Biology Lecture 3 - Exam 1
Biology Lecture 3 - Exam 1 BIO 121 A
Popular in General Biology
Popular in Biology
This 5 page Class Notes was uploaded by Devin Mart on Tuesday March 29, 2016. The Class Notes belongs to BIO 121 A at Missouri State University taught by Dr. Durham in Spring 2016. Since its upload, it has received 10 views. For similar materials see General Biology in Biology at Missouri State University.
Reviews for Biology Lecture 3 - Exam 1
Report this Material
What is Karma?
Karma is the currency of StudySoup.
Date Created: 03/29/16
Mart 1 Lecture 3: The Evolution of Populations ● A population, not its’ individuals, evolve (it evolves as a whole). ○ Evolution on scale of populations is due to microevolution evolutionary change within a species or small group of organisms, especially over a short period. ○ Population genetics is the study of the distribution and change in frequency of alleles within populations. ■ This emphasizes extensive genetic variation within populations and recognizes importance of quantitative characters. ○ Modern synthesis emphasizes: 1. The importance of populations as the units of evolution. 2. The central role of natural selection as most important mechanism of evolution. 3. The idea of gradualism to explain how large changes can evolve as an accumulation of small changes over long periods of time. ● A population is a localized group of individuals that belong to the same species. ○ A species is a group of populations whose individuals have the potential to interbreed and produce fertile offspring in nature. ○ Members of a population are more likely to breed with members of same population than with members of other populations ● A gene pool is the stock of different genes in an interbreeding population. ○ All allelesat the gene loci in all individuals of a population. ○ Each locus is represented twice in a genome of a diploid (of a cell or nucleus) containing two complete sets of chromosomes, one from each parent. ■ Individuals can be homozygous or heterozygous for these homologous loci. ● The HardyWeinberg Theorem states that allele and genotype frequencies in a population will remain constant from generation to generation in the absence of other evolutionary influences. ○ Populations at HardyWeinberg equilibrium must satisfy 5 conditions: 1. Very large population size in small populations, chance fluctuations in a gene pool can cause genotype frequencies to change over time. 2. No migrations gene flow, transfer of all alleles due to the movement of individuals or gametes into or out of our target population can change the proportions of alleles. 3. No net mutations if one allele can mutate into another, the gene pool with be altered. 4. Random mating if individuals pick mates with certain genotypes, then the mixing of gametes will not be random and the HardyWeinberg equilibrium does not occur. Mart 2 5. No natural selection if there is differential survival or mating success among genotypes, the frequencies of alleles in next variation will deviate from frequencies predicted by HardyWeinberg equation. ○ Evolution usually results when any of these five conditions are not met, when a population experiences deviations from the stability predicted by the HardyWeinberg theory. ● Microevolution is the generation to generation change in a population’s frequencies of alleles. ○ Four factors can alter allele frequencies in a population: 1. Genetic drift 2.Natural selection 3.Gene flow 4. Mutation ● Genetic drift occurs when changes in gene frequencies from one generation to another occur because of chance events (sampling errors) that occur when populations are finite in size. ● Bottleneck effect occurs when number of individuals in a larger population are drastically reduced by a disaster. ○ Some alleles are overrepresented, other underrepresented, some entirely eliminated. ○ This is an important concept in conservation biology of endangered species. ● Founder effect is when a new population is started by only a few individuals and a gene pool of a larger source population is not represented. ○ Demonstrated in human populations that started from a small group of colonists. ● Gene flow is a genetic exchange due to migration of fertile individuals or gametes between populations. ○ Migration of people throughout the world is transferring alleles between populations that were once isolated, increasing the gene flow. ● A m utation is a change in an organism’s DNA. ○ Generally there is not much quantitative effect on large population in a single generation. ○ A long term mutation is important to evolution, the original source of genetic variation that serves as raw material for natural selection. ● Genetic variation occurs within and between population. ○ Variation in a population is because of a combination of inheritable and noninheritable traits. ○ Phenotype are observable characteristic of an organism, a product of inherited genotype and environment influences. ■ Example: Genetically identical at coloration loci emerge at different seasons. ○ Only genetic component of variation is evolutionary consequences is a result of natural selection. Mart 3 ■ Only inheritable traits pass from generation to generation. ○ Variation within a population can be both quantitative and discrete characters. ■ Quantitative characters vary along a continuum within a population. ● Example: plant height in wildflower population. ● This is usually due