Crossing over in meiosis does NOT influence:
a) Distance between genes
b) Presence of inversions
c) Enzyme activity
d) Cell cycle phase
The correct answer and explanation is:
The correct answer is: d) Cell cycle phase.
Explanation:
Crossing over is a key event during meiosis, the process by which gametes (sperm and egg cells) are formed. This process occurs during prophase I, where homologous chromosomes pair up and exchange genetic material. The primary function of crossing over is to increase genetic variation by creating new combinations of alleles on each chromosome.
Now, let’s analyze the options:
- Distance between genes (a):
Crossing over does influence the distance between genes. The likelihood of crossing over between two genes depends on their physical distance on the chromosome. Genes that are far apart have a higher chance of recombination (crossing over), while genes that are close together are less likely to undergo crossing over. This phenomenon is the basis for genetic mapping, where the frequency of recombination between genes is used to estimate their relative distances. - Presence of inversions (b):
Inversions refer to segments of chromosomes that have been flipped in orientation. Crossing over can be affected by inversions, as the inversion loop can prevent or alter the normal exchange of genetic material. Inversions typically reduce the likelihood of normal recombination in the affected region. - Enzyme activity (c):
Crossing over can indirectly influence enzyme activity. After meiosis, the recombination event might result in the production of proteins with altered functions due to the mixing of alleles. However, crossing over itself does not directly alter enzyme activity during meiosis. - Cell cycle phase (d):
Crossing over has no direct influence on the cell cycle phase. The cell cycle consists of interphase (G1, S, and G2 phases) and mitosis (M phase). Crossing over occurs in prophase I of meiosis, but it does not alter the progression or timing of the cell cycle phases. The mechanisms that regulate the cell cycle are independent of the genetic recombination process.
Therefore, crossing over does not influence the cell cycle phase.