Warm-up

1. Warm-up • If a pea plant is heterozygous for its yellow pod color, what is its genotype? • What are the odds it will pass on a trait for yellow color? • Use a Punnett square to show a cross of a heterozygous yellow-pod pea plant with a green-pod pea plant. • During what phase of meiosis do homologous pairs separate? During what phase of meiosis do sister chromatids separate? X XX X

2. Independent Segregation for 2 traits on separate chromosomes XX XX XX XX Or… X X X X X X X X How many different combinations can be made in gamete cells?

3. Two Factor Cross • Mendel crossed true-breeding plants that produce yellow round peas (YYRR) with true-breeding plants that produce green wrinkled seeds (yyrr) Parent 1 YYRR  YR YR YR YR yr YyRr YyRr YyRr YyRr Parent 2 yyrr  yr YyRr YyRr YyRr YyRr yr YyRr YyRr YyRr YyRr F1 cross produces genotype YyRr, phenotype yellow and round yr YyRr YyRr YyRr YyRr

4. Dihybrid Cross • Mendel then crosses two dihybrid plants • Remember: Monohybrid meant the organism was heterozygous for one trait (Yy) • The phenotypic ratio for a monohybrid cross is 1:2:1 • Dihybrid: Heterozygous for 2 traits (YyRr) Parent 1 YyRr  YR Yr yR yr YR YYRR YYRr YyRR YyRr Parent 2 YyRr  Yr YYRr YYrr YyRr Yyrr The phenotypic ratio for a dihybrid cross is 9:3:3:1 yR YyRR YyRr yyRR yyRr yr Yyrr yyRr yyrr YyRr

5. Let’s Practice! • EVERYONE DO THIS IN YOUR JOURNAL! • Let’s look at two traits for pea plants, flower color and plant height. • Flowers can be purple or white. Purple is dominant. What letter should we use? • P-purple, p-white • Plants can be tall or short. Tall is dominant. What letter should we use? • T-tall, t-short • We will cross dihybrid plants, what are their genotypes? What are their phenotypes? • PpTt • Purple and Tall

6. What are the possible genotype combinations for the gametes of these heterozygous plants? Parent 1 PpTt  PT Pt pT pt PpTt PT PPTT PPTt PpTT Parent 2 PpTt  Pt PPTt PPtt PpTt Pptt pT PpTT PpTt ppTT ppTt pt PpTt Pptt ppTt pptt