Genetics is the scientific study of genes – the instructions that govern a person’s growth, development, and health.
These are passed down from parents to children via sexual reproduction. Each cell in the human body has more than 20,000 genes stored in the cell’s nucleus. They provide the entire genetic code for a person and vary so that, apart from identical twins, each person has slightly different genes and has their own unique set of features.
Genes are found contained within long ribbon-like strands of deoxyribonucleic acid(DNA) molecules. Pairs of DNA molecules wind round in what is called a double helix. They are linked by chemical substances called bases, which are found in pairs. Long sequences of base pairs form genes. DNA can copy itself when cell division occurs so that a precise copy of the DNA is present in the new cell.
DNA is packaged into 23 pairs of chromosomes inside a cell. Twenty-two of these pairs are similar in men and women. The 23rd pair are the sex chromosomes. These consist of two X chromosomes in females (XX) and one X and one Y chromosome in males (XY). Male and female sex cells (sperm and eggs) contain just one of the two sex chromosomes. A male child develops if the sperm contains the Y chromosome.
Three generations of the same family share many similar features as a result of a parent and child sharing 99.95 per cent of the same DNA. A child inherits half of their chromosomes from their father and half from their mother. Sometimes, the genes from each parent, such as hair colour, do not match. In these cases, the dominant gene wins and is inherited by the child.
HUMAN GENOME PROJECT
Genome is all the genetic material contained in a full set of chromosomes. In 1990, an international project began to identify all the thousands of genes and the sequences of the nearly 3,100 million base pairs in human DNA. The identification was completed in 2003, but research continues to understand more about how genes work and how gene therapy might be able to replace faulty genes.
Crime-fighting agencies use DNA fingerprinting to trace identities of criminals and victims.
A DNA fingerprint is constructed by first taking a sample of DNA from a person’s blood, hair, or a swab inside their mouth. A complex series of processes sees DNA extracted from the nucleus of a cell, cut into smaller pieces, processed, and imaged using X-ray photography. New DNA samples can be compared to those already held in order to try to find a match.
Scientists are able to produce copies of individual genes, cells, and, in some cases, entire organisms, in processes called cloning. Scientists have cloned many animals, including sheep and cats. These creatures were created using somatic cell nuclear transfer. This is where the cell nucleus from an adult animal is placed inside an egg cell that has had its own nucleus removed.