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Wednesday – September 23, 2009 Objectives: SWBAT create and analyze Punnett Squares. Catalyst: What is the difference between a gene and an allele? How do we represent dominant alleles? Recessive alleles? Agenda Catalyst Review Making Babies Lab (GASP!) Punnett Squares Guided Practice Independent Practice Closing Catalyst A gene codes for a trait- eye color, ear lobes, dimples, etc. An allele is a different version of a gene. Ex: Brown vs. Blue eyes Ex: Attached vs. Free hanging earlobes Ex: Dimples vs. No dimples Review Yesterday’s Vocab Traits Allele Homozygous Heterozygous Dominant Recessive Check your awesome notes! Remember… GENOTYPE = combination of alleles inherited from the parents (the genes) PHENOTYPE = physical expression of the trait Today, you are going to have 20 kids. What? Yes. In 15 minutes, you will have 20 kids. You will need to find someone in the class to mate with. We will demonstrate how this works. Key Point #1 Punnett Squares are diagrams that are used to predict the genotypes of offspring. Probability…not EXACT It is important to note that Punnett Squares only give probabilities for genotypes It doesn’t give you the EXACT outcomes You will see when we start creating our Punnett Squares Key Point #2 You can never know for sure what offspring will look like, you can only predict based on probability. Key Point #3 We refer to the parent generation as P1 and the offspring of that generation as F1. P1 F1 Before we get started… CAPTIALIZED letters are DOMINANT lowercase letters are recessive Examples: B = brown hair (DOMINANT) b = blonde hair (recessive) Y = yellow (DOMINANT) y = green (recessive) P = purple (DOMINANT) p = white (recessive) Before we get started… D = dimples d = no dimples Homozygous dominant Homozygous recessive Genotype: DD Genotype: dd Phenotype: have dimples Phenotype: no dimples Heterozygous Genotype: Dd Phenotype: have dimples Before we get started… B = brown eyes b = blue eyes Homozygous dominant Homozygous recessive Genotype: BB Genotype: bb Phenotype: brown eyes Phenotype: blue eyes Heterozygous Genotype: Bb Phenotype: brown eyes Big Pun-nett Let’s make our own. First things first, draw yourself box and split it into 4 squares. Punnett like its Hot Now, read the problem and find the parents’ genotypes. *Remember, use the first letter of the dominant trait. BB A homozygous dominant brown eyed male mates with a blue eyed female. bb Punnett Squares are COOL Parents go on the top and on the left (keep them together) It doesn’t matter which parents goes on the top or the left B B b b b b Punnett Square Dance Now, bring em together. The four boxes represent the possible kids. B b b B Bb Bb Bb Bb Just Punnett! Now, we analyze. Use quarters to figure out percentages. B •How many homozygous dominant do we have? 0% •How many heterozygous do we have? 100% •How many homozygous recessive do we have? 0% b b B Bb Bb Bb Bb Punnett baby one more time Lastly, figure out percentages by phenotypes. •What percentage will have brown eyes? 100% •What percentage will have blue eyes? 0% B b b B Bb Bb Bb Bb Let’s do one more on the board A heterozygous dimpled male mates with a heterozygous dimpled female. Whiteboard Guided Practice: Seed Shape R R R RR RR r Rr Rr R = round r = wrinkled Solve the following Punnett Square. A homozygous dominant round seeded plant is crossed with a heterozygous wrinkled plant. Find the genotype and phenotype probabilities. Guided Practice: Earlobes F f f Ff ff f Ff ff F = free f = attached Solve the following Punnett Square A male with attached earlobes mates with a heterozygous free hanging earlobe female. Find the genotype and phenotype percentages. Oh, how we love Spongebob! Your teacher will now pass out the GP & IP “Punnett Squares – Spongebob Style” worksheets We’ll do some of them together…then you get to try the rest on your own! Wrap Up Punnett Squares are diagrams that are used to predict the genotypes of offspring. You can never know for sure what offspring will look like, you can only predict based on probability. We refer to the parent generation as P1 and the offspring of that generation as F1. Exit Question Create a Punnett Square. Do a cross of two heterozyous parents for brown eyes. List the genotypes & phenotypes probabilities of both the P1 and F1 generations.
