Definition of multiple alleles
There are multiple alleles in a population when there are many variations of a gene present. In organisms with two copies of each gene, also known as diploid organisms, each organism has the ability to express two alleles at the same time. They may be the same allelewhich is called genotype homozygous. Alternatively, the genotype may consist of alleles of different types, known as genotypes. heterozygous. Haploid organisms and cells have only one copy of a gene, but the population can still have many alleles.
In both haploid and diploid organisms, new alleles are created by spontaneous mutations. These mutations can arise in a number of ways, but the effect is a different sequence of nucleic acid bases in the DNA. The genetic code is “read” as a series of codons or triplets of nucleic acid bases corresponding to amino acids individual amino acids. A mutation causes the amino acid sequence to change, either simply or drastically. Simple changes that affect only a few amino acids can produce multiple alleles in a population, all of which function in much the same way, just to a different degree. Other mutations cause large changes in the protein created and it will not function at all. Still other mutations result in new forms of proteins that may allow organisms to develop new pathways, structures and functions.
Most of the time, scientists focus on the phenotypes created by certain alleles, and all all alleles are classified according to the phenotypes they create. However, a phenotype The genetic make-up of a particular phenotype may be due to a large number of mutations. Although humans have thousands of genes, they have more than 3 billion base pairs. This means that each gene consists of many base pairs. A mutation in any base pair can cause a new allele.
Multiple alleles combine in different ways in a population and produce different phenotypes. These phenotypes are caused by the proteins encoded by the various alleles. Although each gene encodes the same type of protein, different alleles can cause great variability in the function of these proteins. The fact that a protein functions at a higher or lower rate does not make it good or bad. This is determined by the sum of the interactions of all the proteins produced in an organism and the effects of the environment on those proteins. Some organisms, driven by multiple alleles in a variety of genes, function better than others and can reproduce more. This is the basis of natural selectionand as new mutations emerge and new lines of geneticsthe origin of the species takes place.
Examples of multiple alleles
Coat colour in cats
In domestic cats, breeding has been carried out for thousands of years by selecting different and varied coat colours. You can see long-haired, short-haired and hairless cats. There are genes that code for whether a cat will have fur or not. There are multiple alleles for this gene, some that produce hairless cats and some that produce hairy cats. Another gene regulates hair length. Long-haired cats have two recessive alleles, while a long-haired cat has two recessive alleles, while a short-haired cat has two recessive alleles. dominant allele will produce short hair.
Other genes control coat colour. There is one gene for several pigment colours: red, black and brown. Each gene has multiple alleles in the population, which express the protein responsible for producing the pigment. Each allele changes the way the protein functions and therefore the expression of pigment in the cat. Other genes similarly control the traits of curl, shading, patterning and even texture. The number of combinations and expressions of different genotypes together creates an almost infinite variety of categories. For this reason, cat breeders have been successfully trying for thousands of years to create new and bizarre varieties of cats and dogs. Even with only 4 alleles between two parents in each gene, the variety can be incredible. Just look at the kittens in the photo above.
Fruit flies
In 2000, the scientist finally succeeded in mapping the complex genome of the common fruit fly, Drosophilia melanogaster. The fruit fly had been and continues to be a valuable laboratory animal because of its high reproductive rate and the simplicity of maintaining and analysing large numbers of flies. At approximately 165 million base pairs, the DNA of a fruit fly is much smaller than that of a human. While a human has 23 chromosomes, a fruit fly has only 4. Yet, in just 4 chromosomes, there are about 17,000 genes. Each gene controls a different aspect of the fly and is subject to mutation and the emergence of new alleles.
In the image above, all the flies are of the same type. species Drosophilia melanogaster. The variation observed among flies is caused by multiple alleles in different genes. For example, the colour gene of the eye colour gene determines whether the fly will have an orange/brown eye, a red eye or a white eye. Both the white and orange alleles are recessive to the wild-type red eye allele. The two flies at the top have wild-type bodies, a tan with dark stripes. In the gene controlling body colour, two other alleles are present. The fly on the far right shows a homozygous recessive genotype causing a dark body. The three flies on the bottom show another homozygous recessive genotype, the yellow body mutation.
Other traits include everything from how the wings are formed to the shape of the antennae to the enzymes produced in the fly’s saliva. While 17,000 genes may not seem like that many, the total number of alleles in a population makes the total variety much greater than that. Each newly mutated allele adds another combination to the almost infinite pool of genetic variety.
- Homozygous: an individual with two of the same allele, as opposed to heterozygous individuals who have two different alleles.
- Mutation: the replacement of a base of nucleic acid in one gene with another nucleic acid, multiple nucleic acids or the removal of the nucleic acid altogether.
- Epistasis: when several genes produce an effect on the same trait, a fact true for most traits, even if it is difficult to see.