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.
Failure of segregation of chromatids during cell division results in:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Aneuploidy
Chromosomal disorders are caused by the absence, the excess or the abnormal arrangement of one or more chromosomes. When the chromatids fail to separate during cell division, one cell gets an extra chromosome and the other loses one. This gain or loss of one or a few chromosomes is called aneuploidy. In Down’s syndrome there is an extra copy of chromosome 21. In Turner’s syndrome one X chromosome is lost.
(1) Apomixis — Incorrect. It is the formation of seeds without fertilisation. It is a kind of asexual reproduction in flowering plants.
(2) Aneuploidy — Correct. It is the gain or loss of one or a few chromosomes.
(3) Polyploidy — Incorrect. It results when the cytoplasm fails to divide (failure of cytokinesis) after telophase. This increases a whole set of chromosomes. It is often seen in plants.
(4) Parthenocarpy — Incorrect. It is the formation of fruit without fertilisation, so the fruit has no seeds. It has nothing to do with chromosome numbers.
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) 2024 on 15-05-2024 (Slot 1).
NCERT Extract:
Chromosomal Disorders –
