Mod. 2 Lectures 1-4
Mod. 2 Lectures 1-4 ASM 104
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This 8 page Class Notes was uploaded by Gabrielle Hsu on Friday September 4, 2015. The Class Notes belongs to ASM 104 at Arizona State University taught by Campisano in Fall 2015. Since its upload, it has received 218 views. For similar materials see Bones, Stones/Human Evolution in anthropology, evolution, sphr at Arizona State University.
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Date Created: 09/04/15
MODULE 2 LECTURE 1 INTRODUCTION This lecture focuses on specific patterns of natural selection Reminder Evolution is a genetic change in populations over time not in individuals It is a historical process Changes are heritable amp driven by processes mechanisms like meiosis amp genetic mutations that modify genetic info between generations Organisms are grouped into units usually by ability to reproduce MAIN IDEAS Species individuals that can naturally interbreed to produce fertile offspring Natural selection change in genetic frequency of certain traits in a population over time due to quotfitnessquot varying reproductive success Relies on genetic variation Fitness is not inherent but depends on the environment DNA Between related individuals amp species lots of DNA is shared but not all or there would be no variation Species that recently evolved from a common ancestor share the most DNA Ex humans amp chimpanzees share 98 of their DNA Patterns of natural selection Directional 0 Population changes in the direction of one extreme so that trait becomes more common over time Balancing o Favors the heterozygote maintaining more than one allele I In sicklecell anemia having two copies of the allele is fatal if untreated because the sickleshaped blood cells don t function correctly However the sickle cells are resistant to malaria so people with one copy are much less likely to contract it but still have 60 normal cells and often don t even know they carry the trait So in areas with a high risk of malaria the heterozygotes are more fit than either of the homozygotes as those die off from sicklecell disease or malaria Stabilizing o Selects for the average against the extremes I If human babies are too small they are less likely to survive but if they are too big there will be complications during birth possibly resulting in the mother s death Disruptive o Selects for both extremes amp against the average o Often occurs because of sudden changes in environment such as after a natural disaster 0 Example Environment has areas of black rocks amp areas of white rocks Individuals that are black or white can camou age themselves but grey ones cannot so natural selection favors the black and white CONCLUSION Natural selection can act in different ways leading to different results Directional favoring one extreme over the other Balancing favoring heterozygotes Stabilizing favoring the average over the extremes Disruptive favoring both extremes MODULE 2 LECTURE 2 INTRODUCTION This lecture is about sexual selection of which there are two types 0 Darwin discusses sexual selection in his book The Descent of Manquot referring to it as variance in the number of matesquot He began studying it after he observed characteristics of male animals such as bright colors or large feathers and wanted to know their purpose 0 Unlike natural selection which produces individuals more fit for the environment sexual selection is not necessarily related to the environment It enhances the traits that attract mates including differences between males amp females and differences between males MAIN IDEAS Intrasexual competition same sex selection malemale or femalefemale competition 0 Members of the same sex compete against each other for mates 0 The traits that allowed the winners to reproduce more are passed on 0 Example In many primates males fight each other for the opportunity to mate with females so traits such as larger body size larger canines etc that make them stronger are selected for Intersexual selection 0 Members of one sex prefer to mate with members of the other sex that have certain characteristics 0 Example Colorful fur in baboons o Runaway sexual selection Correlation is so strong that the trait becomes more amp more exaggerated eventually having a negative effect 0 Example Irish elk s antlers became larger amp larger which may have contributed to their extinction Why are males the ones with exaggerated characteristics like colorful fur feathers Difference in size of gametes Females produce large immobile gametes eggs that take a lot of effort energy to create while male gametes sperm are small mobile amp much easier to make Females invest more time in offspring amp have more to lose if they make a bad choice of mate Sexual dimorphism Difference in male and female phenotypes of the same species Driven by sexual selection Examples Differences in weight amp muscular development Fur color amp markings Anatomical features such as long canines large noses in proboscis monkeys skull shape etc Assortative mating Positive high homozygous individuals with the same alleles mate with each other Negative high heterozygous individuals with different alleles mate with each other Population parameters in humans All humans are part of the same species and are able to interbreed but mate selection is affected by other things such as geography societal amp cultural factors etc These are called