15. Hydrangea macrophylla plants can have flowers that are blue, white or pink.

Question

15. Hydrangea macrophylla plants can have flowers that are blue, white or pink. White plants are never true breeding. Crossing two white plants results in 2/3 white and 1/3 colored flowers (all pink, all blue or some pink and some blue). When true breeding blue plants are crossed with true breeding pink plants the resulting F1 generation are all blue. When these F1 Blue plants are crossed with white plants the progeny are 3/8 blue, 1/8   pink and 1/2 white.

When cuttings from a large F1 blue hydrangea plant are planted all over a housing development about ½ the adult plants produce pink flowers the following year and ½ produce blue flowers. Note that all the plants in the housing development are genetically identical.

A. Discuss the data as it relates to allelic interactions? (2 pts)

B. Discuss the data in relation to gene interactions? (2 pts)

E. Given what you said above provide a comprehensive genetic hypothesis to explain above results. Be sure to include blue and pink true breeding plants, white plants, F1 offspring of white X white, blue F1, offspring of blue Fl X white, and blue F1 in housing development. Provide genotype and brief explanation of how genotype determines phenotype. (8 pts)

i. Explanation of of how genotype determines phenotype

ii.

Phenotype                                                      Genotype

True breeding blue

True Breeding pink

White plants

F1 offspring of White X White

            white

            pink

            blue

            pink and blue

F1 offspring offspring Blue X Pink

            Blue

Offspring of F1 Blue X white

  Blue

Pink

white

Explanation / Answer

i. Explanation of how genotype determines phenotype

There are two genes responsible for color. White is epistatic over colored. Let the symbol for white be 'W'. Blue is dominant over pink. Let the symbol for blue be 'B' and pink be 'b'.

ii.

Phenotype                                                      Genotype

True breeding blue: wwBB

True Breeding pink: wwbb

White plants: WwBb

F1 offspring of White X White

            White: W___        

            Pink: wwbb

         Blue: wwB_

Pink and blue: No plants are both pink and blue. Either the color will be pink or it will be blue.

I will explain the data line by line.

It is given that: White plants are never true breeding. Crossing two white plants (WwBb X WwBb) results in 2/3 white and 1/3 colored flowers (all pink, all blue or some pink and some blue). The results should have been 1/4 colored and 3/4 white. The result is differing because 'W' allele is not completely epistatic. In presence of 'B' penetrance of 'W' reduces.

When true breeding blue plants (wwBB) are crossed with true breeding pink plants (wwbb) the resulting F1 generation are all blue (wwBb). This shows that blue is dominant over pink.

When these F1 Blue (wwBb) plants are crossed with white plants (WwBb) the progeny are 3/8 blue, 1/8   pink and 1/2 white.

In this blue should be = 1/2*3/4 = 3/8 (proved)

White should be = 1/2 (proved); these are those plants who have received 'W' allele.

Pink should be = 1/2*1/4 = 1/8 (proved).

So, these results are consistent with the idea explained above.

When cuttings from a large F1 blue (wwBb) hydrangea plant are planted all over a housing development (wwbb) about ½ the adult plants produce pink flowers (wwbb) the following year and ½ produce blue flowers (wwBb).

All plants of housing development are genetically identical and having the genotype wwbb.

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