to polygenic inheritance the additive effects of two or more genes influence a single phenotypic character. ■ Discrete characters are usually determined by a single locus with different alleles, this has a distinct impact on phenotypes. ● Polymorphism occurs when two or more discrete characters are present and noticeable in a population. ○ Population geneticists measure genetic variation the level of whole genes and the molecular level of DNA. ● Gene diversity is the average percent of gene loci that are heterozygous. ● Nucleotide diversity is the level of difference in nucleotide sequences among individuals in a population. ● Geographic variation results from differences in genetic structure between populations or between subgroups of a single population inhabitants of different areas. ○ This results from natural selection or genetic drift. ○ Geographic variation in form of graded change in a trait along a geographic axis is a cline ■ Example: the average body size of many North American species of birds and mammals increases with higher latitudes. ○ In contrast to clines, isolated populations typically demonstrate discrete differences.. ■ Example: house mice isolate populations developed, some evolved differences in karyotypes probably through genetic drift. ● Mutation and sexual recombination generate genetic variation . ○ New alleles originate only by mutation. ■ Most point mutations only affect a single bases, usually harmless. ■ Mutations alter protein structure/function and are more likely to be harmful than beneficial. ■ Chromosomal mutations affect many genes, likely to disrupt proper development of an organism. ■ Duplications of chromosome segments, whole chromosomes, or sets of chromosomes are nearly always harmful. ○ Because microorganisms have very short generation times, mutation generates genetic variation rapidly. Mart 4 ○ Organisms sexual reproduction, most of the genetic differences are due to unique recombinations of existing alleles from the population gene pool, ultimate origin of allelic variation is past mutations. ● Diploidy and balanced polymorphism preserve variation. ○ Tendency for natural selection to reduce variation is countered by mechanisms that preserve or restore variation diploidy and balanced polymorphisms. ■ Diploidy is eukaryotes prevents elimination of recessive alleles by selection because they do not impact the phenotype in heterozygotes. ○ Balanced polymorphism maintains genetic diversity in a population via natural selection. ■ 1st mechanism heterozygote advantage heterozygous at particular locus have greater survivorship and reproductive success than homozygotes. ■ 2nd mechanism frequency dependent selection occurs when reproductive success of any one morph declines if phenotype becomes too common in population. ● Natural selection as the mechanism of adaptive evolution. ○ Adaptive evolution is a trait with a current functional role in the life of an organism that is maintained and evolved by means of natural selection. ■ Chace creates new genetic variations by mutation and sexual recombination. ■ Sorting by natural selection favors propagation of some variations over others, this produces organisms that are a better fit to their environments. ○ Evolutionary fitness is the relative contribution that an individual makes to the gene pool of the next generation. ■ Reproduction success depends on a variety of factors. ■ Example: slight differences in flower shape, color, or fragrance may lead to differences in reproductive success. ○ Darwinian fitness a contribution an individual makes to the gene pool of the next generation relative to contributions of other individuals. ○ Relative fitness contribution of one genotype to the next generation compared to contributions of alternative genotypes for the same locus. ■ Survival alone does not guarantee reproductive success many factors affect both survival and the determination of evolutionary fitness. ■ Through differential survival and reproductive success of phenotypes, natural selection adapts a population to its environment by increase or by maintaining favorable genotypes that produce better phenotypes in the gene pool. ● Natural selection affects frequency of a heritable trait in a population leading to: Mart 5 ○ Directional selection most common during periods of environmental change or when members of a population migrate to a new habitat with different environmental conditions. ○ Diversifying selection occurs when environmental conditions favor individuals at both extremes of the phenotypic range over intermediate phenotypes. ○ Stabilizing selection favors intermediate variants and acts against extreme phenotypes, this reduces variation and maintains predominant phenotypes. ● Natural selection maintains sexual reproduction. ○ Sex is an evolutionary enigma, inferior to asexual reproduction as measured by reproductive output (number of individuals that can reproduce). ○ Sex must confer some selective advantage to compensate for costs of diminished reproductive output. ■ Most eukaryotes maintain sex, even in species that can reproduce asexually. ■ Sex provides a mechanism for changing the distribution of alleles and varying them among offspring. ○ Reasons why natural selection cannot produce perfection: 1. Evolution is limited by historical constraints. 2. Adaptations are often compromises. 3. Not all evolution is adaptive. 4. Selection can only edit existing variations.