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Multiple Alleles, the Inheritance of Sex Chromosomes

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The human body has three billion pair of DNA, 28000-34000 pairs of genes and 23 pairs of chromosomes. This translates into a myriad sequence which could explain the wide scope of genes. Genes are the basic and structural and functional units of genetics; therefore the basic unit of inheritance that is composed of DNA and RNA.   They control the cells by directing the formation of proteins. An allele is an alternative form of a gene and it represents the different version of a similar gene (Pollard and Earnshow, 2007).

A gene is comprised of two alleles and each individual carries only two alleles of each gene, which exhibit a dominant recessive relationship. The dominant allele will prevail over the recessive gene and is responsible for the resulting phenotype. Recessive alleles will, therefore, not affect the phenotype of the individual. A pair of allele resulting from the various combinations of alleles can be referred to as the genotype while the resulting physical trait as a result of the genotype is called the phenotype (Pollard and Earnshow, 2007). Multiple alleles arise where there are three or more different alleles of a particular gene in a gene pool.

This results in polymorphism where two or more phenotypes exist in a given population (Pollard and Earnshow, 2007). The occurrence of multiple alleles can be attributed to the difference in the non-coding DNA found between genes rather than the DNA sequence variation. Inheritance is, therefore, based on a non-mendelian pattern. An example is the ABO blood group and the coat colour of many species. The ABO blood group phenotype is determined by three alleles, IA, IB, and IO (Pollard and Earnshow, 2007).

Bearing in mind that each individual organism will possess only two alleles with one allele being from each parent, three multiple alleles will, therefore, result in six possible genotypes. A homozygous individual will possess identical alleles while a heterozygous individual will possess different alleles (Pollard and Earnshow, 2007).

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