Mendel’s approach to answering scientific questions was highly focused. He chose just a handful of traits to study, seven to be exact, and by doing so was able to more easily keep an accurate mathematical record of each of the traits and how they carried to subsequent generations. The approach that he took, looking at a lesser quantity of traits, gave him an advantage because he was able to realize a higher quality of information from his research.
The simplicity of it gave him more control over the traits of the subjects, the garden peas, by giving him control over which parents were involved in the mating process. Some of the advantages that Mendel had in choosing to study the garden pea plant are the rate at which the plant grows and reproduces gives it a short life cycle, making it easy to collect a lot of data in a relatively short amount of time. Also, they are easy to grow and to cross pollinate. Hereditary characteristics are passed from generation to generation through genes, sometimes skipping one or more generations.
Each gene has a set of traits, called alleles that dictate which characteristic that individual will have. Every trait of someone, in humans, from eye color and nose size to overall height and ability to wiggle one’s ears, is determined by which alleles that particular gene has, and which of those alleles is the dominate one. So, the genes that dictate nose size and shape may have, for example, an allele for Mom’s little button-like nose or for Dad’s big, ski-slope nose.
Or, it could have one that matches the nose of Great Grandpa Henry! Each of us carries two alleles, or traits, for every gene. Sometimes they are identical, for example a person could have two alleles for thick eyebrows, and will have thick eyebrows as a result. Or they could have two for sparse eyebrows, giving them sparse eyebrows. Individuals with two matching alleles for a particular trait are said to be homozygous for that trait. Sometimes the alleles are not identical and are then considered heterozygous.
In those that are heterozygous for the eyebrow trait, there could be one allele that produces thick eyebrows and one that produces sparse eyebrows. When someone has alleles that differ for a particular trait, as in with the example above, only one of the alleles can be expressed. The dominate allele is triumphant and the recessive alleles is masked. Because of this, simply observing someone’s phenotype, the traits that are expressed in an individual, will not reveal the full complement of alleles that the individual carries, also called their genotype.