Pseudodominance

Pseudodominance is a genetic phenomenon that occurs when a normally recessive trait is expressed in the phenotype due to the absence of a dominant allele. This can occur due to a deletion of a section of a chromosome that contains the dominant allele, or due to the inheritance of a single chromosome from one parent (uniparental disomy).

Mechanism

Pseudodominance occurs when a normally recessive trait is expressed in the phenotype due to the absence of a dominant allele. This can occur due to a deletion of a section of a chromosome that contains the dominant allele, or due to the inheritance of a single chromosome from one parent (uniparental disomy).

In the case of a deletion, the individual will have only one copy of the gene in question, and if this copy carries the recessive allele, the recessive trait will be expressed. This is because there is no dominant allele present to mask the expression of the recessive trait.

In the case of uniparental disomy, the individual inherits both copies of a chromosome from one parent, and none from the other. If the parent from whom the chromosomes are inherited carries two copies of the recessive allele, the individual will express the recessive trait.

Examples

Pseudodominance has been observed in a number of genetic disorders, including Huntington's disease, Cystic fibrosis, and Tay-Sachs disease. In these cases, the individual expresses the disease phenotype even though they have only one copy of the disease-causing allele, due to the absence of a healthy allele.

See also

• Dominance (genetics)
• Recessive trait
• Uniparental disomy
• Deletion (genetics)

References

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