But this happens independently for each trait, so just because you got your dad's brown eyes doesn't mean you'll get his blond hair too. Each sperm and egg will end up with either B or b from mom and either B or b from dad. This leads to four possibilities: You could get B from mom and B from dad, or B from mom and b from dad, or b from mom and B from dad, or b from mom and b from dad. Imagine, for example, that eye color was controlled by a single gene, and that mom could have B, the allele for brown eyes or b, the allele for blue eyes, and dad could also have B or b. But each non-identical-twin child of these parents ends up with a different combination. You ended up with half of mom's paired genes and half of dad's paired genes. This DNA transfer is accomplished via crossing over and results in the creation of a recombinant bacterial cell.Your parents each have at least one pair of alleles (versions of a gene) for every trait (and many pairs of alleles for each polygenic trait). Once the foreign DNA is internalized by a bacterium via conjugation, transformation, or transduction, the bacterium can insert segments of the DNA into its own DNA. In transduction, bacterial DNA is exchanged through a virus that infects bacteria known as a bacteriophage. The DNA remnants in the environment most commonly originate from dead bacterial cells. In transformation, bacteria take up DNA from their environment. Genes are transferred from one bacterium to the other through this tube. In conjugation, one bacterium connects itself to another through a protein tube structure called a pilus. Bacterial recombination is accomplished by the processes of conjugation, transformation, or transduction. In bacterial recombination, genes from one bacterium are incorporated into the genome of another bacterium through crossing over. Although bacteria most commonly reproduce by binary fission, this mode of reproduction does not produce genetic variation. Prokaryotic cells, like bacteria which are unicellular with no nucleus, also undergo genetic recombination. These chromosomes, known as homologous chromosomes, are similar in length, gene position, and centromere location. During cell division, chromosomes form paired sets consisting of one chromosome from each parent. Each duplicated chromosome is comprised of two identical chromosomes called sister chromatids that are connected to the centromere region. When a cell enters the cell cycle, its chromosomes duplicate via DNA replication in preparation for cell division. A chromosome is typically single-stranded and consists of a centromere region that connects a long arm region (q arm) with a short arm region (p arm). So, now, it appears as if one long strand of red rope has a one-inch segment of blue on its end, and likewise, the blue rope has a one-inch segment of red on its end.Ĭhromosomes are located within the nucleus of our cells and are formed from chromatin (mass of genetic material consisting of DNA that is tightly coiled around proteins called histones). It switches places with a one-inch segment parallel to it on the blue rope. Now, cross one piece over the other to form an "X." While the ropes are crossed, something interesting happens: a one-inch segment from one end of the red rope breaks off. Each piece of rope represents a chromosome. Genetic recombination is responsible for genetic diversity in a species or population.įor an example of crossing over, you can think of two pieces of foot-long rope lying on a table, lined up next to each other. Genetic recombination happens as a result of the separation of genes that occurs during gamete formation in meiosis, the random uniting of these genes at fertilization, and the transfer of genes that takes place between chromosome pairs in a process known as crossing over.Ĭrossing over allows alleles on DNA molecules to change positions from one homologous chromosome segment to another. Genetic recombination produces genetic variation in organisms that reproduce sexually. Genetic recombination refers to the process of recombining genes to produce new gene combinations that differ from those of either parent.
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