In cucumbers, dull fruit (D) is dominant over glossy (d) fruit, orange fruit (R)

Question

In cucumbers, dull fruit (D) is dominant over glossy (d) fruit, orange fruit (R) is dominant over cream fruit (r), a bitter cotyledon (B) is dominant over non-bitter cotyledons (b). The three characters arc encoded by genes located on different pairs of chromosomes. A plant homozygous for dull, orange fruit and bitter cotyledons is crossed with a plant that is homozygous for glossy, cream fruit and non-bitter cotyledons. Assume that all 3 traits are encoded by independent genes. Write out the parental cross described above: _____ An F_1 plant from the cross described above is crossed with a plant having the genotype DdrrBb. Write out this cross involving the F, plant using proper genotypic annotation: Construct a COMPLETE branched diagram for this cross that reflects correct genotypes, phenotypes, and proportions at ALL branch points and for all resulting offspring. COMBINE multiple genotypes with same phenotype!

Explanation / Answer

All of the F1 plants have dull, orange fruit and bitter cotyledons (DdRrBb). By intercrossing the F1, the F2 are produced. The expected phenotypic ratios in the F2 can be calculated more easily by examining the phenotypic ratios produced by the individual crosses of each gene locus.

                F1 are intercrossed: DdRrBb × DdRrBb

         Locus 1: Dd × Dd = ¾ dull (DD and Dd); ¼ glossy (dd)

         Locus 2: Rr × Rr = ¾ orange (RR and Rr); ¼ cream (rr)

         Locus 3:             Bb × Bb = ¾ bitter (BB and Bb); ¼ nonbitter (bb)

Phenotypes and their expected proportions in the F2.

      dull, orange, bitter: ¾ dull × ¾ orange × ¾ bitter = 27/64

      dull, orange, nonbitter: ¾ dull × ¾ orange × ¼ nonbitter = 9/64

      dull, cream, bitter: ¾ dull × ¼ cream × ¾ bitter = 9/64

      dull, cream, nonbitter: ¾ dull × ¼ cream × ¼ nonbitter = 3/64

      glossy, orange, bitter: ¼ glossy × ¾ orange × ¾ bitter = 9/64

      glossy, orange, nonbitter: ¼ glossy × ¾ orange × ¼ nonbitter = 3/64

      glossy, cream, bitter: ¼ glossy × ¼ cream × ¾ bitter = 3/64

      glossy, cream, nonbitter: ¼ glossy × ¼ cream × ¼ nonbitter = 1/64

An F1 plant is crossed with a plant that has glossy, cream fruit and nonbitter cotyledons. the phenotypes and expected proportions among the progeny of this cross:

             Intercrossing the F1 with a plant that has glossy, cream fruit, and nonbitter cotyledons is an example of a testcross. All progeny classes will be expected in equal proportions, since the phenotype of the offspring will be determined by the alleles contributed by the F1 parent.

             DdRrCc (F1) × ddrrcc (tester)

      F1 Locus 1 (Dd):      ½ D and ½ d

      F1 Locus 2 (Rr):       ½ R and ½ r

      F1 Locus 3 (Cc):      ½ C and ½ c

      dull, orange, bitter: ½ dull × ½ orange × ½ bitter = 9/64

      dull, orange, nonbitter: ½ dull × ½ orange × ½ nonbitter = 9/64

      glossy, orange, bitter: ½ glossy × ½ orange × ½ bitter = 9/64

      glossy, orange, nonbitter: ½ glossy × ½ orange × ½ nonbitter = 9/64

      glossy, cream, bitter: ½ glossy × ½ cream × ½ bitter = 9/64

      glossy, cream, nonbitter: ½ glossy × ½ cream × ½ nonbitter = 9/64

Related Questions

Navigate

• Browse (All)
• Browse I
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.