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Using a Punnett Square

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Using a PUNNETT SQUARE. Place one of the parents on top, and one on the left. ... Use these genes: PP purple flowers. Ss smooth pea. Gg green pea ... – PowerPoint PPT presentation

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Title: Using a Punnett Square


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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