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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
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Independent Segregation for 2 traits on separate chromosomes
XX XX Or… X X X X How many different combinations can be made in gamete cells?
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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
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Dihybrid Cross Mendel then crosses two dihybrid plants Parent 1 YyRr
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
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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
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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
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