Mendel did not know about chromosomes or meiosis, but from his careful analysis of stem length and flower color in peas, he was able to infer the existence and behavior of factors now called genes - tiny objects he would never see. By demystifying how alleles pass intact through a hybrid, he gave evolutionary theorists the kind of mechanism they needed to explain the origins and maintenance of biological diversity. Research has shown that many of the observable traits we have discussed are caused by some chemical in the organism's body. Genes control these chemical differences. Thousands of base pairs long.
Different alleles have different sequences of nucleic acid bases.
The allele that is expressed in the heterozygous condition. The allele that is masked in the heterozygous condition. Recessive allele is ONLY expressed in the homozygous condition, e.g. bb, tt, etc. Designated by pairs of letters, e.g., AA, Aa, aa. An ee individual produces only gametes that are e For two genes, the task of determining the gametes is a bit trickier.