Explain the molecular basis of this epistasis. Essentially, you need to describe

Question

Explain the molecular basis of this epistasis. Essentially, you need to describe the gene expression and regulatory steps that explain why a homozygous recessive mutation in either locus would result in yellow grapes.

Let's suppose that there is a locus (denoted by P) that controls fruit coloration in a species of grapes. For a really long time, farmers have known that there is a recessive mutation in the P locus, such that PP and Pp plants have purple grapes, whereas homozygous recessive pp plants have yellow grapes. More recently, plants with yellow grapes started showing up in a northern CA farm. So you first decide to determine if the old and newer mutations causing yellow grapes actually happen in the same gene or not. To that end, you cross a classic pp plant with one of the new NorCal mutants, and you obtain 100% progeny with purple grapes. In genetics, we call this "complementation, and it indicates that the new mutation is also recessive but in a different locus (that we will call T). What happened..? Let's take a look the classic pp plants must have had a wild type (normal) T locus (i.e.. they were DD TT). On the other

Explanation / Answer

These genes are complementary to one another In this when gene present alone these genes remain unexpressed, but they are expressed only when they are combined.

Bold marked has both the genes so it is purple in colour both the genes are expressed.

The parents developed yellow color because they lacked either gene P or gene T.

So the ratio is 9:7

PT Pt pT pt PT PPTT PPTt PpTT PpTt Pt PPTt PPtt PpTt Pptt pT PpTT PpTt ppTT ppTt pt PpTt Pptt ppTt pptt

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