GENOTYPE VS. PHENOTYPE

=Genotype vs. Phenotype= Letters are commonly used to represent different versions of a gene (alleles). For instance in the example below the letter 'A' represents an allele that codes for red feathers. The letter 'a' represents an allele that codes for blue feathers. The same letter has been used to show that they are in fact just slightly different forms of the gene for feather colour. Organisms that reproduce sexually normally have two alleles (versions) of each gene -one that was inherited from the organisms mother and one from their father. However, this means that there are three possible combinations of alleles… [image:http://i.imgur.com/VC7TThK.png] '''Genotype''' The combination of alleles an individual possesses (e.g. Aa) is known as their genotype. If an individual has two of the same alleles, they are said to be homozygous. If they have two different alleles they are said to be heterozygous. '''Phenotype''' An individual's phenotype is its observable characteristics or traits (e.g. red feathers) ==Dominant & Recessive Alleles== You may have noticed that there are three possible genotypes (AA, Aa, aa) and only two different possible phenotypes (red or blue). One allele is usually dominant. A dominant allele is a version of a gene that is '''expressed''' and gives the individual its characteristic even in the presence of an alternate form of the gene (allele). The other allele is usually recessive which means it is only expressed if there are no alternate forms of the gene (other alleles) present. Therefore, both the genotypes AA and Aa produce a red feather phenotype.