Question

Use the forked-line method to solve this problem (SHOW YOUR WORK): In cucumbers, there are 3 genetic traits, as follows: dull fruit is dominant to glossy fruit orange fruit color is dominant to cream fruit color bitter cotyledons are dominant to nonbitter cotyledons You cross a plant that is heterozygous for all 3 genes to another plant that is heterozygous for dull fruit but has cream fruit color and nonbitter cotyledons. Among the next generation, what proportion of the offspring will be a) dull, orange, bitter b) glossy, cream, nonbitter c) heterozygous for all 3 genes (HINT: it's not the same answer as a) above

Answer 1

Answer:

a) dull, orange, bitter ---->  3/16 D- Oo Bb

b) glossy, cream, nonbitter ---> 1/16 dd oo bb

c) heterozygous for all 3 genes ---> 2/16 Dd Oo Bb

Explanation:

Available data:

• dull fruit (D-) is dominant to glossy fruit (dd)
• orange fruit color (O-) is dominant to cream fruit color (oo)
• bitter cotyledons (B-) are dominant to non-bitter cotyledons (bb)
• Cross: a plant heterozygous for all 3 genes with a plant that is heterozygous for dull fruit but has cream fruit color and non-bitter cotyledons.

Parentals) Dd Oo Bb     x    Dd oo bb

To get the proportions of the offspring using the forked-line method, we must analyze each gene separately.

D gene:

Parentals) Dd    x    Dd

Gametes ) D   d    D    d

Punnett square)      D      d

                        D   DD    Dd

                        d    dD     dd

F1) 1/4 DD

     2/4 Dd

     1/4 dd

O gene:

Parentals) Oo    x    oo

Gametes) O    o     o     o

Punnett square)     O      o

                        o    Oo     oo

                         o    Oo    oo

F1) 1/2 Oo

     1/2 oo

B gene:

Parentals) Bb    x    bb

Gametes) B   b      b    b

Punnett square)   B        b

                  b         Bb      bb

                  b         Bb      bb

F1) 1/2 Bb

     1/2 bb

What proportion of the offspring will be

a) dull, orange, bitter

   (1/4 DD + 2/4 Dd) x 1/2 Oo x 1/2 Bb = 3/4 D- x 1/2 Oo x 1/2 Bb

   3/16 D- Oo Bb

b) glossy, cream, nonbitter

   1/4 dd x 1/2 oo x 1/2 bb

   1/16 dd oo bb

c) heterozygous for all 3 genes

    2/4 Dd x 1/2 Oo x 1/2 Bb

    2/16 Dd Oo Bb

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