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Using a Punnett Square

Using a Punnett Square. What is a PUNNETT SQUARE ?. A tool to predict the probability of certain traits in offspring that shows the different ways alleles can combine A way to show phenotype & genotype

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Using a Punnett Square

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  1. Using a Punnett Square

  2. What is a PUNNETT SQUARE? • A tool to predict the probability of certain traits in offspring that shows the different ways alleles can combine • A way to show phenotype & genotype • A chart that shows all the possible combinations of alleles that can result when genes are crossed

  3. What is a PUNNETT SQUARE? • Letters stand for dominant and recessive alleles • An uppercase letter stands for a dominant allele • Lowercase letters stand for recessive alleles

  4. Using a PUNNETT SQUARE To set up a Punnett square, draw a large square, and then divide it into 4 equal sections (also squares). It should look something like this:

  5. Using a PUNNETT SQUARE Now you need two parents to mate, ones with a known genotype For example, a red flower (genotype Rr) and a white flower (genotype rr). Rr x rr

  6. Using a PUNNETT SQUARE Place one of the parents on top, and one on the left. You should get a something similar to this:

  7. Using a PUNNETT SQUARE Finally, take each letter in each column and combine it with each letter from each row in the corresponding square. You should now have a picture close to this:

  8. Using a PUNNETT SQUARE • The two-letter combinations are the possible genotypes of offspring • They are: Rr, Rr, rr, and rr genotypes • From this it is possible to determine the probability (chance) that a flower will have a red phenotype (2/4 or 50%) or a white phenotype (2/4 or 50%)

  9. DiHybrid Cross • Determine all possible combinations of alleles in the gametes for each parent. • Half of the gametes get a dominant S and a dominant Y allele; • The other half of the gametes get a recessive s and a recessive y allele. • Both parents produce 25% each of SY, Sy, sY, and sy.

  10. Since each Parent produces 4 different combinations of alleles in the gametes, draw a 4 square by 4 square punnett square.

  11. The result is the prediction of all possible combinations of genotypes for the offspring of the dihybrid cross, SsYy x SsYy.

  12. What a about a Tri-Hybrid Cross? • Use these genes: • PP purple flowers • Ss smooth pea • Gg green pea

  13. Read More About Punnett Squares Here: World Builders: Punnet Squares E Viau CSULA

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