Question

How do inversions suppress crossing over, leading to a chemical imbalance due to breakpoints within certain genes?

A) By promoting an increase in crossing over.
B) By facilitating a decrease in the number of breakpoints.
C) By creating a physical barrier to the recombination process.
D) By inducing mutations within genes flanking the inversion.

Answer 1

Inversions suppress crossing over by forming an inversion loop that acts as a physical barrier during meiosis, potentially causing genetic imbalance and aneuploid gametes if crossing over occurs within the inverted segment.

Step-by-step explanation:

Chromosome inversions suppress crossing over by creating a physical barrier to the recombination process. During meiosis, if one chromosome has an inversion and the other does not, the homologous chromosomes with an inversion must form an inverted loop to facilitate gene alignment and proper pairing. This atypical structure can prevent normal recombination, as crossover events could lead to an imbalance if they occur within the inverted segment, potentially resulting in genetic imbalance due to breakpoints within certain genes.

Moreover, inversions can disrupt regulatory relationships between genes and their expression controllers, which can cause aberrant gene product levels, having downstream effects on cellular function. The pairing difficulty caused by an inversion loop implies that recombination between inverted and non-inverted chromosomes is less likely, hence reducing the chance of crossing over within that region. This can lead to aneuploid gametes if crossing over does occur, causing a chemical imbalance.