Question

Hereditary disease in which urine turns black on exposure due to the presence of homogentisic acid is
A. Ketonuria
B. Phenylketonuria
C. Haematuria
D. Alkaptonuria

Answer 1

Genes are the building blocks of heredity. Genes are passed through one generation to another generation (parents to their offsprings). Sometimes, a mutation occurs by the genetic material or genes, so protein cannot work properly and can cause a medical condition named as genetic disorder.

Complete answer:
Mutation is a sudden change in genetic sequence of an individual which may lead to variation of characters.
When the level of ketones in urine is high then ketonuria occurs and this condition is also called ketoaciduria. When fats and proteins are burned then ketones (a type of acid) makes in our body. It is a process that occurs normally but when our health conditions are bad then these ketones are produced in high numbers mainly in diabetic people and pregnant women due to which our blood becomes more acidic and causes health issues.
Phenylketonuria is an inborn metabolism error. The individual lacks an enzyme called phenylalanine hydroxylase. This affects the brain and results in mental disorder.
Blood that we see is called gross hematuria. It produces pink, red, cola colour urine due to the presence of RBCs. It takes a small amount of blood to produce red urine.
Alkaptonuria is an inherited disorder that occurs when our body is not able to produce enough of an enzyme homogentisic dioxygenase because it is used to break down a toxic substance (homogentisic acid). By this acid our bones and cartilage become brittle and our urine turns dark brown or black in colour when exposed to air.

So, the correct answer is “Option D”.

Note:
There are two types of disorders – mendelian disorders and chromosomal disorders.
Mendilian disorder is mainly due to the alteration or mutation in the single gene. Example – haemophilia, etc.
Chromosomal disorder is caused due to absence or excess of one or more chromosomes. Example- turner’s syndrome.