MCAT Content / Mendelian Concepts / Phenotype And Genotype

Phenotype and genotype

Topic: Mendelian Concepts

An organism’s phenotype is an observable characteristic, while genotype is its specific genetic information.

Mendel’s experiment of observing the characteristics of the true-breeding pea plants led him to discover its appearance or phenotypes and developed genotypes for those traits. Consequently, after cross-breeding two plants, he noticed that one form of the trait was “dominant” over another so it masked the presence of the other “recessive” form. Even if the phenotype or visible form is hidden, the genotype or the allele controlling that form of the trait can still be passed on to the next generation and produce the recessive form in the second generation.

Appearance and genetic makeup of garden pea plant flowers: Based on Mendel’s experiments, the genotype of the pea flowers could be determined from the phenotypes of the flowers. In this image, the B represents the dominant allele and the b represents the recessive allele. Genotypes come in pairs due to the genetic information passed from parents.

Practice Questions



Khan Academy


MCAT Official Prep (AAMC)

Biology Question Pack, Vol. 1 Question 19

Sample Test B/B Section Passage 7 Question 37

Practice Exam 1 B/B Section Passage 1 Question 1

Practice Exam 1 B/B Section Question 58


Key Points

• Based on Mendel’s experiments with the garden peas, one phenotype was always dominant over another recessive phenotype for the same trait; even if the phenotype (observable characteristic) is hidden, the genotype (specific genetic information) can still be passed on to next generation and produce the recessive form in the second generation.

Key Terms

phenotype: the observable characteristics of an organism, often resulting from its genetic information or a combination of genetic information and environmental factors

genotype: the specific genetic information of a cell or organism, usually a description of the allele or alleles relating to a specific gene.

recessive: able to be covered up by a dominant trait

dominant: a relationship between alleles of a gene, in which one allele masks the expression (phenotype) of another allele at the same locus

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