What phenotypes would this cross produce and in what ratios?

In watermelons, solid green color (G) is dominant over striped, ad short shape (L) is dominant over long shape. Suppose a homozygous plant with long green fruit is crossed with a plant that is heterozygous for both of these characteristics.

1 Answer
Sep 19, 2016

50% solid long and 50% solid short. See explanation below.


This is a dihybrid cross, which means you have to look at how two traits are inherited. Let's take it step by step.

Step 1
List the possible traits and whether they are dominant or recessive:

  • solid green = dominant #-># G
  • striped green = recessive #-># g
  • short = dominant #-># L
  • long = recessive #-># l

Step 2
Determine the genotypes of the parents:

  • parent 1: homozygous solid green long = GGll
  • parent 2: heterozygous for both = GgLl (solid green short)

Step 3
Determine the gametes of the parents as depicted in the image for parent 2 (GgLl):

Home made illustration

The possible gametes for parent 2 are: GL - Gl - gL - gl

Step 4
Make a punnet square with the gametes of parent 1 and parent 2:

Home made illustration

Step 5
Determine the geno- and phenotypes and their ratios (see image).
There are no striped melons in this generation offspring, but some of the offspring do carry this trait. This can show up in next generations.

Note that in this case all the gametes of parent 1 are the same, therefore the first row would be enough to determine the ratios.