Notes on Single-Gene Disorders

Rahul's Noteblog Notes on Genetics Notes on Single-Gene Disorders

Variable Expression:

• Variability in degree of phenotypic expression.

• Influenced by environment, allelic heterogeneity, heteroplasmy, and modifier loci.

Incomplete Penetrance:

• Individuals have disease genotype, but don't display genotype.

• There is no expression at all, unlike in variable expression.

Pleiotropy:

• Single mutation affects multiple organs.

Locus Heterogeneity:

• Same disease phenotype but mutations in different loci.

Anticipation:

• Individuals in recent generations develop increased severity and earlier onset of symptoms compared to individuals of earlier generations.

• Eg., diseases associated with abnormal triplet repeat expansions.

Imprinting:

• One allele is activated and the other is rendered inactive.

• Sometimes, the supposedly active allele is deleted or mutated, while the other allele is still normally inactivated.

Prader-Willi Syndrome:

• Deleted or mutated locus is at 15q11-13 (paternal).

Angelman Syndrome:

• Deleted or mutated locus is at 15q11-13 (maternal).

Additional Readings:

Basic Genetics

1. Single-Gene Disorders
2. Population Genetics
3. Genetic Disease Transmission Probability
4. What is Cytogenetics?
5. Notes on Bloom's Syndrome
6. Introduction to Human Chromosomes
7. Life Cycle of Somatic Cells

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