Hybridization is the mating of two varieties of a species to produce hybrids. A classic example would be crossing purple flowered pea plants and white flowered pea plants. The resulting offspring would all be genetic hybrids in this case though they may only display one color.   

A genotype is the genetic makeup of alleles coding for a characteristic. In this example, a heterozygote has one recessive and one dominant allele, making the genotype Aa. The phenotype is the observable expression of the genotype. Since a heterozygote has one dominant allele and one recessive allele, the dominant allele is exhibited, thus the phenotype is brown hair.

The phenotype is the observable characteristic of an individual. In this example, a homozygous recessive plant will have a white flower phenotype and a genotype of aa.

An allele is a genetic variant of a given trait. Alleles for the given trait within an individual are located at the same genetic locus. The resulting observable characteristic is called a phenotype. Humans are diploid organisms, meaning that they have two copies of each gene, where each copy may be the same or different alleles.

Gregor Mendel carried out experiments using pea plants to discover the fundamental principles of genetics. Louis Pasteur was a microbiologist who is known for his work with vaccines and pasteurization. Both Francis Crick and James Watson are credited for their discovery of the structure of DNA.

The principle of dominance in genetics states that some alleles are dominant and are expressed instead of the recessive allele. Hybrids are crosses between parents with different traits, and genotypes for different eye colors are different.

The correct code for homozygous dominant is TT. Homozygous means the "same alleles," and the dominant allele is a capital letter, which, in this case is "T."

The correct code for homozygous recessive is tt. Homozygous means the "same alleles," and recessive, in this case, is "t."

When a homozygous tall pea plant and a homozygous short pea plant are crossed, the next generation are all heterozygous and the dominant allele is expressed in all the plants, and the recessive trait seems to disappear. Since we are not told whether the tall or short allele is dominant, we cannot assume either.

Dominant alleles are neither better, nor worse than recessive alleles. They are simply expressed in the phenotype of a heterozygous pair. Several deleterious, and even deadly disorders like Huntington's disease, are inherited via an autosomal dominant pattern.

Note that the frequency of an allele or genotype in a population must be determined experimentally, and can be linked to environmental influences, autosomal versus sex-linked patterns, and numerous other factors.