Essay on Main Classes in which the Genetic Disorders are Classified !
Changes may occur in the composition of one or more genes on a chromosome due to mainly the effect of mutagenic agents.
Image Source: nashuafibrosupport.files.wordpress.com
ADVERTISEMENTS:
The mutant genes, particularly on transmission from the parents to the offspring, may produce structural, physiological or biochemical abnormalities. Even a chromosome may undergo fragmentation leading to partial or complete loss of its genes. There are various other reasons which produce genetic disorders in man. These are also known as congenital diseases because these are present & existing from the time of birth. Classification of genetic disorders these may be classified as:
I. Chromosomal abnormalities:
These are deviations from the normal chromosome number or structure. Examples include Down’s syndrome and Turner’s syndrome.
II. Incompatibility of genes:
Disorders of incompatibility of gene are of two types –
(a) Rh factor incompatibility leads to erythroblastosis foetalis (a hemolytic disorder) during pregnancy.
ADVERTISEMENTS:
(b) ABO incompatibility may lead to hemolytic disorder of new born characterised with anaemia & jaundice. It is less severe as compared to Rh-incompatibility. It occurs even in first baby.
III. Single gene disorders (Mendelian or monogenic):
These are conditions that are produced by the effects of one gene or a gene pair. Such traits are usually transmitted in simple patterns as originally described by Gregor Mendel.
(a) Autosomal dominant traits are transmitted on the autosomes (i.e., chromosomes other than the X or Y) and are expressed when only a single copy of the mutant gene is present. Huntington disease is an example of an autosomal dominant disorder.
(b) Autosomal recessive traits are transmitted on the autosomes and are expressed only when both copies of a gene are mutant. Cystic fibrosis is an autosomal recessive disorder.
ADVERTISEMENTS:
(c) X-linked traits are transmitted on the X chromosome. An example of an X-linked disorder is Duchenne-type muscular dystrophy.
IV. Multifactorial traits:
Result from the combined effects of multiple genetic and non-genetic influences. Examples include common kind of cancer and atherosclerotic heart diseases and diabetes etc.