See introns . Gametes are produced by meiosis . They normally have half the number of chromosomes found in somatic cells. A gene may be made up of hundreds of thousands of DNA bases. Genes are responsible for hereditary characteristics in plants and animals.
Genetic mechanisms are the underlying foundation for evolutionary change.
Genetics is the branch of science that deals with the inheritance of biological characteristics. See Human Genome Project . Genotype can refer to an organism's entire genetic makeup or the alleles at a particular locus. See phenotype . Human sperm and ova normally contain only 23 chromosomes, which is the result of the halving of chromosome pairs in meiosis .