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DIHYBRID PUNNETT SQUARES

DIHYBRID PUNNETT SQUARES. A tall plant is crossed with a short plant. What is the probability that the offspring will be short?. T=tall t=short. A cross that accounts for only one trait (e.g. height OR eye color OR shape). MONOHYBRID CROSS. Cross that accounts for two traits

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DIHYBRID PUNNETT SQUARES

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  1. DIHYBRID PUNNETT SQUARES

  2. A tall plant is crossed with a short plant. What is the probability that the offspring will be short? T=tall t=short

  3. A cross that accounts for only one trait • (e.g. height OR eye color OR shape) MONOHYBRID CROSS

  4. Cross that accounts for two traits • (e.g. Height AND color; dimples AND eye size) DIHYBRID CROSS

  5. Assign letters for the alleles • T=tall; t=short • Y=yellow; y=green SET UP THE DIHYBRID CROSS

  6. Homozygous dominant? • Homozygous recessive? • Heterozygous? • DETERMINE FOR BOTH TRAITS • (e.g. TTYY) DETERMINE THE PARENTS’ GENOTYPES

  7. Each parent can only pass down one allele for each trait to the offspring • E.g. TtYy parent can only pass down T OR t and Y or y WRITE THE POSSIBLE GAMETE COMBINATIONS

  8. 4x4 square = 16 total boxes!!! DRAW THE EMPTY SQUARE

  9. Write all possible gamete combinations for first parent on top • Write all possible gamete combinations for second parent on side INSERT PARENT INFO ON TOP AND SIDE OF THE SQUARE

  10. Write genotypes and phenotypes for possible offspring in the squares COMPLETE THE PUNNETT SQUARE

  11. Count phenotypes of offspring • (e.g. tall and yellow; tall and green; short and yellow; short and green) • Make the ratio DETERMINE THE PHENOTYPIC RATIO

  12. Count the genotypes and make the ratio • (e.g. TTYY, TTYy, TTyy, TtYY, TtYy, Ttyy, ttYY, ttYy, ttyy) DETERMINE THE GENOTYPIC RATIO

  13. If the question asks for a probability, use the “part divided by whole” formula • E.g. 8 out of 16 are yellow, so the probability of yellow is 8/16=1/2=.5=50% DETERMINE PROBABILITIES

  14. Do the problems on the back of the worksheet. NOW IT’S YOUR TURN!

  15. 3 Dihybrid Punnett Square s • Homework: Read 11-3, pg 274 #1-5 HOMEWORK

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