There are many genes located on the X chromosome, but only a few on the Y chromosome. A person with an XX pairing of sex chromosomes is biologically female, while a person with an XY pairing is biologically male.Īs well as determining sex, the sex chromosomes carry genes that control other body functions. Typically, the mother’s egg contributes an X chromosome, and the father’s sperm provides either an X or a Y chromosome. The chromosomes that determine the sex of the baby (X and Y chromosomes) are called sex chromosomes. When the sperm fertilises the egg, two copies of each chromosome are present (and therefore two copies of each gene), and so an embryo forms. A sperm and an egg each contain one set of 23 chromosomes. One copy is inherited from their mother (via the egg) and the other from their father (via the sperm). People usually have two copies of each chromosome. (Chromosome number 1 is the biggest.) These non-sex chromosomes are called autosomes. The paired chromosomes are numbered from 1 to 22 according to size. New genes are being identified all the time. These chromosomes contain between 20,000 and 25,000 genes. Humans typically have 46 chromosomes in each cell of their body, made up of 22 paired chromosomes and two sex chromosomes. Changes in the coding that makes a gene function can lead to a wide range of conditions. A change in a gene can occur spontaneously (no known cause) or it can be inherited. Sometimes, a gene contains a change that disrupts the gene’s instructions. The letter sequence of each gene contains information on building specific molecules (such as proteins or hormones – both essential to the growth and maintenance of the human body).Īlthough every cell has two copies of each gene, each cell needs only certain genes to be switched on in order to perform its particular functions. These letters are used like an instruction book. The genes are like a series of letters strung along each edge. Chromosomes are long strands of a chemical substance called deoxyribonucleic acid (DNA).Ī DNA strand looks like a twisted ladder. Almost every cell in the human body contains a copy of this blueprint, mostly stored inside a special sac within the cell called the nucleus. Your chromosomes contain the blueprint for your body – your genes.
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