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Week 3 Notes

by: Raquel Notetaker

Week 3 Notes BIOL 1010

Raquel Notetaker
GPA 3.5

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evolution darwinian evolution genetic drift, sexual selection, and coevolution
Introduction to Biology
Class Notes
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This 4 page Class Notes was uploaded by Raquel Notetaker on Thursday February 11, 2016. The Class Notes belongs to BIOL 1010 at Rensselaer Polytechnic Institute taught by in Spring 2016. Since its upload, it has received 24 views. For similar materials see Introduction to Biology in Biology at Rensselaer Polytechnic Institute.


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Date Created: 02/11/16
Processes that Drive Evolution:  Coevolution  Sexual selection  Genetic drift Coevolution- evolutionary arms race between species  The evolution of individuals within a population in response to selection pressure from other individuals in the population  Predator prey relationships are an excellent example o Bat and moth o Leopard and antelope The “Ghost of Predation Past” Now extinct Pleistocene predators, short-nosed bears, the dire wolf, lions, and saber toothed cars, were exceptionally fast and drove a co-evolutionary speed race with prong-horn. But they obviously lost the race Sexual Selection Charles Darwin- The Descent of Man, and selection in relation to sex Questions:  If there are costs associated with these exaggerated traits, why did they evolve?  Why do females choose males with exaggerated traits? The Peacock’s Tail Ornaments Signal Good Alleles Females Select Indicators of Good Genes  In stalk-eyes flies, females have more offspring when they chose mates with long eye stalks  In tragopans, brightness and symmetry of display are honest indicators of male health The sex lives of voles  Male montane-vole-polygamous: never settles down with one partner, lives more in isolation, gets around  Male prairie-vole-monogamous: choose female, mate 24 hours, remain with mate and become a good father helping in rearing of offspring, social but possessive Behavioral differences Studied trios of each type of vole in the field- 1 male and 2 females Slowing down the montane vole  The monogamy gene- encodes a particular type of vasopressin receptor protein where the receptor is prominently present in the brain.  Montane voles are “missing” this gene and if the gene from prairie voles is put into the montane vole, they become pair bonded and good fathers The human signal of good alleles  In voles, the length of the gene matters with the longer version of the gene indicating monogamy and parenting  The human gene comes in atleast 17 different lengths What is genetic drift? “Random changes in allele frequencies brought about by chance alone” Genetic drift in small populations  Cheetas in Africa  H*= % of loci that are heterozygous  H*= .0004 - .01  H= .067 for other large cats  Lowest of any field  70% of sperm abnormal  Sperm count < 10% of other felids  Very difficult to breed  Cheetah populations was 10-20,000  Now 1000  One or more historical “bottlenecks”  Ie. Periods in past 10,000 years when population < 100 Consequences of reduced variation  Deleterious alleles become homozygous o Similar to “inbreeding depression” o Occurs when close relatives mate  Fewer, less viable offspring  Lower survivorship  Increased chance of extinction Unpredictable genetic shifts occurring after a few individuals establish a new population are known as” Founder effects When small numbers of a larger population move to a new location (island), the genetic diversity may be lower than in the original population. Genetic drift can cause fixation of alleles and some of these may be deleterious which impacts overall fitness Hidden Assumptions of Natural Selection 1. Natural selection operates on individual variation within a population by selection a favorable individual variations and eliminating unfavorable ones- it does not act on the whole population at once 2. Nor does selection act at the species level- traits are not selected for the “good of the species”- they are selected only if they allow individuals within a population to survive and reproduce better 3. The environmental context determines whether or not a trait is beneficial and adaptive. What is beneficial in one setting may be a liability and un-adaptive in another 4. Natural selection acts on phenotypic variation, not directly on genes or genotypes. As a result of selection, both phenotypes and genotypes change since genes are the ultimate, underlying cause of phenotypic variation 5. Natural selection can act on both acquired and inheritable traits. But evolution will occur only from selection on heritable traits that are passed on to future generations


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