During crossing over, which occurs during prophase I of meiosis, homologous chromosomes exchange genetic material. Each chromosome in a homologous pair consists of two sister chromatids, and during this process, segments of DNA are swapped between the chromatids of the homologous chromosomes.
Here’s a more detailed breakdown of what happens:
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Pairing of Homologous Chromosomes: Homologous chromosomes are aligned closely together. Each chromosome has a corresponding partner that is similar in shape and size but may carry different alleles (versions of genes).
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Formation of Chiasmata: At specific points (called chiasmata), the chromatids of homologous chromosomes physically break and rejoin with their counterparts. This process creates the potential for genetic recombination.
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Exchange of Genetic Material: During this rejoining, segments of DNA are exchanged between the non-sister chromatids. As a result, the chromatids that were originally identical now contain a mix of alleles from both parents.
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Creation of Genetic Diversity: The result of crossing over is the formation of new allele combinations on each chromosome. This increases genetic diversity in the gametes (sperm and eggs), which is essential for evolution and adaptation in populations.
In summary, crossing over leads to genetic recombination, where homologous chromosomes exchange DNA, resulting in chromatids that have a unique combination of genes. This increases variation in the offspring.
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