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by: Lydia Trick

BIOL1082 BIOL 1082

Lydia Trick
GPA 3.5

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Week 3 Notes
Biology II
Dr. Beyette
Class Notes
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This 7 page Class Notes was uploaded by Lydia Trick on Tuesday August 30, 2016. The Class Notes belongs to BIOL 1082 at University of Cincinnati taught by Dr. Beyette in Fall 2016. Since its upload, it has received 9 views. For similar materials see Biology II in Science at University of Cincinnati.


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Date Created: 08/30/16
Biology 8/24 ● Homology: similar structures from a common ancestor with a similar function but best suited with different functions for the individual animal; diverged over time ● analogous : similar function but not homologous ● Insects wings are analogous to birds and bats ○ Adapted through similar environments [convergence] ○ [Fins in sharks and mammals] ● Divergent, convergent, parallel evolution ● Vestigial structures: from an ancestor that are not needed but still remain in or on the body ○ Appendix, erector pili and hair, wisdom teeth, tailbone ● Time is a requirement of evolution ● Convergent: selective pressures from common environments to push different groups of animals to evolve similarly ○ [Phenotypic similarity between marsupials and placental mammals] ● We lost our tail because we are more bipedal ● Hominids: group more closely related to humans than chimps From 23.1 and 23.2 ● Microevolution is the change in allele frequencies in a population through generations ● 3 mechanisms that can cause allele frequency change: genetic drift, natural selection, gene flow ● Only natural selection consistently improves the match between organisms and their environment ● Considerable genetic variation can also be measured at the molecular level of DNA (nucleotide variability) - little of this results in phenotypic variation ● Crossing over in meiosis, slippage in DNA replication, and activities of transposable elements are a potential source of variation ● Gene duplication of large segments on chromosomes may be harmful, but duplication of smaller segments can be beneficial [olfactory receptor genes] ● Individuals in a population must differ genetically for evolution to occur 8/26 ● Microevolution: genetic variation of alleles [genetic level] ● Evolution can’t happen without raw materials, and without variation in a population ● Eastern Africa has a lot of genetic diversity because it is where humans first evolved ● Hardy-W equilibrium - suggests a population is not evolving and the allele frequencies are constant From 23.4 ● Barnacle obtaining more food and therefor being able to produce more offspring is an example of how in a given environment, certain traits can lead to greater relative fitness ● Selection acts more directly on the phenotype than on the genotype; it acts on the genotype indirectly, via how the genotype affects the phenotype ● Directional, disruptive, and stabilizing selection ○ Natural selection can alter the frequency distribution of heritable traits in these three ways, depending on which phenotypes in a population are favored ● Balancing selection ■ Genetic variation is often found at loci affected by selection ■ Recessive alleles persist because they are hidden from selection when in heterozygous individuals ○ Heterozygote advantage ■ This is defined in terms of genotype, not phenotype ● Why natural selection cannot fashion perfect organisms ○ Selection can act only on existing variations ○ Evolution is limited by historical constraints ○ Adaptations are often compromises ○ Chance, natural selection, and the environment interact 8/29 ● Rate of a survival of a species is not fitness, which is more about a population MasteringBiology due 8/26 ● The original source of all genetic variation is ○ Mutation - the raw material for evolution ● How does diploidy help preserve genetic variation? ○ It allows recessive alleles that may not be favored in the current environment to be preserved in the gene pool by propagation [reproduction or spreading] in heterozygotes ○ {natural selection tends to decrease genetic variation. recessive alleles are shielded from natural selection in heterozygotes} ● The best modern definition of evolution ○ Descent with modification ● What is true about variation? ○ All new alleles are the result of nucleotide variability ○ Not all genetic variation produces phenotypic variation and vice versa** ● Genetic variation must ○ Be present in a population before natural selection can occur ● According to Hardy-Weinberg theorem, the frequencies of alleles in a population will remain constant if _____ is the only process that affects the gene pool ○ Sexual selection ○ Sexual reproduction does not affect the frequencies of alleles in a gene pool ● For a biologist studying a small fish population in a lab, which Hardy- Weinberg condition is the easiest to be met? ○ No gene flow ● What are basic components of Hardy-Weinberg’s model? ○ Frequencies of 2 alleles in a gene pool before and after random mating ○ Hardy and Weinberg were trying to determine how and whether allele frequencies in a population change from one generation to the next ● Genotype frequencies in the offspring generation must add up to 1 ● The 5 assumptions of the Hardy-Weinberg model: ○ No selection at the gene in question, no gene flow, no genetic drift, no random mating, no mutation ● What evolutionary force constantly results in adaptive changes in allele frequencies? ○ Selection ○ Mutation without selection and genetic drift are random processes that may lead to adaptive, maladaptive, or neutral effects on populations** ● What evolutionary force could result in new genetic information in a population? ○ Mutation ○ Mutations are changes in a cell’s DNA, and can introduce new genetic information in the next generation MasteringBiology due 8/29 ● The evolutionary effects of genetic drift are greatest when ○ The population size is small ○ Changes in the gene pool of a small population are frequently due to genetic drift ● What explains the occasional high frequency of certain inherited disorders among human populations established by a small population? ○ Founder effect ○ The founder effect is genetic drift attributable to