DNA is the genetic blueprint of living organisms. Chromosomes are made from DNA. Genes are short sections of DNA. Alleles are different forms of a gene (they can be dominant or recessive).
DNA
DNA (or deoxyribonucleic acid) is the molecule that carries the genetic information in all cellular forms of life and some viruses. It belongs to a class of molecules called the nucleic acids, which are polynucleotides - that is, long chains of nucleotides.
Chromosomes
The nucleus of each cell in our bodies contains approximately 1.8 - 2 metres of DNA in total, although each strand is less than one millionth of a centimetre thick. This DNA is tightly packed into structures called chromosomes, which consist of long chains of DNA and associated proteins. In eukaryotes, DNA molecules are tightly wound around proteins - called histone proteins - which provide structural support and play a role in controlling the activities of the genes. A strand 150 to 200 nucleotides long is wrapped twice around a core of eight histone proteins to form a structure called a nucleosome.
Gene
DNA (or deoxyribonucleic acid) is the molecule that carries the genetic information in all cellular forms of life and some viruses. It belongs to a class of molecules called the nucleic acids, which are polynucleotides - that is, long chains of nucleotides. A human being has 20,000 to 25,000 genes located on 46 chromosomes (23 pairs).
Genes consist of three types of nucleotide sequence:
Genes consist of three types of nucleotide sequence:
- coding regions, called exons, which specify a sequence of amino acids
- non-coding regions, called introns, which do not specify amino acids
- regulatory sequences, which play a role in determining when and where the protein is made (and how much is made)
Allele
An allele is a variant form of a gene, that is located at a specific position, or genetic locus, on a specific chromosome. Humans are called diploid organisms because they have two alleles at each genetic locus, with one allele inherited from each parent.