4 Chap 4 Congenital heredity

Mosaicism DOES NOT results from chromosome nondisjunction occurring in the ovum before fertilization.
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Mosaicism DOES NOT results from chromosome nondisjunction occurring in the ovum before fertilization.
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The presence of an extra chromosome in a cell is called a __________.
trisomy
The gene responsible for the fragile X syndrome is __________.
FMR1
Name four major factors known to induce congenital malformations.
1. Chromosomal abnormalities
2. Abnormalities of individual genes
3. Intrauterine injury to the embryo or fetus by drugs, radiation, maternal infection, or other harmful environmental factors
4. Environmental factors acting on a genetically predisposed embryo
What are three conditions that may result in Down syndrome?
1. Nondisjunction during gametogenesis, leading to the formation of an abnormal gamete containing an extra chromosome 21
2. An extra chromosome 21, acquired as part of a translocation chromosome
3. Nondisjunction occurring in the zygote.
Some infections acquired by a pregnant woman may injure the developing fetus. Name three infectious agents that are known causes of congenital malformations.
Rubella (the virus of German measles),

cytomegalovirus (the virus of cytomegalic inclusion disease),

and toxoplasma gondii (the protozoan parasite)
What are three methods a doctor might use to identify congenital abnormalities in the fetus?
Tests on maternal blood; examination of amniotic fluid; examination of fetal cells; utrasound examination of the fetus
What is the preferred diagnostic method for fragile X mental retardation?
DNA analysis
Name two disadvantages of chorionic villi sampling
More technically difficult to perform; may lead to spontaneous abortion and limb deformities
Compare and contrast amniocentesis versus chorionic villi sampling.
Both are used to obtain fetal cells for evaluation; the fetal cells are grown in the lab by tissue culture techniques and later used to determine the karyotype of cells. The karyotype will help determine abnormalities in chromosomal number or structure. Analysis of the fetal DNA will help determine presence of genetic diseases.

Amniocentesis examines amnionic fluid obtained anytime between the 14th to 18th week of pregnancy.

Chorionic villi sampling examines fetal cells obtained without extracting amnionic fluid during the 8th to 10th week of pregnancy; it involves less risk, with results obtained earlier, but is more technically difficult to perform and may lead to spontaneous abortion and limb deformities.