CHROMOSOME ABNORMALITIES

OAC Biology

Inheritance of genetic information is remarkably accurate since most genes pass through countless generations unchanged. However, sometimes there is a change in the genetic information. The change is called a MUTATION. Sometimes the movement of chromosomes during meiosis goes awry. When this happens, a gamete may end up with an unusual number of chromosomes. If this gamete fuses with another gamete during fertilization, the new organism will also carry an unusual number of chromosomes and a serious genetic condition may result.

When homologous chromosomes fail to separate properly during meiosis the condition is known as NON-DISJUNCTION. The chances of non-disjunction increases with age, hence, older women are more likely to produce children with a genetic condition (such as DOWN'S syndrome) than younger women.

REVIEW QUESTIONS:

#2. What is non-disjunction?

a sample of amniotic fluid is taken from the pregnant woman and a karyotype (or wide-variety of other tests) is performed on the fetal cells found in this fluid

a process called AMNIOCENTSIS allows a sample of fetal cells for chromosome analysis to be obtained

this test is performed during the 14 – 16^th week of pregnancy

amniocentesis is carried out in conjunction with ULTRASOUND (looking at the fetus on a monitor) in order not to accidentally injure the fetus with the hypodermic needle

this type of diagnosis is useful in the detection of genetic disorders if biochemical origin

PKU is a disease caused by the inability of the body to produce a specific enzyme required to break down a protein in itself

All newborns are screened (blood test) for PKU

If the baby has PKU and is not screened, mental retardation can result

If the baby has PKU and is screened, the baby will be put on a special diet for the first few years of life and will develop normally

Cystic fibrosis can be detected by various blood tests and the child could then receive immediate medical attention in order to extend their life expectancy

E-mail Mr. Galajda at:  david.galajda@sac.on.ca