ZOL 141 1st Edition Lecture 10 Outline of Last Lecture I Gregor Johann Mendel A Study of single traits B Experimental setup C Conclusions D Mendel s first law Outline of Current Lecture I Experimental Setup II Experiments and Results III Branch Diagram a Probability Rules IV Probability Current Lecture Transmission of Genes from Generation to Generation Part Two Question addressed does the inheritance of one characteristic affect the inheritance of a different characteristic Experimental Setup From previous crosses with peas o Smooth is dominant to wrinkled o Yellow is dominant to green Symbols o Seed shape S smooth s wrinkled o Seed color Y yellow y green Experiments and Results Smooth yellow x wrinkled green o all smooth yellow Dihybrid crossed smooth yellow x smooth yellow o 9 16 smooth yellow 3 16 wrinkled yellow 3 16 smooth green 1 16 wrinkled green o 9 3 3 1 both parental phenotypes appeared two new phenotypes o traits are not linked together conclusion o alleles of one gene pair assort into gametes independently of alleles belonging to other gene pairs o principle of independent assortment Mendel s second law Mendel looked at all traits individually seed shape seed color Determining types of gametes Pea plant has genotype SsYy What types of gametes can this plant produce o Each gamete has to receive one copy of each gene o Equal chance that either allele is included in the gamete o Number of gametes is 2 n n the number of heterozygous traits Branch Diagram Use probability to consider the inheritance of multiple traits simultaneously by combining the individual probabilities of each trait Probability o Rule 1 Product rule the probability of independent events occurring together is the product of the probabilities of the individual events Two dice what is probability of rolling a four and a five 1 6 x 1 6 so probability of rolling a four with the first AND a five with the second 1 36 o Rule 2 Sum rule the probability of either of two mutually exclusice events occurring is the sum of their individual probabilities One die what is probability of rolling a four OR a five 1 6 1 6 2 6 or 1 3 steps for branch diagram genotype o 1 Visualize the dihybrid cross as two monohybrid crosses o 2 List probability of genotype for one trait o 3 List probability of each genotype for the second trait next to each of the genotypes for the first trait o 4 Follow each branch and multiply probabilities product rule Steps for branch diagram phenotype o 1 Visualize dihybrid cross as two monohybrid o 2 listprob of each phenotype for one trait o 3 listprob of each phenotype for the second trait next to each of the phenotypes for the first trait o 4 follow each branch and multiply probabilities Probability four traits what is prob of having genotype AaBBccDd o i e Aa and BB and cc and Dd o Aa 1 2 and BB 1 4 and cc 1 4 and Dd 1 2 o So x x 1 4 x 1 2