Genetic_Disorders

Genetic Disorders Each year a number of children are born with biological defects that impair normal function. One lethal disorder inherited as a recessive allele is Tay-Sachs disease. This is caused by a dysfunctional enzyme that fails to break down brain lipids of a certain class. The symptoms usually become manifest a few months after birth. Some symptoms are seizures, blindness and degeneration of motor and mental performance. Death is the final result of this disease in children. With Tay-Sachs disease, the brain cells of a baby are unable to metabolize gangliosides, a type of lipid, because a crucial enzyme does not work properly. As the lipids accumulate in the brain, the brain cells gradually cease to function normally. Only children who inherit two copies of the Tay-Sachs allele qualifies as a recessive. At the biochemical level, we observe an intermediate phenotype characteristic of incomplete dominance: The enzyme deficiency that causes Tay Sachs disease can be detected in heterozygotes, who have an activity level of the lipid-metabolizing enzyme that is intermediate between individuals homozygous for the normal allele and individuals with Tay-Sachs disease. Heterozygotes lack symptoms of the disease, apparently because half the normal amount of functional enzyme is sufficient to prevent lipid accumulation in the brain. In fact, heterozygous individuals disease, cells, allele, sickle-cell, normal, enzyme, brain, syndrome, symptoms, tay-sachs, one, level, individuals, chromosome, blood, two, result, off, heterozygotes, gamete, during, children, women, type, trisomic, suffer, red, receives, properly, phenotype, oxygen, nondisjunction, molecular, mental, meiosis, lipids