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← Punnett Squares

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Showing Revision 1 created 09/29/2013 by Cogi-Admin.

  1. In genetics, understanding how allele pairs segregate in
  2. all their possible combinations for all the chromosomes, and
  3. then recombine in the offspring at fertilization to produce
  4. all the different genotypes and phenotypes we can get,
  5. is one of the most complicated parts of genetics.
  6. We're only scratching the surface here really understanding what's
  7. going on in miosis. So there's a handy way
  8. of thinking about how these allele pairs separate using
  9. a tool called a punnet square. Now some of you
  10. may have heard of this before. We're going to take a
  11. quick look at how we can use punnet squares to
  12. help us understand this segregating alleles problem a little better.
  13. Let's imagine for a second that we have two parents.
  14. a mom and a dad. These are two individuals here
  15. and we're going to focus only on chromosome two, which has
  16. the lactase gene controlling lactose intolerance. Dad is homozygous recessive
  17. for lactase non-persistence. This means that dad is
  18. going to be lactose intolerant, because he's not going to make
  19. enough lactase as an adult To be able to
  20. metabolize lactose. Mom on the other hand is homozygous-dominant
  21. for lactase persistence. This means mom is going
  22. to be lactose tolerant, she's going to keep expressing lactase
  23. into adulthood. Now the question is, if they have
  24. a child What are the possible genotypes and phenotypes
  25. of their children? This is when our punnet squares
  26. are going to come in handy. Let's take the possible segregated
  27. allele combinations we can have for the dad. If
  28. his pair of homozygous recessive alleles segregate, we can get
  29. one gamete with a recessive allele, and another gamete
  30. with a recessive allele. Now we can do the same
  31. thing for the mom here. She can either pass
  32. on a dominant allele or another dominant allele. So if
  33. we want to figure out what their offspring could be, genotypically,
  34. or what genotype they will be, all we have to do
  35. is fill in this punnet square. Look at this box, combine
  36. the column and the row. We can have a plus and
  37. a minus here. You can have a plus and a
  38. minus here. You can have a plus and a minus here.
  39. You can have a plus and a minus here. It turns
  40. out that all the possible combinations appear to be the same.
  41. So, based on these results, what percentage of the children will be lactose
  42. intolerant, like the dad? Go ahead and put your answer and percentage form here.