BIO hard question

[299678]

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A species of plant is discovered in which
individual plants produce either white or purple
flowers. True breeding plants that have short
stems with white flowers are crossed with true
breeding plants that have tall stems and purple
flowers. The resulting offspring all have tall stems
with purple flowers. When one of these tall,
purple-flowered offspring is crossed with a short,
white-flowered plant, plants with the following
characteristics were obtained in equal proportions.
White flowers on tall stems
Purple flowers on tall stems
White flowers on short stems
Purple flowers on short stems
Given the information above, which of the
following is most likely true?

(A) The white-flower allele and the tall-stem
allele occur at the same locus.
(B) The genes for flower color and stem length
are closely linked.
(C) Extensive crossing-over between the
purple-flower allele and the white-flower
allele has occurred.
(D) The genes for flower color and stem length
are not linked.
(E) Independent assortment does not occur in
this species of plant.
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Need ur brief reasoning

 

[UndergradGuy7]

I say D.

You are given that you start off with short, white and crossed with tall, purple. The result is tall, purple. So we know tall and purple is dominant.

So pptt x PPTT gives PpTt

Then we cross this PpTt with a pptt. If you do a square for this you will get 1:1:1:1.

If Mendel's laws (assortment, segregation) are obeyed and no linkage/crossing over occurs we get 1:1:1:1 ratio. Like in the square.

 

[Jps17kl]

I agree. In the beginning, TT PP x ttpp will give you 100% TtPp (tall, purp)

If TtPp is crossed with ttpp(short,white)

TtPp gametes- TP Tp tP tp
ttpp gametes- tp

so 25% TtPp, 25% Ttpp, 25% ttPp, 25% ttpp

we see that the ratio is already 1:1:1:1. so this indicates that no crossing over has occurred and the two genes are not linked. So I think D is true as well.

 

[299678]

Thanks