Identify the Mendelian disorders from the following:
A. Down’s syndrome
B. Haemophilia
C. Cystic Fibrosis
D. Klinefelter’s syndrome
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → B and C only
Genetic disorders are of two kinds. Mendelian disorders are caused by an alteration (mutation) in a single gene and are inherited by Mendel’s principles. Chromosomal disorders are caused by the absence, excess or abnormal arrangement of whole chromosomes.
A. Down’s syndrome — Chromosomal disorder. It is caused by an extra copy of chromosome 21 (trisomy 21).
B. Haemophilia — Mendelian disorder. It is caused by a single defective gene on the X chromosome and is passed on as an X-linked recessive trait.
C. Cystic Fibrosis — Mendelian disorder. It is caused by a mutation in a single gene, and the book lists it among the common Mendelian disorders.
D. Klinefelter’s syndrome — Chromosomal disorder. It is caused by an extra X chromosome, giving the karyotype 47, XXY.
NCERT Extract:
Mendelian Disorders – “Broadly, genetic disorders may be grouped into two categories – Mendelian disorders and Chromosomal disorders. Mendelian disorders are mainly determined by alteration or mutation in the single gene. … Most common and prevalent Mendelian disorders are Haemophilia, Cystic fibrosis, Sickle-cell anaemia, Colour blindness, Phenylketonuria, Thalassemia, etc.”
Chromosomal Disorders – “The chromosomal disorders on the other hand are caused due to absence or excess or abnormal arrangement of one or more chromosomes. … Down’s syndrome, Turner’s syndrome, Klinefelter’s syndrome are common examples of chromosomal disorders.”