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3_3 Sources of genetic variability_Lecture Script.pdf

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ARCH 131
Dennis Sandgathe

UNIT 3GENETICS 33 Sources of Genetic Variability Slide 1 Title slide Slide 2 First of all before we get into this next lecture there are several more important terms for us to understandA Population in the evolutionary sense refers to a group of interbreeding organisms All members of a species can theoretically interbreed but typically only those members of a species that live within a common region have the realistic potential to interbreedthis is a populationwe often also use the term breeding Population which means the same thing but in evolutionary speak is somewhat redundantA Gene Pool refers to all the different genes and their various expressions their alleles that exist in the DNA of an entire population These are all the different traits that the offspring of members of a population have the chance of inheriting Slide 3 A Genotype is the underlying genetic makeup of an individual This can refer to their entire genome or to the alleles expressed at specific gene locations For example a pea plant may contain the alleles for green and yellow seeds and for smooth and wrinkled seedsthis is its genotypeor a portion of it anywayPhenotype is the exterior observable traits of an individual the physical expression of an individuals genotype For example even though a pea plants genotype may contain the alleles for both green and yellow seeds and for both smooth and wrinkled seeds it will only exhibit smooth yellow seeds because these are the dominant forms of these allelesthis is its phenotype We can think of Genotype as the genes of an organism and its Phenotype as what it actually looks like Slide 4 Lets now look at Sources of genetic variabilityRemember natural selection only acts on variability that already exists in the genetic makeup of individuals Here well examine where that variability comes from Although natural selection acts on the individual it is the sharing of genes between successfully reproducing individuals which results in subsequent generationstherefore the variability upon which natural selection can act realistically refers to all the genetic variability within the gene pool of a breeding population It may help to imagine all the various alleles carried by the members of a breeding population as all the available ingredients from which each individual within that group can be constructed In each subsequent generation there is a slight change in the quantities arrangement and combination of these ingredientsthe alleles Some alleles will be slightly more common and others will be slightly less common Slide 5 ndels work and from Therefore we can say based in large part on Meour current understanding of genetics that evolution is most accurately expressed as a change in allele frequency in a population from one generation to the nextThis way of looking at it provides the best clarity in trying to understand all the factors that play a role in the evolutionary process
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