Mendelian Disorders
Read the following passage carefully and answer the given questions.
Genetic disorders may be grouped into two categories – Mendelian disorders and Chromosomal disorders. Mendelian disorders are mainly determined by alteration or mutation in a single gene. These disorders are transmitted to the offspring on the same lines as in the principle of inheritance. The pattern of inheritance of such Mendelian disorders can be traced in a family by pedigree analysis. Most common and prevalent Mendelian disorders are Haemophilia, Cystic fibrosis, Sickle-cell anaemia, Colour blindness, Phenylketonuria, Thalassemia, etc. The Mendelian disorders may be dominant or recessive. By pedigree analysis, one can easily understand whether the trait in question is dominant or recessive. Similarly, the trait may also be linked to the sex chromosome or an autosome.
Which one of the followings is an example of an inborn error of metabolism and inherited as autosomal recessive trait?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Phenylketonuria
Mendelian disorders are caused by a change in a single gene, and they are passed on by the usual rules of inheritance. A disorder may be dominant or recessive, and its gene may lie on an autosome or on the sex chromosome. An inborn error of metabolism is a disorder in which the body lacks one enzyme. In phenylketonuria the enzyme that changes the amino acid phenylalanine into tyrosine is missing, so phenylalanine builds up and harms the brain. It is inherited as an autosomal recessive trait.
(1) Phenylketonuria — Correct. It is an inborn error of metabolism and an autosomal recessive trait.
(2) Thalassemia — Incorrect. It is also an autosome-linked recessive disease, but it is a blood disorder in which too few globin chains are made. It is not named as an inborn error of metabolism.
(3) Haemophilia — Incorrect. It is a sex-linked recessive disease. Its gene lies on the X chromosome.
(4) Colour blindness — Incorrect. It is a sex-linked recessive disorder. Its gene also lies on the X chromosome.
Note: The passage is taken from NCERT. NTA has put lines of the NCERT text together to make it. Most CUET (UG) questions come straight from NCERT, so study the book line by line, including figures and their titles.
NCERT Extract:
Mendelian Disorders – …
