12.2 Mendel’s Theory I. Explaining Mendel’s Results A. Alternate Versions of a Gene 1. It was thought that the traits of offspring were a blend from the parents a. ex - tall plants bred with short plants would produce medium plants b. Mendel’s results did not prove this 2. Allele – each version of a gene a. you get one allele from each parent b. The expressed allele is the dominant allele

c. The allele that is present but not expressed is recessive 1. ex – purple flowers are dominant over white flowers II. Random Segregation of Alleles A. The Law of Segregation 1. When an organism produces gametes, each pair of alleles is separated and each gamete has an equal chance of receiving either one of the alleles

III. Mendel’s Findings in Modern Terms A. Dominant alleles are written as capital letters & recessive alleles are lower case 1. ex – Purple flowers = F White flowers = f B. Genotype 1. The actual set of alleles a. ex -(Ff) C. Phenotype 1. What trait actually appears a. ex – purple flowers

D. Homozygous 1. an individual has two of the same alleles for a trait a. ex – FF or ff E. Heterozygous 1. an individual has two different alleles for a trait a. ex – Ff

IV. Mendel’s Second Experiment A. Dihybrid Cross 1. Involves two characters a. ex – seed color & seed shape B. The Law of Independent Assortment 1. During gamete formation, the alleles of each gene segregate independently C. Genes linked on chromosomes 1. Genes located close together on the same chromosome will rarely separate independently