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Do Now • P. 63 • What is the phenotypic and genotypic ratio when crossing a heterozygous tall plant with a homozygous recessive plant? Assume tall is dominant. Use letters and a key to depict your alleles. Use a punnett square to show work. Read • Read pages. 79-81 starting on section 4.3 • Read the drawings/illustrations as well • Task: when finished reading, you and your partner come up with a definition for independent assortment and product rule. • Do your best! P. 60 and 61 • Place both 4X4 grids on p. 60 and 61 • Follow along with video—use grid on p. 60 • And then we will do our own practice together on p. 61 • Then you will work independently on your own problem p. 62 • https://www.youtube.com/watch?v=4abO7NpP 8As Dihybrid Crosses • Dihybrid crosses - cross where the peas differ in 2 traits – A cross involving two traits – Ex. Seed color & Seed shape 5 Independent Assortment • Independent assortment – Different traits assort independently of each other • Ex. A pea plant that is RrYy, the alleles will separate and the traits will separate 6 Product Rule • The probability that events will occur simultaneously is the product of their individual probabilities. – Lets solve for pp probability • For example: the probability that an egg from the F1(Pp) will receive a p allele is ½ and the probability that a sperm from F1 (also Pp) will receive a p allele is ½ • Probability of recessive pp is ¼ ( ½ X ½ = ¼ ) Dihybrid Crosses • The First Generation – Two true breeding plants (P1) • RRYY = round yellow seed – (homozygous dominant) • rryy = wrinkled green seed – (homozygous recessive) – When they were crossed all the plants had round yellow seeds (F1) 9 Example with FOIL • RRYY x rryy - Independent Assortment • FOIL = – First First – Inner Inner – Outter Outter RY – Last Last RY RY ry RY ry ry ry 10 Example • What are the gamete possibilities with • RrYy X RRYy • Do this on your whiteboards Independent Assortment Dihybrid Cross = round yellow (RRYY) X wrinkled green (rryy) RY RY RY RY ry RrYy RrYy RrYy RrYy ry RrYy RrYy RrYy RrYy ry RrYy RrYy RrYy RrYy ry RrYy RrYy RrYy RrYy 12 Independent Assortment • The Second Generation (F2) – Self-pollinated plants from the first generation – Resulted in 9 round yellow, 3 round green, 3 wrinkled yellow, 1 wrinkled green – A ratio of 9:3:3:1 13 Independent Assortment Heterozygous round yellow seed parents = RrYy Cross = RrYy X RrYy RY Ry rY ry RY Ry rY ry RY RY RRYY RRYy RrYY RrYy Ry Ry RRYy RRyy RrYy Rryy rY rY RrYY RrYy rrYY rrYy ry ry RrYy Rryy rrYy rryy 14 Independent Assortment Heterozygous Cross = round yellow (RrYy) X round yellow (RrYy) RY Ry rY ry RY RRYY RRYy RrYY RrYy Ry RRYy RRyy RrYy Rryy rY RrYY RrYy rrYY rrYy ry RrYy Rryy rrYy rryy 15 A Summary of Mendel’s Principles • The inheritance of biological characteristics is determined by individual units known as genes. Genes are passed from parents to their offspring. • In cases in which two or more forms (alleles) of the gene for a single trait exist, some forms of the gene may be dominant and others may be recessive. • In most sexually reproducing organisms, each adult has two copies of each gene—one from each parent. These genes are segregated from each other when gametes are formed. • The alleles for different genes usually segregate independently of one another. 16 Practice • Let’s let R represent tongue-rolling, r represent a non-roller, T represent ability to taste PTC, and t represent non- tasting. Suppose a woman who is both a heterozygous tongue-roller and a non-PTCtaster marries a man who is a heterozygous tongueroller and is a homozygous PTC taster. What will their children’s phenotypes ratio be? • P. 62 Independent Assortment 18
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