Biology Chapter 15 Lecture Notes PDF

Preview

Summary

Lecture Notes from chapter 15 of BIOL101, taught by Serena Gross, PhD during the fall 2018 semester at Ivy Tech Community College...

Description

Chapter 15: Evolution on a small scale 1. Natural Selection is the process that results in adaptation of a popoularion to the biotic (living) and abiotic (nonliving) components of the environment a. Organisms acquire resources through competition, predation or parasitism b. Abiotic components are things like weather conditions temperature and precipitation c. As a result of natural selection, the most fit individuals for a particular environment become more prevalent in the population, causing the population to change over time d. The most fit individuals are the ones that reproduce more than others and have offspring that survive to reproduce e. These are generally the individuals that are most suited to the environment 2. Types of selection a. For many traits there are multiple alleles that produce a range of phenotypes b. An individual’s phenotype is the observable trait of an individual that results from the interaction of the individuals genotype and the environment c. Distribution of phenotypes in an environment often resembles a bell curve 3. Stablizing selection a. Stabilization selection occurs when an intermediate phenotype is favored b. Extreme phenotypes are selected against c. Individuals near average are favored d. Most common because average individuals are generally well adapted to their environment

4. Directional Selection a. Directional selection occurs when an extreme phenotype is favored b. The distribution curve shifts in the direction of the favored phenotype c. Can occur when adapting to a new environment d. Examples: resistance to antibiotics in bacteria 5. Disruptive Selection a. In disruptive selection two or more extreme phenotypes are favored over intermediate phenotypes i. Favors polymorphism b. Polymorphism is the occurrence of different forms in a population of the same species c. Different phenotypes adapted to their area of the environment both exist in a population 6. Sexual Selection a. Sexual selection refers to adaptive changes in males and females that lead to an increased ability to reproduce and produce offspring 7. Adaptations aren’t perfect a. Natural selection doesn’t always produce organisms that are perfectly adapted to their environment b. Evolution doesn’t start from scratch, has to work with available variations c. As adaptations are evolving in a population, the environment may also be changing as are other species in a population d. Compromises are necessary

e. Ability to use hands as bipedal organism is extremely beneficial but spines were not originally meant to be upright 8. Maintenance of Variations a. Populations always show some genotypic variation b. Variation is beneficial for adapting to changes in the environment or with predators or prey c. If a population cant change, it is likely to become extinct d. Variation is always at work i. Mutation generates new alleles ii. Fertilization creates new combinations of alleles iii. Gene flow between populations 9. Heterozygote Advantage a. Only alleles that are expressed, the phenotype, are subject to natural selection b. Heterozygotes potentially protect recessive alleles c. Allows the possibility of recessive phenotype being shown, which may be advantageous if conditions change d. When environmental conditions cause two phenotypes to be maintained it is called balanced polymorphism i. Sickle-cell disease 10. Microevolution a. Many traits change temporarily in response to a varying environment b. Changes to traits over an individuals lifetime are not evidence of evolution c. Only heritable traits can evolve

d. Evolution causes change in a heritable trait within a population, not an indivual e. Populations, not individuals, evolve f. Genes interact with the environment to determine traits g. Evolution is about genetic change 11. Evolution in a genetic context a. In population genetics the various alleles at all loci in all individuals make up the gene pool of the population b. The genotype frequency is the percentage of a specific genotype in a population c. Allele frequency is how much a specific allele is represented in the gene pool of a population d. Random sexual reproduction alone cannot bring about change in genotype and allele frequency 12. Examples of Evolution a. For genotype frequencies to be subject to natural selection they must result in a change of phenotype frequencies b. Industrial melanism is an increase in the frequency of a dark phenotype due to pollution i. Natural selection can act in a short period of time 13. Factors that cause Evolution a. Mutations – Allele changes i. Permanent genetic changes ii. Raw material for evolutionary change iii. Rate of mutations is generally very low

iv. Many mutations are neutral 1. They are not selected for or against v. Prokaryotes do not reproduce sexually and are more dependent on mutations to introduce variation b. Gene flow – migration of alleles into or out of the population i. Also called gene, migration, is the movement of alleles among populations by migration of breeding individuals ii. Can increase the variation within a population by introducing novel alleles produced by mutation in another population iii. Gene flow can prevent specification from occurring 1. Subspecies – different populations of the same species with distinctive characteristics or a barrier to breeding c. Non-random mating – Individuals are more likely to pair based on their phenotypes i. Random mating occurs when individuals select mates by chance ii. Non-random mating occurs when individuals select mates by phenotypic differences or when certain phenotypes are more likely to breed iii. Inbreeding, mating between relatives, is an example of non-random mating iv. Assortative mating occurs when individuals tend to mate with those that have the same phenotype v. Assortative mating causes populations to subdivide into different phenotypic classes

1. Gene exchange is reduced vi. Sexual selection favors characteristics that increase the likelihood of obtaining mates, promoting non-random mating d. Genetic drift – changes in allele frequency i. Refers to the changes in the allele frequencies of a gene pool due to chance ii. Allele frequencies drift over time depending on which individuals reproduce iii. Small populations are more susceptible to changes in genotypes iv. Bottleneck Effect 1. Sometimes a species is subject to near extinction due to something such as a natural disaster, habitat loss, or overharvesting 2. Only a few survivors, as though they have passed through the neck of a bottle 3. The bottleneck effect prevents the majority of genotypes from reproducing 4. Causes genetic similarity between survivors 5. Genetic drift can cause certain alleles to be lost from a population 6. Cheetahs are extremely genetically similar, likely due to a genetic bottleneck a. This means they are inbred v. Founder effect

1. The founder effect is a mechanism of genetic drift in which rare alleles or combinations of alleles occur at a higher frequency in a population isolated from the general population 2. Founding individuals carry only a fraction of the genetic diversity of the original gene pool 3. Alleles carried by a founder or founders are likely by chance alone e. Selection – natural selection favors an allele...