In the context of hereditary diseases, consider the following statements: 1. Chromosome abnormalities means an individual is either missing one of the chromosomes from a pair or has more than two chromosomes instead of a pair. 2. An individual with Down syndrome has three copies of chromosome 21 rather than two. Which of the following statements given above is/are correct?

Option 3 : Both 1 and 2

The correct answer is ​Both 1 and 2.

• Chromosome abnormalities are one of the genetic hereditary diseases.
• Most chromosome abnormalities occur as an accident in the egg or sperm. In these cases, the abnormality is present in every cell of the body.
• Some abnormalities, however, happen after conception; then some cells have the abnormality and some do not.
• Chromosome abnormalities can be numerical or structural.
• A numerical abnormality means an individual is either missing one of the chromosomes from a pair or has more than two chromosomes instead of a pair. Hence, statement 1 is correct.
  • When an individual is missing one of the chromosomes from a pair, the condition is called monosomy.
    • An example of monosomy, in which an individual lacks a chromosome, is Turner syndrome. In Turner syndrome, a female is born with only one sex chromosome, an X, and is usually shorter than average and unable to have children, among other difficulties.
  • When an individual has more than two chromosomes instead of a pair, the condition is called trisomy.
    • An example of a condition caused by numerical abnormalities is Down syndrome, which is marked by mental retardation, learning difficulties, a characteristic facial appearance and poor muscle tone (hypotonia) in infancy.
      • An individual with Down syndrome has three copies of chromosome 21 rather than two; for that reason, the condition is also known as Trisomy 21. Hence, statement 2 is correct.
• A structural abnormality means the chromosome's structure has been altered in one of several ways.
  • Deletions: A portion of the chromosome is missing or deleted.
  • Duplications: A portion of the chromosome is duplicated, resulting in extra genetic material.
  • Translocations: A portion of one chromosome is transferred to another chromosome. There are two main types of translocation. 
    • In a reciprocal translocation, segments from two different chromosomes have been exchanged.
    • In a Robertsonian translocation, an entire chromosome has attached to another at the centromere.
  • Inversions: A portion of the chromosome has broken off, turned upside down, and reattached. As a result, the genetic material is inverted.
  • Rings: A portion of a chromosome has broken off and formed a circle or ring. This can happen with or without the loss of genetic material.