Question

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:

• A. Apomixis
• B. Aneuploidy
• C. Polyploidy
• D. Parthenocarpy

Hint:

Non-disjunction of a chromatid pair gives one chromosome extra or missing.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
During anaphase the sister chromatids separate and go to opposite poles. If they fail to separate, one daughter cell gets an extra chromosome and the other loses one. This is called non-disjunction.

Step 2: Name the result:
Gain or loss of one or a few chromosomes, so that the number is not an exact multiple of the haploid set, is called aneuploidy. Down syndrome (trisomy 21) is an example.

Step 3: Check the other options:
Apomixis is the formation of seeds without fertilisation. Polyploidy is a gain of whole sets of chromosomes, and it arises when the whole set fails to separate and not just a chromatid. Parthenocarpy is the formation of fruit without fertilisation. So options 1, 3 and 4 are wrong.

Final Answer:
Failure of chromatid segregation gives aneuploidy, which is option 2.