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.


• Single mutation affects multiple organs.

Locus Heterogeneity:

• Same disease phenotype but mutations in different loci.


• 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.


• 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

Related Topics

1. Genetic and Developmental Disorders
2. Genetic Code, Mutations, and Translation

Random Pages:

The Existence of Matter Body-Mass-Index, Waist-to-Height Ratio, Body Fat, Basal Metabolic Rate Calculator
Video of me playing Hagood Hardy`s "The Homecoming" Notes on Male Reproductive System
Notes on Development of the Breast Notes on Growth Medias and Oxygen Requirements
Notes on Citric Acid Cycle and Glyoxylate Cycle Notes on Correlational Techniques
Differentiation of the Face FAQ on Gastric Digestion
Notes on Basic Gastrointestinal Physiology My Experience during the Iraqi Invasion of Kuwait
Review of Delta Roma Imperiale Fountain Pen What is an ELEK`s Test?
Why did I decide to become a doctor? Medical School Admissions Essay Video: Titanic Piano Theme: The Portrait
Corporate Failure: The Enron Case My Experience during the Iraqi Invasion of Kuwait
USMLE Blood Lab Values Regulation of Heart Rate by Autonomic Nervous System
Images of Antibodies Rahul`s Piano Music MP3 Collection
Notes on Renal/Urinary System Differentiation and Anatomy of a Blastocyst
Notes on Cell Components Notes on Nervous Tissue
Voices from Hell: My Experience in Mussoorie, India Video of Cardiology Examination in a Clinical Setting

Please Do Not Reproduce This Page

This page is written by Rahul Gladwin. Please do not duplicate the contents of this page in whole or part, in any form, without prior written permission.