Question

In peas, green pods (g) are dominant over yellow pods. if a homozygous dominant plant is crossed with a homozygous recessive plant, what will be the phenotype of the f 1 generation? if two plants from the f 1 generation are crossed, what will the phenotype of their offspring be?

Answer 1

Based on the assumptions above, the Parental generation will have a genotype of GG and gg. This means the f1 generation will have a heterozygous genotype. In a Punnet square it will look like this:
     G     G
g  Gg    Gg
g  Gg    Gg

The phenotype of the F1 generation then will be Green. This is because the dominant trait or G will be expressed in a Gg combination. In other words, as long as there is a capital letter in the Genotype combination, the trait represented by the capital letter will be expressed.  

Now if you have two plants from the F1 generation crossed, some variety will appear. Taking the genotype of the two plants in that generation, Gg, we can construct another Punnet square to see the result:

      G     g
G  GG  Gg
g   Gg   gg

The phenotype will then be the following:
3 out of 4 off springs will be phenotype green.
1 out of 4 off springs will be phenotype yellow

In other words, there is a 75% chance of having a green off spring and a 25% chance of having a yellow off spring.