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BASIC GENETICS SUMMARY.pdf

34 Pages
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Department
Biology (Sci)
Course Code
BIOL 202
Professor
H E N D R Y...

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Description
BASIC GENETICS SUMMARY Hendry Quantitative genetics - Polygenic: traits influenced by multiple genes - Influenced by environmental conditions - Leads to continuous variation in the trait - Examples o Heights of cadets o Swimming speed of men/women o General cognitive ability (SATs, IQ tests) - Increase # loci = more continuous variation - Environment causes phenotype to vary with genotype (even with one locus) - Variance SS ( ) = = N # Total phenotypic variance = Genetic (AID) + Environmental(ME) - Additive genetic variance o Variance due to additive effects of alleles & genes o Hybrids = intermediates o Resemblance o Hybrid backcrosses to parent forms = phenotypes proportional to the amount of genome in group - Dominance variance o Variance due to dominance effects between alleles o Hybrid = dominant phenotype - Epistatic variance o Due to interactions between different loci o Possible deviation from additive & dominance o Example: Soap berry bug Derived Golden rain tree Smaller beak Ancestral Balloon vine fruit Longer beak Beak type = additive, dominance & epistasis Preference to host site = additive - Maternal o Variance due to phenotype of mom o Important in natural population o Types Genetic Plastic o Example: Mosquito fish weights - Stickleback o Additive genetic effects o Dominance genetic effects Backcross shows: gill rakers = additive & body depth = dominance) Body depth: Length Gill rakers Lake Bigger More Stream Smaller Less - Heritability o Broad sense Proportion of phenotypic variance that has a genetic bases = o Narrow sense Proportion of the phenotypic variance that has additive genetic variance = resemblance between parents & offspring = - Estimating heritability methods o Resemblance between sibs o Resemblance between twins o Slope parent/offspring regressions o Cross-fostering to remove maternal effects (Ex: song sparrow) - Types of selection o Directional Mean shifts Variance changes Evolutionary response (R) = change in mean trait value from one generation to the next Selection differential (S) = difference in mean trait value from before to after selection but before reproduction = o Stabilizing Hybrids = fittest Variance changes Example: increase # galls decrease bugs increase bird attacks o Disruptive Extreme phenotype = fittest Variance changes Example: beak morphs in Galapacos islands - Alternative formulae = = = = , = = - Correlations between traits o Phenotypic correlations Direct selection on 1 indirect selection on 2 Example: arm & leg o Genetic correlations Selection on 1 evolutionary change in 2 Measure not only A but additive genetic covariances between traits + 1 = 1 + 2 - Regression charts o Selection gradients (Survivals & deaths) o V & A basA on parent/offspring relationship o Predictions using = o Measure evolutionary responses o Comparisons between observed & predicted evolutionary response - Gene flow o Draws phenotypes closer together o Even when low = substantial effects on adaptive divergence o Example: stickleback Lake Outlet Inlet Outlet fish phenotypically closer to lake then inlet o Gene flow increases = decrease adaptive divergence Chevrette Genome Composition - Chromosome o Telomere o Kinetochore o Centromere o Sister chromatids o p=short arm o q=long larm - C-value = DNA content of an organism o C-value paradox: no correlation between evolution & genome size increase transposons = increase genome size & repetitive sequences - Classes of eukaryotic DNA sequences Copies/Genome Average bp Where Single copy DNA 1-10 800-1200 Structural genes Moderately 10-100 000 300 rRNA genes repetitive Ribosomal proteins Transposons Highly repetitive > 100 000 Satellite & non-satellite DNAs - Satellite DNA o Prokaryotes = single band for given density on CsCl gradient o Eukaryotes =2 bands (Main band & satellite band (repetiti
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