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Week 3 Notes

by: Chasia Notetaker

Week 3 Notes BIOL 12000

Chasia Notetaker
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These notes cover all material from the week of February 8th
Fundamentals of Biology II: Ecology and E
Nancy L Jacobson
Class Notes
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This 4 page Class Notes was uploaded by Chasia Notetaker on Saturday February 6, 2016. The Class Notes belongs to BIOL 12000 at Ithaca College taught by Nancy L Jacobson in Fall 2016. Since its upload, it has received 27 views. For similar materials see Fundamentals of Biology II: Ecology and E in Biology at Ithaca College.


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Date Created: 02/06/16
Notes for the Week of February 8, 2016   Genetic Drift & Natural Selection Genetic drift­ chance events causing changes in allele frequency of a population a.    ­random fluctuation (especially in small populations) b.   ­bottle neck                             i.   ­the population is reduced within its original range 1.   ­allele frequencies change due to sampling error 2.   ­can lead to loss of alleles and therefore a loss of genetic diversity in the population c.    –founder effect                             i.   When small sample of original population starts a new population 1.   Allele frequency changes due to sampling error 2.   Leads to loss of alleles and genetic diversity 3.   Can lead to a greater frequency of an allele than in the source population Natural Selection ­some individuals produce more offspring (that live to reproduce) than do others because certain  features of their phenotypes give them an advantage          ­so an individual’s survival only matters in terms of how many offspring it produces ­the phenotype that has an advantage depends on the environment (biological and physical)   Variation of Skin Color ­caused by multiple genes          ­dominant alleles of more than one gene cause melanin to be made and deposited in the  skin          ­melanin blocks UV light Effects of UV on the Skin ­skin cancer          ­usually occurs later in life, often after reproduction has finished ­breakdown of folate (folic acid)          ­folate is a vitamin needed for fetal neural tube development and spermatogenesis ­Synthesis of vitamin D          ­needed for proper bone development in fetus and children 13.2  > The Study of Fossils Provides Strong Evidence for Evolution Fossils­imprints or remains of organisms that lived in the past ­document between past and present organisms and the fact that many species  have become extinct ­usually bones and teeth of vertebrates and shells ­rarely, an entire organism, including soft parts are preserved in a medium ­insects in amber ­mammoths, bison, even prehistoric humans frozen in ice or preserved in bogs Strata­ sedimentary rock covered and compressed by older layer Paleontologists­ scientists who study fossils Fossil record­chronicle of evolution over millions of years of geologic time engraved in the order in which fossils appear in rock strata 13.6  >Darwin Proposed Natural Selection as the Mechanism of Evolution Artificial selection­ selective breeding of domesticated plants and animals to promote the  occurrence of desirable traits in offspring ­there are two essential components ­variation among individuals allows the breeder to select the animals or plants  with the most desirable combination of characters as breeding stock for the next generation ­heritability is the transmission of a trait from parent to offspring ­the essence of natural selection is unequal reproduction ­having more babies than the environment can handlec Evolution through Natural Selection 1. Individuals do not evolve, population do over time as adaptive traits become more common in the group and other traits change or disappear  2. Natural Selection can only amplify or diminish heritable traits 3. Evolution is not goal directed, it does not lead to perfectly adapted organisms Natural selection leading to adaptive evolution can be quantified ­a fitness value of 1 is assigned to the phenotype with the highest representation ­all other phenotypes are assigned based on their reproductive success relative to the dominant  types ­adaptations are not always perfect 13.13    >Natural Selection is the only Mechanism that Consistently Leads to Adaptive Evolution ­genetic flow, gene flow, and mutation can lead to microevolution  ­only by chance can they improve a population’s fit to its environment ­the process of natural selection, that better adapted individuals are more likely to survive and  reproduce, is not random ­only natural selection leads to adaptive evolution Adaptive evolution­evolution that results in a better fit between organisms and their environment ­by consistently favoring some alleles over others, natural selection  improves match between organism and environment ­however, environment may change making adaptive evolution a  continuous dynamic process ­natural selection is usually thought of as “survival of the fittest” however it is better thought of  as greater relative fitness ­the contribution of an individual makes to the gene pool of the next generation relative  to the contribution of other individuals  13.14  >Natural Selection can alter Variation in a Population in three ways Stabilizing selection­ favors intermediate phenotypes Directional selection­ shifts over all makeup if the population against individuals at one end of  the phenotypic extremes ­most common during periods of environmental change or when members of a species  migrate to a new habitat with different environmental conditions Disruptive selection­ when environmental conditions vary in a way that favors individuals at  both ends of a phenotypic range over individuals of the intermediate range 13.17  >Diploidy and Balancing Selection Preserve Genetic Variation ­in a heterozygote, a recessive allele is “protected” from natural selection ­”hiding” recessive alleles can maintain a huge pool of alleles that may not be favored but could  be advantageous if the environment changes     ­genetic variation is preserved rather than reduced by natural selection Balancing selection­ when natural selection maintains stable frequency of two or more  phenotypic forms in a population Heterozygote advantage­ heterozygous individuals have greater reproductive success than either  homozygotes ­results in two or more alleles for a gene being maintained in a population Frequency dependent selection­ maintains two different phenotypic forms in a population ­natural selection acts against either trait if it becomes too common 13.18    > Natural Selection cannot Fashion Perfect Organisms selection can only act on existing variation ­natural selection favors from what is available ­new, advantageous alleles do not arise on demand evolution is limited by historical constraints ­each species has a legacy of descent with modification from ancestral forms  ­evolution uses existing structures and adapts them to new situations  adaptation are often compromises chance, natural selection, and the environment interact ­chace events often affect the genetic makeup of the population ­genetic drift can result in a loss of beneficial alleles ­the environment may change unpredictably, limiting adaptive evolution’s ability to  match organism and evironment


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