Crossing Over
- Having genetically different offspring can be advantageous for natural selection
- Meiosis has several mechanisms that increase the genetic diversity of gametes produced
- Both crossing over and independent assortment (random orientation) result in different combinations of alleles in gametes
- Crossing over is the process by which nonsister chromatids exchange alleles
- Process:
- During meiosis I homologous chromosomes pair up and are in very close proximity to each other
- The nonsister chromatids can cross over and get entangled
- These crossing points are called chiasmata
- The entanglement places stress on the DNA molecules
- As a result of this a section of chromatid from one chromosome may break and rejoin with the chromatid from the other chromosome
- This trading of alleles is significant as it can result in a new combination of alleles on the two chromosomes
- There is usually at least one, if not more, chiasmata present in each pair of homologous chromosomes during meiosis
- Crossing over is more likely to occur further down the chromosome away from the centromere
Crossing Over Diagram
Crossing over increases genetic diversity by recombining alleles