CHROMOSOMAL ABNORMALITES

These are abnomalities which occur in genes and chromosomes.These results in serious developmental problems.Most chromosomal defects are the result of mistakes during meiosis when the ovum & sperm are formed.
A chromosome pair may not separate properly, or part of a chromosome may break off.

Down Syndrome (Autosomal Abnormality)

It is named after the British physician Langdon Down who ist notwd in 1866. In 1959 the French geneticists Jerome Lejeune and his colleagues identifies its genetic basis.Its the most common chromosomal abnormality. Autosomes are all chromosomes other than sex chromosomaes. There are 22 pairs of autosomes. The 23rd pair is the sex chromosome. Down syndrome is genetically transmitted form of mental retardation caused by the presence of an extra chromosome. in most cases, it results from the faliure of the 21st pair of chromosome to separate during meiosis, so the new individual inherits 3 of these chromosomes rather than the normal two. So it is called Trisomy 21.

In other frequent forms, an extra broken piece of a 21st chromosome is present. The reason for the presence of the extra chromosome is not known. But the health of the sperm & ovum is involved. Geneticists believe that the ova which is present at the time of birth weakens over time. Women between 18 & 38 years of age are less likely to give birth to children with Down Syndrome.
Like older mothers, older fathers are also more likely to have children with this disorder. Children with down syndrome have distinct physical features- a short, stocky build, a flattened face, a protruding tongue, almond shaped eyes, & an unusual crease running across the palm of the hand.
Such infants are born with eye cataracts and heart and intestinal defects. Because of medical advances, fewer down syndrome children die early than was the case in the past, but early death is still common. Mortality after 40 is high.
The behavioral consequences of Down Syndrome include mental retardation, speech problems, limited vocabulary, & slow motor development. These problems become more evident with age, since Down Syndrome children show a gradual slowing in development from infancy onward when compared to normal children. Most fall within an IQ range of 20 to 50 & only about 5 percent learn to read. Down Syndrome babies are more difficult to care for than normal infants. Their facial deformities often lead to breathing & feeding difficulties. In addition, they tend to be less emotionally expressive than their normal counterparts They smile less readily, show poor eye contact & explore objects less persistently. Therefore, caregivers need to be more assertive in getting these infants to become engaged in their surroundings. When parents make this effort, their children show better developmental progress.
Early intervention programs for Down Syndrome youngsters also lead to better development, although social, emotional, & motor skills improve more readily than intellectual performance. These findings indicate that even though Down Syndrome is a genetic disorder, environmental factors play an important role in how well these children fare in the long run.


BIBLIOGRAPHY:

Child Develpment- Laura. E. Berk