AP BIOLOGY

Detailed explanation-1: -The number of phenotypes produced for a given trait depends on how many genes control the trait. Height in humans is an example of a single-gene trait . Each gene of a polygenic trait often has two or more phenotypes . A single polygenic trait often has many possible genotypes .

Detailed explanation-2: -Each chromosome contains thousands of individual genes. There are thought to be about 20, 000 genes in human DNA. Interestingly, the number of genes in human DNA is not appreciably different from the number of genes in chimpanzees or mice. Most traits are determined by more than one gene.

Detailed explanation-3: -Mendel found that two factors-one from a sperm cell and one from an egg cell-control each trait. Dominant traits block the expression of recessive traits. Recessive traits are expressed only when two recessive factors are present.

Detailed explanation-4: -Genes are contained in chromosomes, which are in the cell nucleus. A chromosome contains hundreds to thousands of genes. Every normal human cell contains 23 pairs of chromosomes, for a total of 46 chromosomes. A trait is any gene-determined characteristic and is often determined by more than one gene.