4) A vanilla bean plant with white-coloured flowers was self-crossed. The seeds

Question

4) A vanilla bean plant with white-coloured flowers was self-crossed. The seeds were collected and planted. The resulting progeny were 211 plants with white-coloured flowers and 55 plants with black-coloured flowers.

Write the genotypes of the parental plant and its progeny, using B and b to designate the different flower-colour alleles.

(a) Genotype of the parent with white-coloured flowers:

        (b) Genotype(s) of the progeny with white-coloured flowers (if more than one genotype is possible, please separate the genotypes with a comma and a space,

          e.g. BB, Bb, bb):

       (c) Genotype(s) of the progeny with black-coloured flowers (if more than one genotype is possible, please separate the genotypes with a comma and a space, e.g. BB, Bb, bb):

      Predict the phenotypic ratios for the crosses shown below: (5 marks) HINT: Use the genotypes you predicted above in Question 4 to assist you.

cross whitecolor flower black color flowers Parental white-flowered plant self-crossed Parental white-flowered plant crossed with a black-flowered plant from the F1 generation 3:1 Pure-breeding white-flowered plant crossed with a parental white-flowered plant Pure-breeding white-flowered plant test-crossed Pure-breeding black flowered plant crossed with a black-flowered plant from the F1 generation

Explanation / Answer

Parent plant: It must be heterozygote as its progeny shows segregation of phenotype.
Genotype of the parent plant = Bb
Phenotype = White flowers (Dominant phenotype)
Recessive phenotype = Black flowers

Parental cross: Bb X Bb
Progeny: BB (White) Bb Bb (White) bb (Black)
Genotypic ratio = 1:2:1
Phenotypic ratio = 3 (White): 1 (Black)

Genotype of the progeny plants with white flowers = BB or Bb
Genotype of the progeny plants with black flowers = bb

a. Parental white-flowered plants selfed = Bb X Bb
Progeny: BB (White) Bb Bb (White) bb (Black)
Genotypic ratio = 1:2:1
Phenotypic ratio = 3 (White): 1 (Black)

b. Parental white-flowered plant crossed with black plants = Bb X bb
Progeny: BB (White) Bb (White) bb (Black)
Genotypic ratio = 1:1
Phenotypic ratio = 1 (White): 1 (Black)

c. Pure breeding white-flowered plant crossed with parental white-flowered plants = BB X Bb
Progeny: BB (White) Bb (White)
Genotypic ratio = 1:1
Phenotypic ratio = 1 (All white)

d. Pure breeding white-flowered plants test crossed = BB X bb
Progeny: Bb (White)
Genotypic ratio = 1
Phenotypic ratio = 1 (All white)

e. Pure breeding black-flowered plants crossed with black flowered plants from F1 = bb X bb
Progeny: bb (Black)
Genotypic ratio = 1
Phenotypic ratio = 1 (All black)

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