemoglobin in imptoperly synthesized causing the red blood cells to have a much shorter lifespan.

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Endogamous

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Refers to a population in which individuals breed with only nonmembers of their population.

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Exogamous

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Refers to a population in which individuals breed only with nonmembers of their population

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Genetic drift is more likely to occur...

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Within a smaller population

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Founder effect

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One form of genetic drift. It occurs when a small group (fewer than several hundred members) of a large parent population migrates to a new region and is reproducticely isolated. Because the founding population is so small, there is a very good chance that its genetic composition is not representative of the parent's population. As the founding population grows, it's gene pool diverges even furrher from the source.

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Hunington's chorea

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A rare genetic disease in which the central nervous system degenerates and the individual loses control over voluntary movements, with the symptoms appearing between ages 30 to 50.

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Admixture

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The exchange of genetic material between two or more populations.

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Gene flow

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•the key determinant for the amount of gene flow in accessibility to mates -the less the physical distance between populations, the greater the chance of gene flow

•while mutations increase genetic variation between two populations over time, gene flow decreases such variation