Головна

Relationship between age of mother Risk of a Trisomy -21 in child

  1. Are video games bad for children?
  2. Childhood diseases
  3. Common Motherboard Items
  4. Connection between identity and language
  5. Differences in teaching children and adults
  6. Differences in the transfer of information between languages . (Differences in relationships between concepts.)

Age of motherRisk of Trisomy -21 in child, %

16-26 77/10000

27-34 4/10000

35-39 29/10000

40-44 100/10000

45-47 333/10000

All mothers combined 15/10000

In about 95 % of the cases of Down syndrome the cause of the genetic abnormality is nondisjunction of chromosome 21. This results in an extra chromosome 21 in the cells of the defective child. Down syndrome may also be the result of an abnormality, known as a translocation, in the chromosomes of one of the parents.

Translocation occurs when a portion of a chromosome is broken off and becomes attached to another chromosome. The patient with translocation mongolism usually has a third chromosome 21 attached to a larger chromosome, such as 15.

When cases of Down syndrome due to translocation are studied, it is usually found that one parent phenotypically normal, has only 45 separate chromosomes - one chromosome being composed of most of chromosomes 15 and 21 joined together.

Trisomy - 13 produces Patau syndrome. About 2 in 10.000 live births produce individuals with trisomy-13. Characteristics of individuals with trisomy-13 include cleft lip and palate, small eyes, polydactyly (extra fingers and toes), mental and developmental retardation, and cardiac anomalies, among many other abnormalities. Most die before the age of three months.

Trisomy-18 produces Edwards syndrome. It occur in about 2.5 in 10.000 live births. For reasons that are not known, about 80 percent of Edwards syndrome infants are female. Individuals with trisomy-18 a small at birth and have multiple congenital malformations affecting almost every organ system in the body. Clenched fists, elongated skull, low-set malformed ears, mental and developmental retardation, and many other abnormalities are associated with the syndrome. Ninety percent (90%) of infants with trisomy-18 die within six months, often from cardiac problems.

One human disorder cased by a heterozygous deletion is Cri-du-chat syndrome which results from an observable deletion of part of the short arm of chromosome 5, one of the larger human chromosomes. Children with cri-du-chat syndrome are severely mentally retarded, have a number of physical abnormalities, and cry with a sound like the mew of a cat (hence the name, which is French for "cry of the cat").

Another example is Prader-Willi syndrome, which results from heterozygosity for a deletion of part of the long arm of chromosome 15. Infants with this syndrome are weak because their sucking reflex is poor, making feeding difficult. As a result, growth is poor. Other phenotypes associated with the syndrome include poor sexual development in males, behavioral problems, and mental retardation. Many individual with the syndrome go undiagnosed, so its frequency of occurrence is not known.

Molecular genetics is a specific relationship between genes and enzymes, historically embodied in Beadle and Tatum's "one gene - one enzyme" hypothesis, which states that each gene controls the synthesis or activity of a single enzyme. Since we know that enzymes may consist of more than one polypeptide and that genes code for individual polypeptide chains, a more modern title for this hypotheses is " one gene-one polypeptide".

Gene diseases (metabolism errors)

Many human genetic diseases are caused by deficiencies in enzyme activities. Most of these diseases are inherited as recessive traits.



Autosomal abnormalities | A) hereditary defects of amino acid metabolism
© 2016-2022  um.co.ua - учбові матеріали та реферати