What is the primary outcome of a nondisjunction event occurring during meiosis?
Solution
Correct Answer: Option A
The primary outcome of a nondisjunction event occurring during meiosis is the production of gametes with abnormal chromosome numbers.
During meiosis, homologous chromosomes (in Meiosis I) or sister chromatids (in Meiosis II) are supposed to separate evenly into daughter cells. However, when nondisjunction occurs, this separation fails, leading to one daughter cell receiving both copies of a chromosome and the other receiving none. As a result, the gametes produced have an aneuploid chromosome number — either an extra chromosome (trisomy) or missing a chromosome (monosomy).
This abnormal chromosome number can cause developmental disorders if such gametes participate in fertilization. Examples include Down syndrome (trisomy 21) and Turner syndrome (monosomy X).
To clarify the other options:
- Increased crossover frequency (Option 2) relates to genetic recombination, not nondisjunction.
- Enhanced genetic variability (Option 3) results from normal recombination and independent assortment, not from errors like nondisjunction.
- Failure of spindle fiber attachment (Option 4) can lead to nondisjunction but is not the primary outcome; it is rather a possible cause.
In summary:
Nondisjunction leads directly to gametes with abnormal chromosome numbers, which is the primary consequence observed in this meiotic error.
Reference: Essential Medical Genetics, Volume 2, Chapter 6, p. 145-147
During meiosis, homologous chromosomes (in Meiosis I) or sister chromatids (in Meiosis II) are supposed to separate evenly into daughter cells. However, when nondisjunction occurs, this separation fails, leading to one daughter cell receiving both copies of a chromosome and the other receiving none. As a result, the gametes produced have an aneuploid chromosome number — either an extra chromosome (trisomy) or missing a chromosome (monosomy).
This abnormal chromosome number can cause developmental disorders if such gametes participate in fertilization. Examples include Down syndrome (trisomy 21) and Turner syndrome (monosomy X).
To clarify the other options:
- Increased crossover frequency (Option 2) relates to genetic recombination, not nondisjunction.
- Enhanced genetic variability (Option 3) results from normal recombination and independent assortment, not from errors like nondisjunction.
- Failure of spindle fiber attachment (Option 4) can lead to nondisjunction but is not the primary outcome; it is rather a possible cause.
In summary:
Nondisjunction leads directly to gametes with abnormal chromosome numbers, which is the primary consequence observed in this meiotic error.
Reference: Essential Medical Genetics, Volume 2, Chapter 6, p. 145-147
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