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Genetic Recombination

Also Known as Cross-over

The animation in the header shows the process of genetic recombination in only two chromosome pairs (tetrads). In reality everything that is happening to these tetrads is happening simultaneously to the other 21 tetrads (or 20 in the case of males). The result is always four cells, each having a single #1 chromosome, and one #2 and one #3 and so on up to one each of 23 chromosomes. Thus each cell has one complete set of chromosomes and is ready to become either a sperm or egg cell.

Each person has 23 pairs of chromosomes in each cell. One member of each pair comes from our mother and one from our father. As part of egg and sperm cell production, the chromosome pairs are split up and distributed independently and randomly in a way that each sperm or egg receives one member of each pair.

When sperm and egg join during fertilization, the resulting gamete receives one member of each pair of chromosomes from its father and one from its mother. As the cells divide to form a new organism, each cell of that organism receives an exact copy of each of those 23 chromosomes.

The sorting process of meiosis insures that the chromosomes received by each sperm and egg cell are distributed independently and randomly.

Each sperm or egg is produced independently of the others. Each sperm or egg cell produced by an individual will share a significant amount of DNA with all the others produced by that person but none will be exactly the same.

It's all very simple. . . Except there is a one little complication. . .

Cross-over or Recombination

Before they separate and leave for their respective sperm or egg, the members of each pair team up and entwine (in one last farewell embrace). In the process, they exchange bits and pieces of themselves. "Take this bit to remember me by, my dear."

The result is that each of our chromosomes is a patchwork of DNA received from our father’s parents and our mother’s parents. This is called genetic recombination or more commonly cross-over. Cross over can occur at any location on a chromosome and it can occur at several locations at the same time. It is estimated that during each meiosis in humans, there is an average of two to three crossovers for each pair of homologous chromosomes.

When the chromosomes arrive in the new organism, they are a mosaic of DNA from all four grandparents. And since the grandparents received their DNA in the same way, the chromosomes are actually a mix of DNA from many ancestors who lived far back in time. Of course, as the DNA is passed through the generations, the contribution from more distant ancestors becomes increasingly fragmented and smaller. In many instances, we share no DNA from some of our more distant ancestors.

Where Can I Go From Here?

©️2002 - 2017 is a not for profit, educational website.

Where Can I Go From Here? is a not for profit, educational website.

©️2002 - 2017