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Biological Sciences
BISC 110
Kevin Lam

Week 3 NotesConcept 22A Darwinian View of Life Natural Selection SummaryNatural selection is a process in which individuals that have certain heritable traits survive and reproduce at a high rate than other individuals because of those traitsOver time natural selection can increase the match between organisms and their environmentIf the environment changes or if the individuals move to a new environment natural selection may result in adaptation to new conditions evolution of new speciesConcept 23Microevolution Change in allele frequencies in population over generations three main mechanisms that can cause allele frequency to changenatural selection genetic drift chance events and gene flow transfer of allele between populations only natural selection consistently improves the match between organisms and their environment adaptationConcept 231Genetic VariationGenetic variation Differences among individuals in the composition of their genes or other DNA segmentsGenetic variation makes evolution possible variation in heritable traits is a prerequisite for evolutionPhenotype is the product of an inherited genotype and many environmental influencesVariation within a PopulationCharacters that vary within a population may be discrete or quantitativeDiscrete characters are determined by single gene locus with different alleles that produce distinct phenotypesMost heritable variation involved quantitative characters which vary along a continuum within populationHeritable quantitative variation usually results from influence of two or more genes on single phenotypic characterMeasure genetic variation at wholegene level gene variability and at molecular level of DNA nucleotide variationHeterozygous individual has 2 different alleles for given locus homozygous individual has two identical alleles for that locusExample On average the fruit fly Drosophila melanogaster is heterozygous for about 1920 or its 13700 loci 14 and homozygous for all the rest Therefore it has an average herterozygosity of 14When determining gene variation how do scientists identify heterozygous lociSurvey proteinproducts of genes using gel electrophoresis measure nucleotide variation biologists compare DNA sequences of two individuals in population and then average the dataVariation between PopulationsGeographic variation Differences in the genetic composition of separate populationsCline A graded change in a character along a geographic axis
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