Genetics - the Biology of Inheritance

A disease caused by any abnormality in a person'sComplex disease is the most common type of
genes or chromosomes is called a genetic disorder.genetic disorder. In these disorders, gene mutation
Several diseases have a genetic side to them.does not cause the disease, just increases the
Some genetic disorders are inherited. Since you inheritpredisposition to the disease. Heart disease, obesity
genes from your parents, you may also inherit anyand Alzheimer's disease are examples of complex
abnormality in the gene. That is one of the tenets ofdisease. Chromosomal disorders occur because of
genetics, the branch of biology associated with theabnormalities in the structure or number of
study of genes and their effects. A gene that haschromosomes. Down's syndrome and Klinefelters
undergone a mutation (alteration) is passed downsyndrome are prime examples of these disorders.
through a family and the genetic disorder caused byDown's syndrome, also referred to as Trisomy 21, is
the mutated gene can affect children of all thea genetic disorder caused by the presence of an
subsequent generations. These mutations, orextra 21st chromosome. The effect of the extra
alterations, in genes can occur due to exposure to21st chromosome varies greatly, depending on
environmental toxins or may occur randomly. Geneticwhether the extra strand is present is full or parts,
disorders are also caused by abnormalities in thegenetic history, and pure chance. Down's syndrome is
structure and function of chromosomes. It ischaracterized by some abnormality of cognitive
imperative to note that not all genetic disorders areability, physical growth, and facial appearance. Some
inherited. Some, like Down's syndrome, occur asof the common physical features of a person with
isolated random incidents.Down's Syndrome include a single transverse palmar
Genetic disorders account for a large number ofcrease, instead of two, an almond shape to the
diseases, and can present in various ways. The mosteyes, shorter limbs, poor muscle tone, a larger than
widely known genetic disorders are Down'snormal space between the big and second toes, and
syndrome, Klinefelter's syndrome, sickle cell anemiaa protruding tongue. Individuals with Down's
and spina bifida. Genetic disorders can often be lethalsyndrome also have specific health concerns such as
or may sometimes cause conditions that need aa higher risk for congenital heart defects, recurrent
significant medical attention. More than 6000 geneticear infections, and thyroid dysfunctions.
disorders have been identified till date.Klinefelter's syndrome is caused by the presence of
Genetic Disorders can be classified asan extra X sex chromosome. The main result is the
* Single gene disorderspresence of small testes and reduced fertility. Other
* Complex diseasephysical and behavioral problems are common, though
* Chromosomal disordersthe severity varies. It is the second most common
Single gene disorders occur because of one defectiveextra chromosomal disorder.
gene. These disorders are uncommon and the biologyThe biology behind genes and chromosomes and
behind them is not fully understood. Examples of thispatterns of inheritance is yet to be completely
type of genetic disorder include muscular dystrophydeciphered. Genetics throws up interesting mysteries
and cystic fibrosis.every now and then.