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So, clearly, the endosperm would be a fusion of the polar nuclei and one male gamete. Does this mean that each male gamete would have a T allele on it?

I can't seem to figure out a way to predict the allele distribution between the 2 polar nuclei since the flower has a Tt genotype.

Along the same lines, how can I predict what alleles the haploid egg would have? T or t? So, in that case, there would be a 50% chance of the embryo being TT and 50% chance of it being Tt (I didn't understand what the plus sign signifies).

The correct option is D, but I can't figure out how to get to that answer with absolute certainty.

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  • $\begingroup$ The question is unclear to me. I understand we expect a triploid nucleus plus a diploid zygote (double fertilization) but I don't understand what (TTT + TTt), TT means. $\endgroup$ – Remi.b Oct 13 '17 at 5:54
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IMO, the question is unclear

The question is unclear to me. I understand we expect a triploid nucleus plus a diploid zygote (double fertilization) but I don't understand what (TTT + TTt), TT means.

  • Which book did the question come from?

  • Is there any preamble to this question?

Double fertilization

I am not so used to thinking about double fertilization in plants. In short, two pollens are involved. One fertilize a haploid gamete from the mother and the other fuse with two haploid gamete (polar nuclei) from the mother (triple fusion) resulting in a triploid "individual".

In my below answer, I am assuming that any two polar nuclei can fuse with the pollen. I am not sure this is true. If it is systematically polar nuclei resulting from the same meiosis II (that is they have the same parent cell after meiosis I), then t story is a little different.

How I understand the question

In my understanding, we are talking about a single locus with two alleles T and t. Both pollens are T. The mother is Tt.

Answer

There are two possible gametes from the female side T and t. Only one possible gamete from the male side T. Therefore, the diploid zygote is either

  • $\frac{1}{2}$ TT
  • $\frac{1}{2}$ Tt

, where the numbers indicate probabilities

Now, for the triploid nucleus resulting from the fertilisation of two polar nucleus from the mother and one pollen grain can be either

  • $\frac{1}{4}$ TTT
  • $\frac{1}{2}$ TtT or tTT
  • $\frac{1}{4}$ ttT

Now, I have no idea how that matches to the possible answers as I don't understand the notation.

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