# Each with a 16 chance so the probability is 136 136

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each with a 1/6 chance so the probability is 1/36 +1/36 +1/36 +1/36 +1/36 +1/36 = 1/6oProbability in Mendel’s crossesoSame rules apply to Mendel’s studiesEx. purple and white flowers. Crossing heterozygotes ¼ pp, ¼ PP, ½ PpWe get this by the product ruleoThen, if we want to know the probability of obtaining a purple flower, the rule ofaddition applies because 2 different genotypes make the purple phenotype¼ PP + ½ Pp = ¾ of the F2 are expected to have purple flowersototal probabilities must add up to 1 –the remaining ¼ of offspring are expected to have white flowers. Ratio 3:1, close to that which Mendel obtainedEoMendeloTestcross to check validity of his hypothesesRealized he could assess validity by determining if they could successfully predict the outcome of a different type. He crossed purple Pp x pp, both with a probability of ½ - thus phenotypes expected to be 1:1 ratioMendel’s ratio closely matched and also achieved the same 1:1 ratio with other traitsoA cross between individuals with a dominant phenotype and homozygous recessive individual is called a testcross. Genetics use a testcross to determine whether an individual with a dominant phenotype is homozygous or heterozygous. If offspring show a 1:1 ratio, then the organism was heterozygous. If all are showing the dominant phenotype, then the organism was homozygous dominantoThis is impractical with humans.
LECTURE 12 PREP18.1Variation in natural populationsoPhenotypic variation differences in appearance or function among individuals of a population oIf a difference is heritable it is passed on from generation to generation17
APhenotypic variationoMircoevolution studies often begin assessing these phenotypic variationsoMost characters exhibit quantitative variation: individuals differ in small incremental waysoVariation that is measured on a continuum (i.e. height) rather than discrete units/categoriesoUsually data on quantitative variation is put on a bar graph or curve if there is sufficient dataoThe width of the curve is proportional to variability among individualsBroad, low curve indicates a lot of variationHigh narrow curve indicates little variationoMean describes the average value of a character or its variability within populationsoNatural selection often changes mean value of a character or its variability within populationsoCharacters that Mendel studied were qualitative – they exist in two or more discrete states and intermediate forms are often absentoEx. snow geese have blue or white feathersoExistence of discrete variants of a character is called polymorphismoSuch traits are polymorphici.e. Scottish snailsoBiochemical polymorphisms like human A, B, AB and O blood types are also common.oWe describe phenotypic polymorphisms quantitatively by calculating percentage of frequency of each traitoPhenotypic variation can be caused by genetic differences but also environmental factorsand interactionoResult: genetic and phenotypic variations may not be perfectly correlatedo