Genetic Disorder
A genetic disorder is a disease or condition caused by an abnormality in an individual's genome, which may involve a mutation in a single gene (monogenic), multiple genes (polygenic/multifactorial), or chromosomal abnormalities. Genetic disorders can be inherited from parents (hereditary) or arise as new mutations (de novo). They range widely in severity — from manageable conditions like colour blindness to life-threatening diseases like Huntington's disease — and understanding their genetic basis is crucial for diagnosis, treatment, and genetic counselling.
Examples of Genetic Disorders and Their Inheritance Patterns
| Disorder | Inheritance Pattern | Gene / Chromosome | Key Feature |
|---|---|---|---|
| Cystic fibrosis | Autosomal recessive | CFTR gene, chr 7 | Thick mucus in lungs and gut |
| Sickle cell anaemia | Autosomal recessive | HBB gene, chr 11 | Abnormal haemoglobin (HbS) |
| Huntington's disease | Autosomal dominant | HTT gene, chr 4 | Progressive neurodegeneration |
| Down syndrome | Chromosomal (trisomy) | Chromosome 21 | Intellectual disability, distinct features |
| Haemophilia A | X-linked recessive | F8 gene, X chromosome | Impaired blood clotting |
| Colour blindness | X-linked recessive | OPN1LW/OPN1MW, X chr | Cannot distinguish red/green |
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Related Terms
Genetic Mutation
A genetic mutation is a permanent alteration in the nucleotide sequence of an organism's DNA, which may affect one or more genes. Mutations can arise spontaneously during DNA replication, or be induced by mutagens such as radiation, chemicals, or viruses. While many mutations are neutral or harmful, some confer advantages that can be selected for during evolution, making mutations the ultimate source of genetic variation in populations.
Recessive Allele
A recessive allele is a version of a gene whose trait is expressed in the phenotype only when two copies of it are present (i.e., in the homozygous state), because it is masked by a dominant allele when paired with one. Recessive alleles are conventionally represented by lowercase letters (e.g., "b" for blue eye colour). Many genetic disorders, such as cystic fibrosis and sickle cell anaemia, are caused by recessive alleles.
Phenotype
The phenotype is the observable set of physical and biochemical characteristics of an organism, resulting from the interaction of its genotype with the environment. It encompasses all visible traits such as eye colour, height, blood type, and behavioural tendencies. Understanding phenotype is fundamental to genetics because it reveals how genetic information is expressed in living organisms.
"Genetic" derives from Greek "genetikos" (relating to birth or origin), from "genesis" (origin). "Disorder" comes from Old French "desordre" meaning "lack of order". Together the term denotes a disruption of normal biological function originating in the genetic material.