Single gene traits<span>: controlled by a </span>single gene<span> that has two alleles (ex: widow's peak) – only two phenotypes are possible – widow's peak or no widow's peak.</span>Polygenic traits<span>: controlled by two or more </span>genes. Has 2 or more alleles. One polygenic trait<span> can have many possible genotypes and phenotypes! </span>
The alveoli. These little air sacs are found on the end of the bronchioles and are the place where oxygen enters the blood and the carbon dioxide leaves.
