The genetic makeup of an organism is called its genotype and its observable traits are its phenotype. In other words, what a person looks like is the result of his or her DNA. A great example that explains this concept is Gregor Mendel’s experiments with true-breeding yellow and green pea plants (P1). The phenotype of the plants is their color, yellow and green. When Mendel crossed these two plants, all the offspring (F1) were yellow. But the green color was not lost as it showed up again in the next generation (F2). Mendel didn’t know it at the time, but the underlying genotypes of the green and yellow plants were responsible for the traits seen in the F1 generation.

Both the green and yellow P1 pea plants had identical alleles for the gene that controls their color, meaning they were homozygous. When two green or two yellow plants were bred together, all the offspring of the green plants were green, and all the offspring of the yellow plants were yellow. However, when a green plant was crossed with a yellow plant, all the F1 offspring were yellow. This is because the F1 generation was heterozygous for the color trait, meaning they had different alleles for color. And, of the two alleles for the color gene, yellow was dominant making all the F1 plants yellow. The pea plant alleles in F2 would have to be homozygous recessive for the plant to be green

Comparison Chart

Genotype Phenotype
The observable traits of an organism? No Yes
The genetic makeup of an organism? Yes No
How is it observed? DNA sequencing, PCR assay, if needed (see image below) By looking at the organism
Refers to the information coded on alleles Yes No
Examples include hair color, eye color, height No Yes
Is it inherited? Partially, one allele from each parent No
What does it contain (show)? All heredity information for the organism even genes that are unexpressed. Only the genes that are expressed.

Polymerase chain reaction
The image above shows how the polymerase chain reaction (PCR) assay works to amplify small samples of DNA for genetic analysis. Genetic analysis reveals a person’s genotype which codes for their observable characteristics, aka their phenotype.


  • Genotype vs Phenotype. (n.d.). In Retrieved from
  • OpenStax. (May 20, 2013). Mendel’s Experiments in Heredity. In Biology. (Chapter 12). Retrieved from