7. The childhood form of amaurotic family idiocy ( Tay-Sachs) is inherited as an autosomal recessive trait and usually ends in death by 4-5 years. The first child in the family died from the analyzed disease, at the same time, the second child should be born. What is the probability that the second child will suffer from the same disease?
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Answer:
term for Tay-Sachs disease (TSD) which is concisely defined by OMIM (Online Mendelian Inheritance in Man) as "an autosomal recessive, progressive neurodegenerative disorder, which in the classic infantile form, is usually fatal by age 2 or 3 years, results from deficiency of the enzyme hexosaminidase A. " "Autosomal" points to the gene for TSD residing on a nonsex (autosomal) chromosome (namely, chromosome15q23-q24). "Recessive" indicates a person with 2 copies of the gene has TSD whereas someone with 1 copy is a carrier in normal health. TSD worsens, with time, as the central nervous system progressively deteriorates. The "classic" ("textbook") type of TSD has its insidious onset in infancy. The child with TSD usually develops normally for the first few months of life. An exaggerated startle reaction may first be noted.