Explain why all male children of parent 1 (XY) and parent 2 (XX) are red-green color blind.

Here's the explanation for why all male children of parent 1 and parent 2 are red-green color blind:

1. Determine parental genotypes: Parent 1 is a male with normal color vision, so his genotype is $X^B Y$. Parent 2 is a female with red-green color blindness, so her genotype is $X^b X^b$.
2. Inheritance in males: Male children inherit their Y chromosome from their father (Parent 1) and their X chromosome from their mother (Parent 2).
3. Allele passed from mother: Since Parent 2 has the genotype $X^b X^b$, she can only pass on the $X^b$ allele to her sons.
4. Son's genotype and phenotype: Therefore, all male children will have the genotype $X^b Y$. As males only have one X chromosome, they will express the red-green color blindness trait.

This means the completed explanation is:
All male children receive the Y chromosome from the father and the $X^b$ chromosome from the mother. Therefore, all sons have the genotype $X^b Y$, which makes them red-green colour blind.