Crossing over is directly related to genetic variation as it is a key process that occurs during meiosis, where homologous chromosomes (one from each parent) exchange genetic material. This exchange happens between non-sister chromatids and creates new combinations of alleles, resulting in genetic diversity among offspring. Here’s how crossing over contributes to variation:

• During meiosis I, homologous chromosomes pair up and form structures called tetrads.
• At the points called chiasmata, segments of DNA are exchanged between chromatids.
• This recombination produces chromosomes with mixed genetic material from both parents.
• The new combinations of alleles increase the genetic variation within a population.
• This genetic diversity is crucial for natural selection and evolution, as it allows populations to adapt to changing environments.

In summary, crossing over shuffles alleles to create unique genetic combinations, providing the raw material for variation and evolution in sexually reproducing organisms.