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The Principles of Genetics 1. In corn plants, rough seed shape (R) is dominant over smooth seed shape (r) and yellow seeds (Y) are dominant over white seeds (y). Determine the probable seed shape and color of the F1 generation of offspring whose parents are heterozygous for the traits be completing the Punnett square below. P1 generation RY RrYy x Ry RrYy rY ry F1 generation Genotype Genotypic Ratio Phenotype Phenotypic Ratio RRYY RrYy RrYY RRYy RRyy Rryy rrYY rrYy rryy 2. To simulate the two-factor cross above, select 4 pennies with masking tape covering both sides. One side of the tape should be capital letters (RRYY), and the other side should be lower case letters (rryy). 3. Place the 4 pennies in a cup. Shake the cup and toss the pennies onto your table. Place a tally into the corresponding genotype category in the table below. Toss the pennies 47 more times for a total of 48 tosses. 1 4. Count the tally marks for each phenotypic combination and record these totals in the appropriate place in the table below. Phenotypes Genotypes Number Number Toss Total Expected Expected Results Number for 16 for 48 Observed Offspring Offspring Rough, RRYY 9/16 Yellow RrYy Seeds RRYy RrYY Rough, RRyy 3/16 White Seeds Rryy Smooth, Yellow Seeds Smooth, White Seeds rrYY rrYy 3/16 rryy 1/16 Questions 1. When two homozygous plants with contrasting traits are crossed (PPxpp), what are the expected genotypes for the offspring? 2. What is the expected genotypic ratio for a one-factor cross of two heterozygous organisms (PpxPp)? 3. What is the expected phenotypic ratio for a one-factor cross of two heterozygous organisms (PpxPp)? 4. In your simulated two-factor cross with the coins, why might your actual experimental values have been different from the values you expected? 5. Why is it helpful to conduct a large number of trials when simulating genetic crosses? 6. How is an understanding of genetics useful to an animal or plant breeder? 7. Is it possible for two organisms to have different phenotypes but the same genotype? Explain your answer. 8. Is it possible for two organisms to have different genotypes but the same phenotype? Explain your answer. 9. How could a guinea pig breeder determine whether a rough-coated guinea pi is homozygous or heterozygous for this trait? 10. In dogs, wire hair is due to a dominant gene W. Two wire-hair dogs were mated and produced a puppy with smooth hair. What were the genotypes of the two parent dogs? 2