Alleles

 

Allele

An allele is a variant form of a gene. Some genes have a variety of different forms, which are located at the same position, or genetic locus, on a chromosome. Humans are called diploid organisms because they have two alleles at each genetic locus, with one allele inherited from each parent. Each pair of alleles represents the genotype of a specific gene. Genotypes are described as homologous if there are two identical alleles at a particular locus and as heterogeneous if the two alleles differ. Alleles contribute to the organism's phenotype, which is the outward appearance of the organism.

Some alleles are dominant or recessive. When an organism is heterozygous at a specific locus and carries one dominant and one recessive allele, the organism will express the dominant phenotype. Alleles can also refer to minor DNA sequence variations between alleles that do not necessarily influence the gene's phenotype.

Dominant allele 

   This is a gene that is always expressed it overshadows every other character even when it is paired with recessive allele. It is always represented with a uppercase letter , for instance the allele responsible tallness is represented with -T.

 

Recessive allele

  This is a gene that is not expressed when paired with a dominant allele. However, its really noticeable when paired with another recessive allele and is represented with lowercase letter - tt for shortness.