Independent Assortment & Dihybrid Crosses

1. Independent Assortment & Dihybrid Crosses Mrs. Smith Biology

2. Mendel’s Questions • Mendel showed that alleles segregate during the formation of gametes but he still had one important question • Do alleles separate independently or do they stay together? • If alleles stay together: all people with blue eyes will have blonde hair

4. Mendel’s Experiment • First Mendel crossed true breeding plants with round yellow seeds (RRYY) with wrinkled green seed plants (rryy) • All F1 generation plants were hybrids • All phenotypes were round yellow seeds • All genotypes were RrYy • This cross shoed that round was dominant over wrinkled and yellow was dominant over green • This cross did not indicate whether alleles assort independently

5. Dihybrid Cross

6. Mendel’s Two Factor Cross • F1 Plants were all heterozygous • Mendel then crossed F1 RrYy to produce a F2 generation • F2 Produced 556 seeds • 315 round and yellow • 103 round and green • 103 wrinkled and green • 32 wrinkled and green • 206 had combinations of phenotypes different than eitherparent

7. Dihybrid Cross

8. Mendel’s Two Factor Cross • This clearly showed that alleles for seed shape separate independently form those for seed color • Mendel’ Experiment results were very close to the ratio predicted by a punnett square • 9:3:3:1

10. Summary of Mendel’s Principles • The inheritance of Biological characteristics is determined by individual units know as genes, passed from parent to offspring • When two or more alleles exist for a trait, some forms may be dominant and others may be recessive • In sexually reproducing organism each adult has two copies of each gene one from each parent, these genes are separated from each other when gametes are formed • The alleles for different genes usually separate independently for one another