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