The punnett square cross they show you is between the genotypes Bb and bb. (See the Bb and bb at the top and right?)
Heterozygous means with one dominant gene (uppercase letter, in this case B) and one recessive gene (lowercase letter, in this case b).
The cross is already done for you. The 4 letter combinations that result from the cross of Bb and bb show as: Bb, bb, Bb, and bb. Using what we know, an individual that is <u>heterozygous</u> should have one B and one b (Bb). <u>2 out of 4</u> of the crosses are Bb. With basic math, that's then 50%.
By changing a gene's instructions for making a protein, a mutation can cause the protein to malfunction or to be missing entirely. When a mutation alters a protein that plays a critical role in the body, it can disrupt normal development or cause a medical condition
