Genetics

Genetics is the branch of biology concerned with heredity and variation — how characteristics are passed from parents to offspring and why individuals differ. The hereditary instructions are carried by DNA, a long molecule made of two strands twisted into a double helix. The sequence of four chemical bases along the strands forms a code, and segments of DNA called genes each carry the instructions for a particular trait or protein. Genes are packaged into structures called chromosomes, and most organisms carry two copies of each chromosome, one from each parent.

The basic patterns of inheritance were first described by Gregor Mendel in the nineteenth century, before DNA was known. Studying pea plants, he showed that traits are passed on as discrete units, now called genes, and that different versions of a gene, called alleles, can be dominant or recessive. Mendelian genetics explains why a trait can skip a generation and how the combination of alleles inherited from two parents determines an offspring's characteristics.

At the molecular level, the information in DNA is used through RNA, a related molecule that copies a gene's code and carries it to the cell's protein-building machinery, where it directs the assembly of a specific protein. Modern genetics also includes recombinant DNA technology, in which DNA from different sources is combined, allowing scientists to transfer genes between organisms. These techniques underpin much of biotechnology, from producing medicines such as insulin to studying how genes cause disease. Genetics applies across all life, including plants, where it guides breeding and crop improvement.

Frequently asked questions

What is the difference between a gene and an allele?

A gene is a segment of DNA that codes for a trait. An allele is one of the different versions of that gene, such as the forms producing different eye colours.

What did Mendel discover?

Mendel showed that traits are inherited as discrete units that can be dominant or recessive, establishing the basic rules of inheritance before DNA was identified.

What is recombinant DNA?

Recombinant DNA is DNA assembled from more than one source. The technique lets scientists move genes between organisms, for example to produce medicines.