Read the given passage and answer the following questions.
Mendelian disorders are mainly determined by alteration or mutation in the single gene. These disorders are transmitted to the offspring on the same lines as we have studied in the principle of inheritance. The pattern of inheritance of such Mendelian disorders can be traced in a family by the pedigree analysis. Most common and prevalent Mendelian disorders are Haemophilia, Cystic fibrosis, Sickle cell anaemia, Colour blindness, Phenylketonuria, Thalassemia, etc. It is important to mention here that such Mendelian disorders may be dominant or recessive.
Which of the following is not an autosomal disorder?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Haemophilia
A Mendelian disorder is caused by a change in a single gene. The gene may lie on an autosome (any chromosome other than the sex chromosomes) or on the X chromosome. A disorder whose gene lies on the X chromosome is sex-linked, so it is not an autosomal disorder.
Option (1) Sickle-cell anaemia — An autosomal disorder. Sickle-cell anaemia is an autosome linked recessive trait. A child gets the disease when both parents are carriers of the gene.
Option (2) Haemophilia — Not an autosomal disorder. Haemophilia is a sex linked recessive disease. Its gene lies on the X chromosome, and it passes from an unaffected carrier mother to some of her sons.
Option (3) Phenylketonuria — An autosomal disorder. Phenylketonuria is an inborn error of metabolism inherited as an autosomal recessive trait.
Option (4) Thalassemia — An autosomal disorder. Thalassemia is an autosome-linked recessive blood disease, passed on when both parents are unaffected carriers.
NCERT Extract:
Mendelian Disorders – “… Haemophilia : This sex linked recessive disease, which shows its transmission from unaffected carrier female to some of the male progeny has been widely studied.”
Mendelian Disorders – “… Sickle-cell anaemia : This is an autosome linked recessive trait that can be transmitted from parents to the offspring when both the partners are carrier for the gene (or heterozygous).”
Mendelian Disorders – “… Phenylketonuria : This inborn error of metabolism is also inherited as the autosomal recessive trait.”
Mendelian Disorders – “… Thalassemia : This is also an autosome-linked recessive blood disease transmitted from parents to the offspring when both the partners are unaffected carrier for the gene (or heterozygous).”