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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?

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? Correct Answer Both 1 and 2

The correct answer is ​Both 1 and 2.

Key Points

  • 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.

Related Questions

Consider the following two tables and four queries in SQL. Book (isbn, bname), Stock (isbn, copies) Query 1: SELECT B.isbn, S.copies FROM Book B INNER JOIN Stock S ON B.isbn = S.isbn;   Query 2: SELECT B.isbn, S.copies FROM Book B LEFT OUTER JOIN Stock S ON B.isbn = S.isbn; Query 3: SELECT B.isbn, S.copies FROM Book B RIGHT OUTER JOIN Stock S ON B.isbn = S.isbn;   Query 4: SELECT B.isbn, S.copies FROM Book B FULL OUTER JOIN Stock S ON B.isbn = S.isbn;   Which one of the queries above is certain to have an output that is a superset of the outputs of the other three queries?
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3. Copies made from or compared with the original
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5. Oral accounts of the contents of a document by a person who has seen it
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