Autosomal recessive

Sickle-cell disease:

It is a hereditary blood disorder, characterized by red blood cells that assume an abnormal, rigid, sickle shape. Sickling decreases the cells' flexibility and results in a risk of various life-threatening complications. This sickling occurs because of a mutation in the haemoglobin gene. Individuals with one copy of the mutant gene display both normal and abnormal haemoglobin. This is an example of codominance. Sickle cell anemia and cystic fibrosis are caused by mutations in single genes, not extra chromosomes so they can not be seen in karyotyping.

The hemoglobin gene in the chromosome 11 is affected by it.

Tay-sachs disease :

It is a rare autosomal recessive genetic disorder. In its most common variant (known as infantile Tay–Sachs disease), it causes a progressive deterioration of nerve cells and of mental and physical abilities that commences around six months of age and usually results in death by the age of four. The disease occurs when harmful quantities of cell membrane components known as gangliosides accumulate in the brain's nerve cells, eventually leading to the premature death of the cells. There is no known cure or treatment.

The HEXA gene is located on the long (q) arm of human chromosome 15, between positions 23 and 24.

The mutation responsible for Tay-Sachs involves a *very* small piece of DNA, too small to be appreciated by karyotype techniques.

It is a genetic disease because the homozygous mutation is documented in 100% of affected children, and carrier (heterozygous) state can be identified in both parents.

We cannot diagnose Tay-sachs on karyotype .

Date: 2014-12-21; view: 1117