The human genome consists of 46 chromosomes, specifically 44 autosomal chromosomes, similar in both males and females, and 2 gender specific sex chromosomes (X and Y). It has been known for many years, based on Mendel's pea experiments, that DNA recieved from both parents can be variably expressed to produce offspring with different characteristics, but how does this occur?
DNA is the chemical sequence that encodes the production of all bodily proteins, from enzymes in our stomach to keratin in our hair. Genes are specific sequences of DNA which determine certain features such as eye colour, with alleles being different forms of these genes. A child inherits alleles from both parents and so may inherit the allele for blue eyes from their mother and the allele for brown eyes from their father. Which allele is expressed depends on the dominance of the gene, meiosis and mutation. Mutations may occur either at the level of DNA e.g. substitutions or deletions of bases, or at the chromosomal level, e.g. issues of assortment, structure or number of chromosomes. Therefore our phenotype is the combined result of which alleles we inherit and the form in which the DNA persists.