Explain a standard curve and mention what is its use

A standard curve is a tool that allows us to estimate the DNA concentration of unknown samples by comparing them to standards with known DNA concentrations.

the father in the first generation probably had the recessive colorblind trait in his x chromosome. if he and his wife both had the colorblind trait, even if she had 1 recessive and 1 dominant, then that trait would be passed on to their kids.

(since you didn't attach the family tree this is just an assumption)