Molecular Genetics

Heterozygous – Definition and Characteristics

Heterozygous is the state in which an organism has inherited different forms of a particular gene from each one of the biological parents. It certainly holds an important position in molecular biology. Students can learn more about heterozygous and its characteristics here.


Definition and Meaning of Heterozygous

Heterozygous refers to the inheritance of an organism of different forms of a specific gene form both parents. Furthermore, a heterozygous genotype stands in stark contrast to a homozygous one. This is because, in homozygous genotype, an individual inherits identical forms of a particular gene from both the parents.

The representation of a heterozygote is by a capital letter and also a lower case letter. Therefore, its representation takes place as Rr or Ss. Also, a heterozygote for gene R is assumed by experts to be Rr. Here, the capital letter certainly comes first.

A heterozygote advantage refers to a particularly unique situation with the heterozygous genotype. Here the heterozygous genotype involves higher relative fitness than either the homozygous dominant or homozygous recessive genotype. Furthermore, the specific case of heterozygote advantage is because of a single locus. Also, this specific case is overdominance

Complete Dominance

For each trait, diploid organisms have two alleles. Moreover, these alleles are different in heterozygous individuals. Complete dominance inheritance refers to one allele being dominant and the other being recessive. The dominant trait is observed while the recessive trait is masked.

A good example can be round seed shape (R) which is dominant and wrinkled seed shape (r) which certainly is recessive. Furthermore, around seeds plant would have either of the following genotypes: (RR) or (Rr).

Also, a plant with wrinkled seeds would have the genotype: (rr). The genotype (Rr) involves the dominant round seed shape. This is because its recessive allele (r) happens to be masked in the phenotype.

Incomplete Dominance

Here one of the alleles does not mask the other in a complete manner. Rather, one notices a different phenotype which happens to be the combination of the phenotypes of the two alleles.

A suitable example of this is the pink flower color in snapdragons. The expression of the allele that produces red flower color (R) does not take place in a complete manner over the allele that produces white flower color (r). Therefore, the genotype (Rr) is a phenotype that happens to be a mixture of three different colors. Most noteworthy, these colors are red and white, or pink.


Here the expression of the heterozygous alleles in the phenotype takes place in a full manner. An appropriate example of codominance is AB blood type inheritance. The A and B alleles are expressed in a way that is full and equal in the phenotype. Moreover, the experts consider them to be codominant.

Solved Question on Heterozygous

Q1 Which of the following is not a characteristic of Heterozygous?

A. Complete Dominance
B. Incomplete dominance
C. No dominance
D. Codominance

A1 The correct option is C., which is “no dominance.” This is because “no dominance” is not a characteristic of heterozygous. Moreover, the other three options are certain characteristics of heterozygous.

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