BIO 203L- Lecture 5
BIO 203L- Lecture 5 BIOL 203L 005
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This 6 page Class Notes was uploaded by Karissa Sandoval on Thursday January 28, 2016. The Class Notes belongs to BIOL 203L 005 at University of New Mexico taught by Dr. Kelly Miller and Dr. Scott Collins in Spring 2016. Since its upload, it has received 23 views. For similar materials see Ecology and Evolution Laboratory in Biology at University of New Mexico.
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Date Created: 01/28/16
BIO 203: Evolution Lecture 5 Random Evolution, Non-Random Mating •Gene Flow – Hardy-Weinberg Equilibrium requires a closed system (isolated) – Gene flow – movement of alleles between populations – Generally results in homogenizing alleles (equalizing allele frequencies) between populations (mixing) – Random with respect to fitness • Alleles conferring both low fitness and high fitness can move between populations •Variation – Variation is key to evolution – Populations can’t change without variation – Variation is the substrate for natural selection •Sources of variation – Recombination (Sex) • Reshuffling of alleles in sexual reproduction • Does not change frequency of alleles, but does change which alleles are combined (provides opportunities for new combinations) – Putting them together in different ways • Many phenotypes result from combinations of multiple alleles – selection of one feature selects for multiple alleles – Sex is combining things together and mitotic errors causes new phenotypes – Gene transfer • Horizontal gene transfer – incorporation of alleles from other organisms – Ways to incorporate alleles from other organisms: • Transformation – absorption of environmental DNA • Organisms can absorb any DNA from the outside and make them apart of their DNA • Conjugation – Plasmids, Small circular pieces of DNA passed between bacteria • Transduction – Viruses may move DNA, including genes, horizontally • Mitochondria, chloroplasts – entire genomes from bacteria – Individual cells that were incorporated to the eukaryotic cell from the prokaryotic cell • Gene duplication – Chromosome mutation – Wholesale duplication of a region with an entire gene – Original copy continues to function BIO 203: Evolution Lecture 5 – New copy is free to mutate (free from selective pressures) – Can be a duplication of the entire genome • E.g. wheat has 6 copies of its genome (polyploid) – Mutation • Errors in DNA replication in gamete-producing cells create change in DNA sequences and novel alleles – Mutations in a gamete producing cell (sperm or egg) or gamete cell. Which are to be random, will be passed on genetically • Random – not subject to selection • Most mutations in functional genes are deleterious (alleles that lower fitness) (bad) • Some mutations that increase fitness • Mutation (mainly subsequent to gene duplication) is the source of new alleles and new variation •Evolution – What is evolution? • Descent with modification • Mechanisms of modification – Natural selection – Random changes (genetic drift) – Sources of variation •What evolution is not – Not goal-directed • Evolution is a “tinkerer” not an “engineer” – Use what is available not designing and adding new valuables – Constraints (cant do what it wants) • Genetic correlation – Any allele that affects one feature likely affects other features – Example: Genes affecting size of one feature often affect the size of other features as well (selection of each feature may be in opposite directions) • Bigger ears make it easier to hear predator but it affects the size of legs so it makes it harder to run away quickly from the predator – Alleles may be linked on a chromosome, and can only be inherited together – Lack of variation • Selection can only work on variation… if variation doesn’t exist, evolution can’t happen BIO 203: Evolution Lecture 5 • Reason why bottlenecks make populations less adaptable (no variation in bottleneck populations so they cannot adapt to the environment) • Fitness trade offs – Fitness trade-off – compromise between features in how those traits perform in the environment – Example 1 – size • Large size may help in taking down prey • But large size may require more energy, and when food is scarce, large size may result in risk of starvation – Example 2 – sickle-cell anemia • Helps with malaria resistance • But results in anemia in low-oxygen situations – Every adaptation is a compromise • Historical constraints – Phylogeny – Organisms are limited to mutations within the context of sets of features inherited from their ancestors (subset of lack of variation) •Outline, Nonrandom mating – Hardy-Weinberg Equilibrium requires panmixia (random mating) – Mating is rarely random, so what about nonrandom mating? • Two ways: – Assortative mating –individuals choose partners like themselves (positive assortative mating) or different from themselves (negative assortative mating) • Negative assortative mating • Opposites attract • Example: Self-incompatibility in many angiosperms • Cannot self-fertilize • Encourages diversity of alleles (disruptive selection) • Positive assortative mating (Inbreeding) BIO 203: Evolution Lecture 5 • • Inbreeding – mating between relatives • They don’t have to be your relatives they could just have similar features • E.g. when dispersal is a problem (mating by availability because you are not dispersed to the world) • Extreme example – selfing (self- fertilization or cloning yourself) • Leads to Inbreeding depression (results from positive assortative mating) • Lower overall diversity (only alleles in family so the gene pool is limited) • Increased homozygosity and frequency of certain recessive alleles • Reduced overall fitness • (Just like bottlenecks and founder effect) *founder effect is the same thing as inbreeding depression* • Inbreeding • Example: Vadoma tribe in Zimbabwe • Can only marry within the tribe but they end up with two toes because of heavy inbreading • Ectrodactyly is common • An autosomal dominant disorder (due to recent mutation) • Example: House of Habsburg, Habsburg Jaw and other things BIO 203: Evolution Lecture 5 • Charles II of Spain could not chew properly • His jaw was due to mutation because of heavy interbreeding – Sexual selection • Natural selection ‒ Competition based on ability to survive to reproduce • Sexual selection – Competition based on ability to obtain many mates, or best mates • Ability to get many mates or good mates will enhance fitness regardless of other natural selection pressures • Is a special type of natural selection (mates are a type of resource) • Darwin – The Descent of Man and Selection in Relation to Sex (1871) • Outlined his theories on sexual selection and he noticed sexual dimorphism • Sexual dimorphism – different forms of individuals of different sex in the same species (peacocks males have feathers out of butt and females don’t or facial hair on humans) • Sexual selection and fitness tradeoffs • Costs and benefits ‒ Each adaptation can have a benefit (conferring higher fitness) and a cost (conferring lower fitness) ‒ fitness tradeof • Benefit outweighs the cost it is and adaptation • Natural selection example: Flippers • Bad on land • But good in water • Benefits outweigh costs • Sexual selection and natural selection are often in tension • Investment Asymmetry – Female investment in gametes and offspring generally greater than male • Sperm are cheap, eggs and offspring are expensive • (Usually) males are limited by the number of mates they can mate with (eggs they can BIO 203: Evolution Lecture 5 fertilize), females are limited by the quality of their mates and costs of offspring production • Females can mate with whomever they want to, males can mate with whomever will let them • Intrasexual competition o Combat o Mate choice • Intersexual competition o Sexual conflict o Cryptic female choice o Sperm competition
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