We can now begin to define a series of important concepts that you should know about genetics.

Phenotype: the physical appearance resulting from the gene pairing.

Genotype: the nature of the pairings.

Gregor Mendel identified two kinds of traits (Dominant and Recessive). These traits are simply different states of a single gene and we call them ALLELES.

Genes occur in pairs along chromosomes. It is important to recognize that you possess genes in pairs. This is precisely what Gregor Mendel saw when he worked with peas. The following illustrates this point for a gene that governs the ability to roll your tongue.

20 People with a RR genotype have 40 gene loci and a total of 40 R genes (2 R's per locus.)

20 People with a heterozygous genotype have 40 gene loci and 20 R genes and 20 r genes.