What is the role of DNA in inheritance and genetic variation?

DNA, or deoxyribonucleic acid, is the molecule that carries genetic information in all living organisms. It is a long, double-stranded chain of nucleotides, each of which contains a sugar, a phosphate group, and a nitrogenous base. The four nitrogenous bases found in DNA are adenine (A), thymine (T), cytosine (C), and guanine (G).

During sexual reproduction, an individual inherits half of its DNA from each parent. The DNA is passed on through the sex cells, which are the sperm and the egg. Each of these cells contains only half of the genetic information necessary to create a complete human being. When the sperm fertilizes the egg, the resulting zygote contains the full complement of genetic information, half from the father and half from the mother.

Genetic variation arises from mutations in DNA. Mutations can occur spontaneously, or they can be induced by exposure to radiation or chemicals. Mutations can be harmful, beneficial, or neutral, depending on their effects on the organism. Mutations that occur in the sex cells can be passed on to future generations.

One of the key mechanisms of genetic variation is genetic recombination. This occurs during meiosis, the process of cell division that produces sex cells. During meiosis, the homologous chromosomes in each parent undergo crossing over, which is the exchange of genetic material between the chromosomes. This creates new combinations of alleles, or variants of genes, in the offspring.