Inheritance and disorders
Read the passage carefully and answer the given questions.
Mutation is a phenomenon which results in alteration of DNA sequences and consequently results in changes in the genotype and the phenotype of an organism. In haemophilia, a single protein that is a part of the cascade of proteins involved in the clotting of blood is affected. Due to this, in an affected individual a simple cut will result in non-stop bleeding. The heterozygous female for haemophilia may transmit the disease to sons. The possibility of a female becoming a haemophilic is extremely rare because mother of such a female has to be at least carrier and the father should be haemophilic. Sickle-cell anaemia is an autosome linked recessive trait that can be transmitted from parents to the offspring when both the partners are carrier for the gene. The disease is controlled by a single pair of allele, HbA and HbS. The chromosomal disorders on the other hand are caused due to absence or excess or abnormal arrangement of one or more chromosomes. Failure of segregation of chromatids during cell cycle results in the gain or loss of a chromosome, called aneuploidy.
Which one of the following disorders occurs due to loss of an X chromosome in human females?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Turner’s syndrome
The failure of chromatids to separate during cell division can lead to the gain or loss of a chromosome. This is called aneuploidy.
(1) Down’s syndrome — Incorrect. There is a gain of an extra copy of chromosome 21.
(2) Turner’s syndrome — Correct. One X chromosome is lost, so a female has 45 chromosomes (XO).
(3) Thalassemia — Incorrect. This is a Mendelian blood disorder in which the making of one of the globin chains of haemoglobin is reduced. It is not caused by loss of a chromosome.
(4) Klinefelter’s syndrome — Incorrect. This is a gain of an extra X chromosome in a male (XXY).
Note 1: 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.
Note 2: A similar question was also asked in CUET (UG) 2025 on 30-05-2025 (Slot 1).
NCERT Extract:
Chromosomal Disorders – …
