Notes on Multiple Allele

The phenotypic manifestation of a given trait is determined by the presence or absence of alleles, which are different variants of a gene (for example, brown eyes versus blue eyes). A polymorphic gene is one that has at least two alleles. Multiple allele circumstances occur when a gene can have three or more alleles in its various allele forms. The fact that multiple alleles are present and are maintained in a population is vital to keep in mind, but each individual has only two of them (at equivalent loci on homologous chromosomes).

Definition of Multiple Alleles

Alleles are produced by spontaneous mutations in both haploid and diploid species. They can occur in many ways, but the result is an altered sequence of DNA nucleotides. Amino acids are represented in the genetic code by a sequence of codons or triplets of nucleic acid bases. A mutation alters the amino acid sequence, either in a minor or major way, depending on the mutation. Multiple alleles can be produced in a population by small mutations that modify only a few amino acids, all of which perform nearly the same functions, albeit to varying degrees. It will not function at all if other mutations induce major alterations in the protein that is generated. Other mutations result in unique protein forms, allowing organisms to create new pathways, structures, and activities.

Important Facts on Multiple Alleles

There are many different alleles, and each has a distinct phenotype that scientists use to categorise them. However, several mutations can result in the same phenotype. Humans have more than 3 billion base pairs, despite having thousands of genes. In other words, each gene contains a staggering number of base pairs. A new allele can be produced by a mutation in any nucleotide pair.

In a population, different phenotypes, i.e., characteristics or traits, are created by a combination of different alleles. The proteins that the various alleles code for are responsible for these traits. Even though each gene codes for the same type of protein, many alleles can lead to a substantial variation in how these proteins function. No matter how fast or slow a protein works, that doesn’t mean it is good or bad. A person’s overall health is determined by the sum of the interactions between all of the organism’s proteins and the environment in which they interact. Some organisms outperform and outproduce others due to the presence of numerous alleles in various genes. As new mutations occur and new lines of genetics are produced, the genesis of species takes place through natural selection.

Examples of Multiple Alleles

Cats

For thousands of years, domestic cats have been bred to produce a wide range of coat colours. Cats can have long hair, short hair, or no hair at all, depending on the individual cat. The presence or absence of hair in a cat is determined by a set of genes. Some alleles of this gene create hairless cats, whereas other alleles produce cats covered with fur. The length of the hair is controlled by a different gene. Cats with long hair have two recessive alleles, while those with short hair have one dominant allele.

Kittens

Hair and fur colour are determined by several genes. Red, black, and brown pigments are all encoded by separate genes. Colour-making proteins are expressed by numerous alleles of each gene in a population. A kitten’s pigment expression is altered by each allele’s impact on the protein’s function. Curliness, shading, patterning, and even texture are also controlled by other genes in a similar manner. There is a nearly unlimited number of possible cats based on various genotype combinations and expressions. So, breeders have been seeking to generate new and different sorts of cats and dogs for thousands of years, to little avail. There can be a surprising amount of variation between parents, even if only four alleles are shared at each gene.

Flies

Individual flies differ because of numerous alleles in various genes. When it comes to eye colour, for example, the gene controls whether the fly will have an orange/brown or red eye. The wild-type red-eye allele is recessive to both white and orange alleles.

Wild-type bodies that are tan with dark stripes are found on the two flies at the top. Two more alleles exist in the gene that regulates skin tone. On the far right, a fly has a dark body because of a recessive gene. Another homozygous recessive genotype may be seen in the three flies at the bottom, namely the yellow body mutation.

Human Blood Groups

The ABO blood group system in human beings is an example of multiple alleles.Human beings have four blood groups or blood group phenotypes – A, B, AB and O.The blood groups are determined by two types of antigens present in the surface coating of red blood cells–A and B.

Conclusion

When a gene has many variants, multiple alleles might be found in a population. The ability to express two alleles simultaneously is a feature of diploid organisms, which have two copies of every gene. Homozygous genotypes can have the same alleles. As an alternative, a heterozygous genotype can be formed by mixing alleles of various kinds. Only one copy of a gene is present in haploid organisms and cells, although the population as a whole can have a large number of alleles.