![]() If the father has two O alleles (OO), he has the blood group O. If a mother has the alleles A and O (AO), her blood group will be A because the A allele is dominant. Blood group A is said to have a dominant inheritance pattern over blood group O. So, a person with one A allele and one O allele (AO) has blood group A. The A allele is dominant over the O allele. Blood groupsįor blood groups, the alleles are A, B and O. (This is also the case if you have two alleles for brown eyes, BB.) However, if both alleles are for the recessive trait (in this case, blue eyes, bb) you will inherit blue eyes. So, if you have one allele for brown eyes and one allele for blue eyes (Bb), your eyes will be brown. The allele for brown eyes (B) is dominant over the allele for blue eyes (b). An allele of a gene is said to be dominant when it effectively overrules the other (recessive) allele.Įye colour and blood groups are both examples of dominant/recessive gene relationships. The most common interaction between alleles is a dominant/recessive relationship. mitochondrial – where the gene for a trait or condition is in your mitochondrial DNA, which sits in the mitochondria (powerhouse) of your cells.co-dominant – where each allele in a gene pair carries equal weight and produces a combined physical characteristic.Y-linked – where the gene for a trait or condition is on the Y-chromosome.X-linked recessive – where the gene for a trait or condition is recessive, and is on the X-chromosome.X-linked dominant – where the gene for a trait or condition is dominant, and is on the X-chromosome.autosomal recessive – where the gene for a trait or condition is recessive, and is on a non-sex chromosome.autosomal dominant – where the gene for a trait or condition is dominant, and is on a non-sex chromosome.Examples of inheritance patterns include: Alleles interact with each other in different ways. The two alleles in a gene pair are inherited, one from each parent. These two copies of the gene contained in your chromosomes influence the way your cells work. Changes (or variations) in the gene for that characteristic cause these different forms.Įach variation of a gene is called an allele (pronounced ‘AL-eel’). For example, blood type can be A, B, AB or O. Sometimes, one characteristic has many different forms. Some health conditions and diseases can be passed on genetically too. Parents pass on traits or characteristics, such as eye colour and blood type, to their children through their genes. Genes that are on the Y chromosome are said to be Y-linked. Genes that are on the X chromosome are said to be X-linked. 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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