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Suppose you hybridize two plants - One has a red flower and a long stalk, the other has a pink flower and a short stalk. This resulted in these 4 type of plants, with ratio 1:1:1:1

  1. Long stalk red flower
  2. Long stalk pink flower
  3. Medium stalk red flower
  4. Medium stalk pink flower

What possible genotype could the parents have that would result this way?

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Do you mean "genotype"? Unless I'm missing something, it seems like you've already described the phenotype (red/long and pink/short) of the parents in your first sentence. – Oreotrephes Aug 18 '13 at 9:47
up vote 4 down vote accepted

Flower Color

A Heterozygous (Rp) x Homozygous recessive (pp) cross can produce the distribution:

         p      p

   R    Rp     Rp  = Red, Red

   p    pp     pp  = pink, pink

Stalk Length

To me, there appears to be another allele involved or a lack of allele, and definitely Co-Dominance. The only way I could think of a way to get the ratio of stalk lengths in the question after a few minutes thought is if one of the plants are missing a gene before the cross (akin to Turner Syndrome) - the example that follows puts the missing gene on the Short-stalked parents:

SS = Short
TT = Tall
ST = Medium
SX = Short
TX = Tall
X = Missing Gene / Nothing

         S      X

   T    ST      TX = Medium, Tall

   T    ST      TX = Medium, Tall

So ultimately the cross would look like this:

        Sp     Xp

   TR   STRp   TXRp = (#3), (#1)

   Tp   STpp   TXpp = (#4), (#2)
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