1. Chapter 11.3 Mendel’s Theory of Independent Assortment AP Biology Fall 2010

2. Dihybrid Cross Dihybrids are the offspring of parents that breed true for different versions to two traits Mendel also preformed experiments involving 2 traits- a dihybrid cross A dihybrid cross is started by first crossing two true-breeding parents each exhibiting 2 forms of 2 different traits The resulting F1 hybrids were allowed to self- fertilize, giving rise to offspring of 16 different combinations

3. Dihybrid Cross Mendel correctly predicted that all F1 plants would show both of the dominant alleles ▫Example: all purple flowers and all tall plants Mendel wondered if the genes for flower colour and plant height would travel together when two F1 plants were crossed ▫What do you think?

4. Dihybrid Cross

5. The F2 results showed: ▫ 9/16 were tall and purple flowered  Both dominant forms of the trait ▫1/16 were dwarf and white flowered  Both recessive forms of the trait  As were the original parents ▫3/16 were dwarf and purple flowered  New combination ▫3/16 were tall and white flowered

6. Mendel’s Theory of Independent Assortment As meiosis ends, genes on pairs of homologous chromosomes have been sorted out for distribution into one gamete or another, independently of gene pairs of other chromosomes

7. Mendel’s Theory of Independent Assortment Most genes in most organisms follow inheritance patterns that are explained by the theory of independent assortment Although some gene pairs do not always assort independently into gametes ▫Can you take a guess about which gene pairs behave differently?

8. Review 1.What is Mendel’s theory of independent assortment? 2.What makes up a dihybrid cross? 3.Do 2 different genes travel together across generations?

9. Answers 1.Mendel’s theory of independent assortment: As meiosis ends, genes on pairs of homologous chromosomes have been sorted out for distribution into one gamete or another, independently of gene pairs of other chromosomes 2.Dihybrid cross: started by first crossing two true- breeding parents each exhibiting 2 forms of 2 different traits. The resulting F1 hybrids were allowed to self- fertilize, giving rise to offspring of 16 different combinations. 3.No, different genes do not travel together across generations. The assort independently from each other.