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Meiosis Introduction
Reproduction
Flowering plants, known as angiosperms, reproduce sexually to create seeds that become the new generation. In general, a cell with a complete set of chromosomes is called a diploid cell. All cells that carry only half of the genetic material are called haploid cells. The total number of chromosomes varies between different types of organisms, so scientists use the letter n as a variable to represent the number for each individual. That means that diploid cells are 2n, to represent a complete set of chromosomes, and haploid cells are n, or half the diploid number. Sexual reproduction requires two sex cells or gametes with a haploid number (n) of chromosomes to unite and form a diploid cell (2n). The process of creating haploid cells is called meiosis.
MeiosisThe creation of haploid cells requires two cycles of division known as Meiosis I and Meiosis II. Somatic cells, cells of the body, do not go through meiosis, but rather they only go through mitosis. Specialized sex cells go through meiosis to create 4 new cells with half the DNA of the parent cell. Before meiosis can begin, the DNA in a diploid cell must replication and condenses to form homologous chromosomes. In the picture of homologous chromosomes, the bands on the chromatids depict locations of genes. The letters infer the gene influence on a specific trait.
During prophase 1 of meiosis, the chromosomes will attach to one another and form what is known as a tetrad in which a process called crossing over occurs. During crossing over, the non-sister chromatids exchange a leg segment that contains a different gene sequence. The new gene sequence from the exchange influences the same traits as the original sequence, but the influence may be different.
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