Dihybrid Crosses When is it used A dihybrid
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.
Steps to Set up a Dihybrid Punnett Square • Write out allelic combination • USE THE F. O. I. L. method to set up Punnett Square – – 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
Practice Example • In summer squash, white fruit color (W) is dominant over yellow fruit color (w) and diskshaped fruit (D) is dominant over sphereshaped fruit (d). . If a squash plant truebreeding 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 F 1 generation? b. the F 2 generation?
1. Write down the cross in terms of the parental (P 1) 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
All F 1 progeny will be heterozygous for both characters (Ww. Dd) and will have white, disk-shaped fruit. WD WD wd Ww. Dd Ww. Dd F 2 generation will have two heterozygous parents crossed
Determine the F 2 gametes and write out all possible allele combinations • Ww. Dd X Ww. Dd F=WD F= WD O=Wd I=w. D L=wd L= wd
Conduct the test cross
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 (Ww. DD) 1/16 will be homozygous dominant for color and homozygous recessive for shape (WWdd) 4/16 will be heterozygous for both traits (Ww. Dd) 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 (ww. DD) 2/16 will be homozygous recessive for color and heterozygous for shape (ww. Dd) 1/16 will be homozygous recessive for both traits (wwdd)
• Phenotypic ratios: 9/16 will have white, disk-shaped fruit 3/16 will have white, sphere-shaped fruit 3/16 will have yellow, disk-shaped fruit 1/16 will have yellow, sphere-shaped fruit • This is a 9: 3: 3: 1 phenotypic ratio.
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
Problem 1 Barack Obama • 1 -Homozygous Dominant eyes w/ heterozygous for height Michelle Obama • 1 -Heterozygous for eyes w/ homozygous for height
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