We can use the basics of probability to determine the likelihood an offspring will express a trait. One way to do this is using punnet squares, where the genotype for each parent is placed on the left side and the top of the square, as seen below.
We would then fill in the remaining squares by taking one allele/contribution from the corresponding row and the second allele/contribution from the corresponding column. We will end up with two letters in each of the cells that are empty in the above example.
This would be our result:
We have four squares and four options. However, because all four of our options are the same (YG), the chance of having an offspring with the YG phenotype is 100%.
Here is another example of a genetics probability question on Socratic.