evolution continued BIO 152
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This 4 page Class Notes was uploaded by Samuel Croteau on Monday April 11, 2016. The Class Notes belongs to BIO 152 at Massachusetts College of Pharmacy & Health Sciences taught by Dr. Demasi in Fall 2016. Since its upload, it has received 14 views. For similar materials see Biology of the organism in Biology at Massachusetts College of Pharmacy & Health Sciences.
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Date Created: 04/11/16
Microevolution • There are five conditions that all must be met to have no evolution ◦ No mutations ◦ Random mating ◦ No natural selection ◦ Extremely large population size ◦ No gene flow Genetic Varation • Formation of new alleles by ◦ Change in DNA sequence ◦ B allele originated from the b allele + a mutation ◦ Mistakes copying DNA ◦ Point mutations, insertions, deletions- tiny changes (new alleles) • Altering gene number ◦ Duplicate genes and mutations – brand new genes • Rapid reproduction ◦ viruses, bacteria – reproduce faster.....they evolve faster.... • Sexual reproduction ◦ Crossing over at meiosis I ◦ Independent assortment during meiosis ◦ Fertilization ◦ Mutations in egg and sperm Microevolution • Change in allele frequencies in the gene pool of a population over time ◦ Genetic Drift occurs only a few reproduce more genetic differentiation occurs • Bottleneck effect ◦ Sudden reduction in population size due to change in environment (storm, drought) • Example ◦ Micronesia (Island nation in Pacific) ◦ 1775- Typhoon kills 90% of population ◦ One survivor had a rare genetic eye condition ◦ Now % of the population has it • Founder effect ◦ A few individuals are isolated from larger population ◦ Allele frequencies in the founder population spread • Example ◦ High number of deaf people born on Martha's Vineyard ◦ Early settler had a rare genetic deafness disorder Speciation (Chp24) • Microevolution + Reproductive Isolation = a new species (Speciation) • Speciation ◦ the origin of new species • What is a species? ◦ A population that can interbreed and produce viable, fertile, offspring ◦ They can't/won't breed with other population • Examples ◦ Rhagoletis pomonella – North America maggot fly ◦ Normally mates and lay eggs in hawthorn fruit ◦ 1800s – apple trees introduced by Europeans • Gene pools start to separate ◦ Apple-preferring flies mate with other apple preferring flies ◦ Haw-preferring flies mate with other haw-preferring flies • Apple trees give fruit earlier than hawthorn trees ◦ Apple-preferring flies develop earlier in the season • 200 years later neither apple flies or hawthorn flies can't wont don't mate with each other Apple flies and hawthorn flies are different species Reproductive isolation • Barriers that prevent two species from mating and/or producing viable, fertile offspring • Pre-zygotic barriers ◦ Habitat Isolation ◦ Temporal Isolation ◦ Behavioral Isolation ◦ Mechanical Isolation ◦ Gametic Isolation • Post-zygotic barriers – offspring is a hybrid ◦ Reduced Hybrid Viability ◦ Reduced Hybrid Fertility (Donkey + Horse = Mule) ◦ Hybrid breakdown Speciation • Live in different habitats Habitat isolation • Mate at different times a year Temporal isolation • Mating rituals are different Behavioral isolation • Apple flies and hawthorn flies becoming different species ◦ Gene flow is not occurring between these population ◦ Example Apple-preferring flies develop and reproduce earlier in year. How does speciation occur? • Two main modes of speciation • Allopatric speciation ◦ population divided geographically – isolated subpopulations ◦ They evolve separately (VISTA) ▪ Different predators, food source, etc in new enviorment • Sympatric sepciation ◦ populations live together, but reproductive barriers form. ▪ Habitat differentiation – appearance of new habitat or food source ▪ Sexual selection – females develop preference Speciation • Fossil evidence -punctuated or gradually ◦ Depends on the genes/mutations – major or minor genetic variation ◦ Average of 6.5 million tears (4,000 years to 40 million years) • Species- A population that can interbreed and produce viable, fertile offspring • Reproductive isolation ◦ No gene flow between two different species ◦ barriers to reproduction • Example ◦ Evolution of dogs ▪ Began about 50,000 years ago with wolves ▪ Humans did the selection (artificial selection) ▪ VISTA ▪ compare dog vs wolf ( bones, physiology, DNA) • Examples Now ◦ Russian silver fox experiment ▪ Silver foxes bred in captivit for their fur ▪ Foxes are aggressive, and scared of people ▪ 1959 – breed (selected) foxes for tameness ▪ Over time you now can go up to the foxes and pet them • They selected for one trait – which 'revealed' new traits ◦ In natural section selecting for one trait could lead to new traits ▪ Species become different ▪ Reproductive barriers could exist ▪ Habitat isolation ▪ Temporal isolation ▪ Behavioral isolation ▪ Mechanical isolation ▪ Gametic isolation ▪ Reduced Hybrid Viability ▪ Reduced Hybrid Fertility ▪ Gene pools have separated
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