AP BIOLOGY

Detailed explanation-1: -An international research effort called the Human Genome Project, which worked to determine the sequence of the human genome and identify the genes that it contains, estimated that humans have between 20, 000 and 25, 000 genes. Every person has two copies of each gene, one inherited from each parent.

Detailed explanation-2: -99.6. The DNA of any two people on Earth is 99.6 percent identical. But 0.4 percent variation represents about 12 million base pairs, which can explain many of the differences between individuals, especially if the changes lie in key genes. Our environment also contributes to our individuality.

Detailed explanation-3: -Scientists estimate that the human genome, for example, has about 20, 000 to 25, 000 protein-coding genes. Before completion of the draft sequence of the Human Genome Project in 2001, scientists made bets as to how many genes were in the human genome.

Detailed explanation-4: -You receive 50% of your genes from each of your parents, but the percentages of DNA you received from ancestors at the grandparent level and further back are not necessarily neatly divided in two with each generation.