13. Which of the following genetic or chromosomal abnormalities is correctly described?

A. In Tay-Sachs disease, the body starts producing abnormally shaped red blood cells.
B. In phenylketonuria, the body is unable to produce a critical enzyme, which results in an accumulation of poisons that causes profound intellectual disabilities.
C. In sickle-cell anemia, the child receives an extra chromosome during conception and, as a result, develops severe mental disabilities.
D. In Down syndrome, the brain tissues of the cortex degenerate, resulting in death.

Tay-Sachs disease is a genetic disorder that is fatal in its most common variant, known as Infantile Tay-Sachs disease. It results from the accumulation of harmful quantities of fat in the nerve cells of the brain due to mutations in the HEXA gene. This leads to progressive damage to the cells and a decrease in cognitive and physical development, typically resulting in death by age five.

Phenylketonuria (PKU) is a metabolic disorder where the individual cannot metabolize phenylalanine, causing intellectual deficits if left untreated. It is easily detected and treated with a special diet to prevent intellectual disabilities.

Sickle-cell anemia is caused by a genetic mutation affecting the shape of red blood cells. It results in sickle-shaped blood cells that impede oxygen transport and can lead to various complications.

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