The $N$ traits are independent of each other. For each trait, calculate the probability that the parents will produce the offspring's trait. Afterwards, multiply together the $N$ probabilities to get the answer. Therefore, if you can solve $N=1$, then you should be able to solve the entire problem.

Let's solve $N=1$. The parents will produce these $4$ traits with equal probability:

• Parent 1's first allele + Parent 2's first allele
• Parent 1's first allele + Parent 2's second allele
• Parent 1's second allele + Parent 2's first allele
• Parent 1's second allele + Parent 2's second allele

For example, if the parents' traits are Aa and Aa, then the offspring's trait will be:

• AA with probability $1/4$.
• Aa with probability $1/2$. Remember that aA is the same as Aa.
• aa with probability $1/4$.

Your code must handle all combinations of traits. Each of the $3$ traits could be AA, Aa, or aa. Also, the probability must be one of $\{0,1/4,1/2,1\}$.

Time complexity: $\mathcal{O}(N)$. There are $N$ traits and each trait takes $\mathcal{O}(1)$.