Genetics - Part 3 - Human Genetics Introduction This chapter is a review of patterns of inheritance in humans including a review of genetic diseases. The genetic diseases are divided into two categories: chromosomal abnormalities and gene abnormalities. Chromosomal abnormalities are caused by cells that have extra or missing chromosomes or parts of chromosomes. Gene abnormalities (gene mutations) occur when the genetic instructions stored in the DNA are altered so that the protein product coded for by the gene is less functional or nonfunctional. Prenatal Diagnosis The techniques listed below enable physicians to diagnose many kinds of genetic abnormalities by examining some of the cells from the developing fetus. Amniocentesis The fetus is surrounded by a layer of liquid called amniotic fluid. Amniocentesis is a technique in which a sample of amniotic fluid is removed and cells that it contains are grown on a culture dish. Because these cells are of fetal origin, any chromosomal abnormalities present in the fetus
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