breeding isolates CONCLUSION Evolution is driven by both natural selection and sexual selection Sexual selection includes both intrasexual competition amp intersexual selection and drives sexual dimorphism MODULE 2 LECTURE 3 INTRODUCTION This lecture discusses the causes amp effects of genetic mutations KEY POINTS 0 Mutations are changes in DNA sequence caused by mistakes during the copying of DNA 0 Can occur during mitosis or meiosis but only the changes during meiosis are passed down to offspring amp therefore affect evolution 0 On average about 58 out of the 32 billion nucleotides in the human genome are copied incorrectly resulting in mutations o Redundancy each amino acid has more than one codon that can code for it but each codon only codes for one specific amino acid This protects against more mutations 0 Only source of new genetic variation making evolution possible MAIN IDEAS Point mutations Change in only one base of a DNA sequence Example sickle cell anemia caused by a change in only one out of 438 bases Insertion mutations Whole portion segment of DNA copies or nucleotides inserts itself into a new region of the genome Example Huntington s disease Mutation of the HTT gene found on Chromosome 4 Normal person has 1035 repeating trinucleotides copies of CAG Person with Huntington s has 36100 CAGs Symptoms show if there are more than 40 repeats Deletion mutations Segment of DNA is missing Example Cystic fibrosis is caused by the deletion of one amino acid in the CFTR gene leading to the production of mucus that blocks airways amp glands Inversion mutation Segment of DNA is ipped amp reinserted backwards Effects of mutations Range from good protein has improved function or even a new function to bad decreased function nonfunctional or nonviable zygotes resulting in pregnancy loss but most are neutral Mutations that cause fatal diseases These diseases are usually but not always recessive amp the normal allele is dominant so an individual can be a carrier but not have the disease Examples Cystic fibrosis Huntington s disease TaySachs disease Mutations that are beneficial or improve function Sicklecell disease Lactase gene enzyme that digests milk is usually produced only during childhood but mutations can cause production to continue into adulthood SUMMARY Mutations can be retained or lost due to random drift or selection Rare in any species Can increase or decrease fitness but most are neutral Create new alleles providing the variation that drives natural selection MODULE 2 LECTURE 4 INTRODUCTION This lecture focuses on other forces of evolution such as gene ow and genetic drift KEY POINTS Microevolution changes in allele frequency within a population amp those alleles effects on the individuals of that population Gene pool all of the alleles in a population Population members of the same species that are able to interbreed Deme local population usually separated from other demes by geography that shares a gene pool amp interbreeds to produce offspring Allele frequency proportion of one specific allele in relation to all of the alleles in a population measured as a percentage out of 100 Change from one generation to the next due to natural and sexual selection Genotype frequency same as allele frequency but with genotypes MAIN IDEAS Gene ow mixing of alleles between different populations due to interbreeding Generally random Limited by geographical boundaries and by social factors in humans 0 Random gene ow where multiple populations all exchange genes with each other would result in even distribution of alleles between populations unless certain ones have a selective advantage 0 Oneway ow from larger population to smaller one o If the larger population has several alleles amp the smaller only has one that allele will be overtaken by the alleles from the larger population amp may disappear unless it has a selective advantage 0 Gene ow between neighboring populations most likely common in real life 0 Alleles are exchanged more quicklyfrequently between neighboring populations but may eventually reach other populations Clines Gradual change in allele frequency along a geographic transect high frequency in one region then gradually decreasing frequency in surrounding regions Can be caused by gene ow or by natural selection could correlate with gradually changing environment Genetic drift random changes in allele frequency over time o Founder effect Sewell Wright effect 0 Very small number of individuals genes are passed on 0 Can occur if a small group is separated from a larger population amp forms a new colony 0 Whatever allele is more common in the small group will be more common in the population they form even if it was rare in the original population 0 Examples I Mennonites small religious group that moved to Belize amp only mate with each other all have very similar appearance I Amish McKusickKaufman syndrome is very common even though it s recessive o Bottleneck effect 0 Size of a population is severely reduced by some kind of random disaster so only a few survivors can pass on their alleles 0 Extreme reduction in genetic variation SUMMARY Selection natural amp sexual Mutations point insertion deletion amp inversion Source of genetic variation Gene ow transfer of alleles between populations Genetic drift random change in allele frequency that reduces variation Founder effect amp bottleneck effect
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