The genes controlling traits do not blend during inheritance, but are transmitted as discrete units. Some variation in populations is accounted for by alternate expression of alleles. Chromosomes occur in pairs, with a copy of a given gene on each chromosome. Egg and sperm merge to form a fertilized egg with the full chromosome number. The fertilized egg divides into new cells by mitosis , which maintains the full chromosome number.
Proteins consist of a string of amino acids.
A protein s properties are determined by its amino acid sequence. Mutations alter the base code in an individual s genes and result in altered proteins. If the mutation occurs in a sex cell, it is inheritable. Trait inheritance is due to the chromosomal theory of inheritance. Evolution is gradual.