Draw a punnet square between two carriers of cystic fibrosis and from this, work out the odds of their child being affected with CF.

I will draw the punnet square on the whiteboard. After drawing it, the ratio of CC:Cc:cc will be 1:2:1 As a recessive gene, only people with the homozygous recessive genotype (cc) will have cystic fibrosis so the odds of their child being affected will be 1/4 or 25%