 Lecture: Dihybrid Crosses 

Warm-up 1.If a pea plant is heterozygous for its yellow pod color, what is its genotype? 1.What are the odds it will pass on a trait for yellow color? 2.Use a Punnett square to show a cross of a heterozygous yellow-pod pea plant with a green- pod pea plant. 3.During what phase of meiosis do homologous pairs separate? During what phase of meiosis do sister chromatids separate? X X X

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

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

Parent 1 YyRr  Parent 2 YyRr  YRYryRyRyryr yryr YYRR YYRr YyRR YyRr 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) YYRrYyRRYyRr YYrrYyRrYyrr YyRryyRRyyRr YyrryyRryyrr YR Yr yRyR The phenotypic ratio for a dihybrid cross is 9:3:3:1

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

Parent 1 PpTt  Parent 2 PpTt  What are the possible genotype combinations for the gametes of these heterozygous plants? PTPtpTpt PT Pt pT pt PPTTPPTtPpTT PpTt PPTt Pptt PpTtPptt PpTTPpTtppTTppTt PpTtppttppTt PPtt