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Punnett Squares

Punnett Squares. Mr. Chapman Science 9. How Do We Predict Inheritance of Traits?. Imagine that you wanted to know what the offspring of two parents would look like. We can use our current knowledge of genetics to make some basic predictions about future generations.

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Punnett Squares

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  1. Punnett Squares Mr. Chapman Science 9

  2. How Do We Predict Inheritance of Traits? • Imagine that you wanted to know what the offspring of two parents would look like. • We can use our current knowledge of genetics to make some basic predictions about future generations. • To do so, we use a Punnett Square.

  3. Punnett Squares • Punnett Squares are useful tools that allow us to predict the genotypes (and phenotypes) of a generation of offspring between two parents. • The first generation of offspring will be called F1. The second generation of offspring will be called F2. • Generally, we will only be asked questions about the first generation of offspring. Occasionally, however, we will be interested in the second generation as well.

  4. Example Question An allele for flower colour in plants is represented by the letter P. A homozygous purple plant and a homozygous white plant are bred together. Given that purple flower colour is the dominant trait, answer the following questions: • What is the genotype of the purple plant? • What is the genotype of the white plant? • What percentage of the F1 offspring will be purple coloured flowers?

  5. How can we predict these results? We Use a Punnett Square!

  6. How can we predict these results?

  7. How can we predict these results? • Parent 2 • Parent 1 • We fill in the extremities of the square with the parent’s alleles for the traits. • We fill in the remaining squares for each possible combination.

  8. How can we predict these results?

  9. How can we predict these results?

  10. How can we predict these results?

  11. How can we predict these results?

  12. How can we predict these results? • These results show that all the F1 offspring are all purple coloured hybrids, as they all possess the dominant purple allele for flower colour.

  13. How can we predict these results? • We can use another Punnett square to predict the F2 offspring. • The F2 offspring are a result of two offspring from the first cross being mated with each other. • In your notebook, attempt to predict the genotypes of a cross between two of the offspring.

  14. How can we predict these results? • We can use another Punnett square to predict the the F2 offspring.

  15. How can we predict these results? • We can use another Punnett square to predict the the F2 offspring.

  16. How can we predict these results? • We can use another Punnett square to predict the the F2 offspring.

  17. How can we predict these results? • We can use another Punnett square to predict the the F2 offspring.

  18. How can we predict these results? • We can use another Punnett square to predict the the F2 offspring.

  19. How can we predict these results? • We can use another Punnett square to predict the the F2 offspring.

  20. How can we predict these results? • The F2 offspring consist of:

  21. How can we predict these results? • The F2 offspring consist of:1 PP

  22. How can we predict these results? • The F2 offspring consist of:1 PP2 Pp

  23. How can we predict these results? • The F2 offspring consist of:1 PP2 Pp1 pp

  24. How can we predict these results? • The F2 offspring consist of:1 PP: purple coloured2 Pp1 pp

  25. How can we predict these results? • The F2 offspring consist of:1 PP: purple coloured2 Pp: purple coloured1 pp

  26. How can we predict these results? • The F2 offspring consist of:1 PP: purple coloured2 Pp: purple coloured1 pp: white coloured

  27. How can we predict these results? • The F2 offspring consist of:1 PP: purple coloured2 Pp: purple coloured1 pp: white coloured ¾ purple coloured

  28. How can we predict these results? • The F2 offspring consist of:1 PP: purple coloured2 Pp: purple coloured1 pp: white coloured  ¼ white coloured ¾ purple coloured

  29. How can we predict these results? • The F2 offspring consist of:1 PP: purple coloured2 Pp: purple coloured1 pp: white coloured  ¼ white coloured • The phenotype ratio for this generation is 3:1. ¾ purple coloured

  30. Example Question #2 • The gene for eye colour is represented by the letter B. Dominant eye colour, B, is brown while recessive eye colour, b, is blue. A heterozygous brown-eyed woman and a blue eyed man have four children. Answer the following questions: • How many of the four children will have blue eyes? • If the couple were to have 20 children, approximately how many of them, on average, would have blue eyes?

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