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.

The genotype describes the genetic makeup or alleles of the individual, while the phenotype describes the physical characteristic of the individual.

The parent generation refers to the generation in which the two organisms are crossed; the F1 generation is the first filial generation, or the offspring produced from the cross; the F2 generation is the second filial generation, or the offspring produced from a cross between two F1 organisms.

When attempting to determine if an organism is heterozygous or homozygous for a dominant trait, it is best to use a test cross. A test cross involves crossing the flower in question with a homozygous recessive flower. Since a white flower can only contribute a white allele, we can determine if the purple flower in question is heterozygous or homozygous. Any white flowers in the next generation will confirm that the purple flower is heterozygous. If they are all purple, we can confirm that the flower is homozygous for the trait.