BSC 315 Lecture Notes - Lecture 2: Punnett Square, Genotype, Gamete
15 Jan 2017
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When was mendel"s theory proven: theories are never proven. The two alleles of a gene segregate from each other during gamete formation, and unite at random at fertilization, restoring the diploid chromosome number. The team law is applied arbitrarily and informally. A simple method to portray a cross (post-mendel): x and y axes contain the gametes, each box is a fertilization event. Mating to heterozygotes produces: 3:1 phenotypic ratio (yellow:green, 1:2:1 genotypic ratio (yy:yy:yy) Prediction: the yellow f2s contain both yy and yy in a 1:2 ratio. Test: determine the genotype of yellow f2s: test cross: cross to determine the genotype of an unknown individual, procedure: unknown x homozygous recessive (homozygous recessive = tester strain) Yellow f2s have two different genotypes, yy and yy, abbreviated as y- : ( - = unknown allele, either y or y_ Predict progeny if y- is actually: yy yy x yy 100% yellow, yy yy x yy 50% yellow (yy) and 50% green (yy)
