a. You would expect 300 long/green plants.
Since each of the long/yellow parent plants had a short/green parent, they are all heterozygous for both genes.
At each gene, there is a 25% chance of offspring being homozygous dominant, 25% homozygous recessive, and 50% heterozygous (which will have the dominant phenotype).
You're looking for long/green offspring. There is a 75% chance that any offspring will have the long phenotype and a 25% chance they will have the green phenotype.
Since you assume the genes are unlinked, you can multiply these probabilities together to get 3/16, which leads to 300 out of the 1600 progeny.
b. You would expect a 3:1 ratio because yellow is dominant to green and thus the heterozygotes would have the yellow phenotype.
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