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B chromosomes are a particular kind of supernumerary chromosomes which have been used for chromosome mapping. Which of the following is not a characteristic feature of B chromosomes?

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  1. They are dispensable and are not found in all individuals of a species.
  2. They are not homologous with any of the basic A chromosomes.
  3. Their inheritance is mendelian
  4. When present in high number, they suppress vigour and fertility.

Answer (Detailed Solution Below)

Option 3 : Their inheritance is mendelian
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Detailed Solution

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The correct answer is Their inheritance is Mendelian

Concept:

  • B chromosomes are a type of supernumerary chromosome, meaning they are additional chromosomes beyond the standard set (A chromosomes) found in a species.
  • Unlike A chromosomes, which are essential for normal growth, development, and reproduction, B chromosomes are often dispensable and may not be present in all individuals of a species.
  • B chromosomes have been used for chromosome mapping due to their unique properties and behaviors.

Explanation:

  • Option 1: They are dispensable and are not found in all individuals of a species. This is a characteristic feature of B chromosomes. They are not necessary for survival and may vary in number among individuals within the same species.
  • Option 2: They are not homologous with any of the basic A chromosomes. This is also true. B chromosomes do not have homologous pairs among the standard set of chromosomes (A chromosomes) and often contain different genetic material.
  • Option 4: When present in high number, they suppress vigor and fertility. This is a known characteristic of B chromosomes. High numbers of B chromosomes can have detrimental effects on the organism, including reduced vigor and fertility.

Additional Information

  • B chromosomes are often composed of repetitive DNA sequences and may carry genes, but these genes are usually not essential for survival.
  • The presence and number of B chromosomes can vary widely even within a single species, making them a subject of interest in genetic studies and chromosome mapping.
  • Research on B chromosomes has provided insights into chromosome behavior, evolution, and the mechanisms of non-Mendelian inheritance.
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