Allele

Your body has tiny parts that tell it how to grow.

These parts can be slightly different. One part might make a flower purple. Another part might make it white.

Most of these small changes do not change how you look. Some changes can change things, like blood types. You get two sets of these parts. If they are the same, you are one way. If they are different, you are another way. These tiny parts make every living thing special.

Inside your body, there are tiny parts called DNA. DNA has special spots called loci. At each spot, there can be different versions. We call these versions alleles.

Most alleles do not change how you look. But some alleles change things. They can change flower colors. They can even cause diseases in humans. Gregor Mendel studied this with pea plants. He found that one gene had two alleles. One made flowers purple and one made them white.

Most living things have two sets of chromosomes. This means you have two alleles for every spot. If the alleles are the same, you are homozygous. If they are different, you are heterozygous.

Sometimes, one allele is dominant. A dominant allele masks the other one. The other allele is called recessive. You only see a recessive trait if you have two of them. This is how some genetic diseases work. For example, albinism is caused by recessive alleles. Blood types also use alleles. The ABO gene has six common alleles. These alleles decide if you have Type A, B, AB, or O blood.

Inside your DNA, there are specific spots called loci. At each locus, there can be different versions of a sequence. We call these different versions alleles.

Most alleles cause no change to a living thing. However, some alleles create different observable traits, called phenotypes. These can range from antibiotic resistance in bacteria to different colors in flowers. Some alleles even cause genetic diseases in humans.

Most multicellular organisms are diploid. This means they have two sets of chromosomes. Because of this, an organism has two alleles for every locus. If the two alleles are the same, the organism is homozygous. If the alleles are different, the organism is heterozygous.

In many cases, these alleles interact in a specific way. One allele might be dominant, which masks the effect of the other. The other allele is then called recessive. You only see a recessive phenotype if the organism is homozygous for that allele.

Gregor Mendel was a scientist who discovered how these work. He studied pea plants to see how traits pass to offspring.

Mendel found that flower color was controlled by a single gene. This gene had two alleles: one for purple and one for white. His work led to three laws of inheritance. These laws help us understand how alleles move from parents to their progeny. The word allele is a short form of allelomorph. This term was coined by British geneticists William Bateson and Edith Rebecca Saunders in 1902.

We can see alleles working in our own blood types. The ABO gene controls our blood groups. This gene has six common alleles. These alleles create four different phenotypes: Type A, Type B, Type AB, and Type O.

A person with Type A blood might have the genotype IAIA or IAi. A person with Type AB blood has the genotype IAIB. Even though we use these simple names, there are actually more than 70 alleles at this locus. Scientists have found that most gene loci are highly polymorphic, meaning they have many different versions.

Alleles connect to many parts of our lives and health. Some genetic disorders happen when a person gets two recessive alleles. Examples include albinism, cystic fibrosis, and Tay–Sachs disease. Other disorders, like Huntington's disease, happen with just one dominant allele. Some traits, like red–green color blindness, are more common in males. This is because the gene is on the X chromosome. Understanding alleles helps us see the tiny instructions that make every living thing unique.

An allele is a specific version of a DNA sequence. This sequence sits at a particular location on a DNA molecule. Scientists call this specific location a locus. Alleles are what make individuals different from one another. They can differ by just one single nucleotide. They can also involve much larger changes. These changes might include insertions or deletions of thousands of base pairs.

Most alleles cause very little change in an organism. However, some alleles result in different observable traits, known as phenotypes. For example, bacteria can have alleles for antibiotic resistance. Fruit flies can have alleles that cause developmental mutations. In humans, different alleles can lead to various genetic diseases. These variations are the building blocks of biological diversity.

Nearly all multicellular organisms are diploid. This means they carry two sets of chromosomes. Because of this, an organism has two alleles for every locus. If both chromosomes carry the same allele, the organism is homozygous. If the two alleles are different, the organism is heterozygous.

These combinations determine how traits appear in a living thing.

Alleles often interact through dominance and recessiveness. This describes how a heterozygote looks compared to a homozygote. A dominant allele masks the effect of a recessive allele. In a heterozygote, the dominant allele creates the phenotype. You only see a recessive phenotype if the organism is homozygous recessive. Some traits do not follow this simple pattern. They may involve co-dominance or polygenic inheritance instead.

Gregor Mendel was a key figure in this field. He discovered that pea plant flower colors resulted from a single gene. This gene had two alleles: one for purple and one for white. His work led to three laws of inheritance. These laws explain how alleles pass to progeny, or offspring. The term "allele" is short for "allelomorph." British geneticists William Bateson and Edith Rebecca Saunders coined this in 1902. The word comes from Greek roots meaning "other form."

We can see these rules in the ABO blood group system. This system is controlled by the ABO gene. This gene has six common alleles. These alleles produce four distinct phenotypes: Type A, Type B, Type AB, and Type O.

A person with Type A blood might have the genotype IAIA or IAi. A person with Type AB blood has the genotype IAIB. A person with Type O blood has the genotype ii. While we use these simple categories, more than 70 alleles are actually known at this locus.

Many genetic disorders are caused by alleles. Some occur when a person inherits two recessive alleles. Examples include albinism, cystic fibrosis, and Tay–Sachs disease. Other disorders happen with just one dominant allele, such as Huntington's disease. Some conditions are more common in males. This occurs when the gene is on the X chromosome. Examples include red-green color blindness and fragile X syndrome.

Science continues to find new ways to study these variations. Researchers have discovered epialleles. These are heritable marks like DNA methylation. They are different from traditional alleles because they are not defined by nucleotide sequences. In mycology, scientists use the term "idiomorph." This describes sequences at the same locus that have no similarity. Understanding alleles helps us map the complex history of life.