colonization by a limited number of individuals from a parent population ● In evolutionary terms, an organism’s fitness is due to its ○ Contribution to the gene pool of the next generation ● Blue poppies native to China were grown at a plant-breeding center in California. The plants with the thickest leaves were most likely to survive and reproduce in the drier climate. After several generations, the percentage of thick-leaved plants had increased by 42%. This adaptation of the poppies to their new environment is due to ○ Directional selection ○ Their characteristics shifted in response to their environment ● What is the only evolutionary mechanism that leads to adaptive evolution? ○ Selection ○ Because natural selection has a sorting effect, it consistently increases the frequency of alleles that improve the match between an organism and its environment From 24.1 and 24.2 ● Ongoing exchange of alleles from gene flow [transfer of alleles between populations] tends to hold the populations together genetically ○ Absence of gene flow is important in the formation of new species** ● Reproductive isolation {barriers} block gene flow between species and limit the formation of hybrids ● Allopatric - “other country” ● Sympatric - “same country” ● A species may originate from an accident during cell division that results in an extra sets of chromosomes - polyploidy ○ A tetraploid can produce fertile tetraploid offspring by self-pollinating or by mating with other tetraploids ● In one generation, one autoploidy can generate reproductive isolation without any geographic separation ● Most hybrids are infertile because the set of chromosomes from one species cannot pair during meiosis with the set of chromosomes from the other species ○ However, an infertile hybrid may be able to propagate [spread] itself asexually MasteringBiology due 8/31 ● What is the most important factor that holds the gene pool of a species together and prevents speciation? ○ Gene flow ○ Gene flow refers to the transfer of alleles between populations ■ As long as populations have gene flow and are exchanging alleles, speciation is unlikely ● Example of temporal isolation ○ One animal nocturnal, other is dinural they breed at different time and their gametes cannot mix ● The first step in allopatric isolation ○ Geographic isolation ● 2 populations of crickets have different songs, what mechanism prevent them from interbreeding if they come in contact? ○ Behavioral reproductive isolating mechanism ● Sympatric speciation is ____ ○ The appearance of a new species in the same area as the parent species ■ This is due to a radical change in the genome*** ● What causes speciation most rapidly? ○ Autoploidy ○ Has been known to show nearly instantaneous speciation in plants ● How are 2 different species most likely to evolve from an ancestral species? ○ Allopatrically, after the ancestral species has split into 2 populations ● Order of events in allopatric speciation ○ Genetic isolation, genetic drift, divergence 9/2 ● The mating call of the Bombina frog hybrids will become stronger than the parents’ populations through natural selection to reinforce reproductive isolation ○ Female being attracted to their own male species calls ● Gene flow decreases chances of speciation ● Hybridization re establishes some gene flow ● Natural selection selects against hybrid traits such as mating calls and colors ● Adaptive radiation is common on archipelago ○ Because of dispersal in new niches ● 2 kinds of speciation ○ Morphological ○ Punctual equilibrium Aug 24 Powerpoint ● Shared characteristics between humans and other mammals ○ Nail beds, hair, mammary glands, four-chambered heart ● Hominoidea ○ Loss of tail, dorsally oriented scapula, more upright, more bipedal, larger brain, reduced canines, reduced sexual dimorphism, loss of opposable thumb on foot ○ Gibbons, orangutans, chimps, gorillas, hominins ● Cultural innovation does not eliminate natural selection in humans, rather it creates new selection pressures ○ Lactose intolerance, adaptations to malaria infection ○ We continue to adapt both culturally and genetically to a changing world ● Africans have the most genetic diversity ○ This is where they have been evolving the longest ● Mammals originally evolved in land [evidence in fossils] so ancestors of whales must have taken to the water at some point ● Majority of vertebrates are fish ● Evolution in action ~ transitional forms ○ Archaeopteryx ● Neural crest is unique to vertebrates, which is why it is thought that we have distinct heads and faces ● Microevolution - drug resistance ● Macroevolution is harder to observe in action Aug 26 Powerpoint ● Conditions always true of populations evolving due to natural selection? ○ 1. Populations must vary in traits that are heritable ○ 2. Some heritable traits must increase reproductive success ● The gene pool includes ○ All of the alleles in a population ● In a small population, some chance reason may an allele to not reproduce successfully and the frequency will change, as it would within a genetic drift or bottleneck event ● Assortative mating does not alter allelic frequencies, but it results in fewer heterozygous individuals as you would expect in a population undergoing random mating ● Mutations show more quickly in small populations ● Natural selection favors traits that increase fitness ● Both natural and sexual selection are non-random processes ● HbS carriers have been naturally selected because the trait confers some resistance to malaria ● Sometimes, a restriction in genetic variability is imposed on populations by natural disasters. The surviving individuals reflect only a small, random genetic sample of the population affected. This process is ○ Bottleneck effect ● Females prefer to mate males of a rarer color. This is ○ Frequency-dependent selection ● Heterozygote advantage ○ Keeps both alleles in the population ● Extinction of a large population leaving behind a small, distant subpopulation ○ An example of allopatric speciation ● Cichlids ○ Rapid adaptive radiation [common on archipelago] to fill in empty niches with different food sources ○ Alternative splicing of mRNA ○ Adaptive radiation in Galapagos finches ● Reproductively isolated group of similar organisms ○ Biological species concept ● F ● F ● F ● f


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