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Dihybrid Crosses

Dihybrid Crosses. When is it used?. A dihybrid cross is exploring the possibilities of TWO traits. For example, what will the offspring look like when a yellow, wrinkled pea plant is crossed with a green, smooth pea plant. You are looking at two traits- pea color and pea texture.

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Dihybrid Crosses

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  1. Dihybrid Crosses

  2. When is it used? • A dihybrid cross is exploring the possibilities of TWO traits. For example, what will the offspring look like when a yellow, wrinkled pea plant is crossed with a green, smooth pea plant. You are looking at two traits- pea color and pea texture.

  3. Steps to Set up a DihybridPunnett Square • Write out allelic combination • USE THE F.O.I.L. method to set up PunnettSquare • F=first allele combination • O= outer allele combination • I= inner allele combination • L= last allele combination • Conduct the test cross • Evaluate the genotypes and phenotypes

  4. Practice Example • In summer squash, white fruit color (W) is dominant over yellow fruit color (w) and disk-shaped fruit (D) is dominant over sphere-shaped fruit (d)..  If a squash plant true-breeding for white, disk-shaped fruit  is crossed with a plant true-breeding for yellow, sphere-shaped fruit,  what will the phenotypic and genotypic ratios be for: • a. the F1 generation?     b. the F2 generation?

  5. 1. Write down the cross in terms of the parental (P1) genotypes and phenotypes: WWDD (white, disk-shaped fruit)    X   wwdd (yellow, sphere-shaped fruit) F= WD F=wd O= WD O=wd I=WD I= wd L=WD L= wd

  6. All F1 progeny will be heterozygous for both characters (WwDd)  and will have white, disk-shaped fruit . F2 generation will have two heterozygous parents crossed

  7. Determine the F2 gametesand write out all possible allele combinations • WwDdXWwDd F=WD F= WD O=Wd O=Wd I=wD I=wD L=wd L= wd

  8. Conduct the test cross

  9. Evaluate your results • Genotypic ratios: 1/16 will be homozygous dominant for both traits (WWDD)2/16 will be homozygous dominant for color and heterozygous for shape (WWDd)2/16 will be heterozygous for color and homozygous dominant for shape (WwDD)1/16 will be homozygous dominant for color and homozygous recessive for shape (WWdd)4/16 will be heterozygous for both traits  (WwDd)2/16 will be heteozygous for color and homozygous recessive for shape (Wwdd)1/16 will be homozygous recessive for color and homozygous dominant for shape (wwDD)2/16 will be homozygous recessive for color and heterozygous for shape (wwDd)1/16 will be homozygous recessive for both traits (wwdd)

  10. Phenotypic ratios:9/16 will have white, disk-shaped fruit3/16 will have white, sphere-shaped fruit3/16 will have yellow, disk-shaped fruit1/16 will have yellow, sphere-shaped fruit • This is a 9:3:3:1 phenotypic ratio.

  11. Practice this in your notes • President Obama and Michelle Obama want to have another child and want to figure out their chances of having certain traits in their offspring. They wonder about the following traits. • E= round eyes D= dark skin T= tall W= widows peak • e= oval eyes d= light skin t= short w= no widows peak

  12. Problem 1 BarackObama • 1-Homozygous Dominant eyes w/ heterozygous for height Michelle Obama • 1-Heterozygous for eyes w/ homozygous for height

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