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Determining Probability of Genetic Outcomes

Determining Probability of Genetic Outcomes. Featuring the Punnett Square. 8 th Grade Science – K. Franklin – 8/25/10. Problem: What will the outcome be if a tall plant is crossed with a short plant?.

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Determining Probability of Genetic Outcomes

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  1. Determining Probability of Genetic Outcomes Featuring the Punnett Square 8th Grade Science – K. Franklin – 8/25/10

  2. Problem: What will the outcome be if a tall plant is crossed with a short plant? http://www.emc.maricopa.edu/faculty/farabee/biobk/biobookgenintro.html#The%20Monk%20and%20his%20peas

  3. Phenotype • Is the physical appearance of a trait. • The plant on the left has a Tall phenotype. • The plant on the right has a Short phenotype.

  4. Alleles or Genes (t) lower case letters = recessive traits • Are inherited “factors” (Mendel’s term) that control traits for each characteristic. • Living things have 2 for each trait. (One from each parent) • We use letters to represent alleles or genes. (T) capital letters = dominant traits

  5. “Tallness” is a dominant trait T = Tall “shortness” is a recessive trait t = short

  6. Genotype • Is the combination of alleles (type of genes).

  7. We’ll use a Punnett Square as a graphic organizer to help us figure out the probability of outcomes.

  8. 1st: The Parent’s alleles Go on the outside Parent 1 Parent 2

  9. 1st: Write the parent’s alleles correctly. Parent 1 Purebred tall T T t Purebred short Parent 2 t

  10. 2nd: Bring the alleles from Parent 1 down. Parent 1 T T T T t Parent 2 T T t

  11. 3rd: Bring the alleles from Parent 2 over. Parent 1 T T T T t t t Parent 2 T t t T t

  12. 4th: Look at the different possibilities of outcomes. Parent 1 T T T T t t t Parent 2 T t t T t

  13. What is the Probability of a tall plant? 1. Look for the capital T T T Heterozygous Heterozygous 2. Count the number of squares with a dominant allele. T T t t t The phenotype for this genotype is TALL 4 out of 4 possibilities = a 100% chance of a tall plant. T t t T t Heterozygous Heterozygous

  14. What is the Probability of a short plant? 1. Look for a double recessive (tt) T T Heterozygous Heterozygous 2. Count the number of squares with double recessive alleles. T T t t t 0 out of 4 possibilities = a 0% chance of a short plant. Heterozygous Heterozygous T t t T t

  15. What are the possible outcomes if the hybrids are crossed? T t T Now the first generation will serve as “parents” of the next generation. t

  16. 2nd: Bring the alleles from parent 1 down. T t T t T t T t

  17. 3rd: Bring the alleles from Parent 2 over to the right. T t T T T t T T t t t t

  18. 4th: Check the probability T t Homozygous Dominant Heterozygous T T T t T 1 out of 4=25% 2 out of 4=50% Homozygous Recessive Heterozygous T t t t t 1 out of 4=25%

  19. What is the probability of a shortPhenotype? t T Homozygous Dominant Heterozygous T T T t T Tall Tall 3 out of 4=75% Homozygous Recessive Heterozygous 1 out of 4=25% T t t t t Tall Short

  20. What is the probability of a Homozygous Recessive Genotype? t T Homozygous Dominant Heterozygous T T T t T Homozygous Recessive Heterozygous T t t t t 1 out of 4=25%

  21. More Practice • Read all about it! Textbook pp. 62-64 • Use one of these websites for additional practice as a class or for enrichment at home: • http://www2.edc.org/weblabs/Punnett/punnettsquares.html • http://www2.edc.org/weblabs/Mendel/MendelMenu.html

  22. Now You Try! Complete the worksheet that your teacher gave you!

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