![]() ![]() If we add the effects of crossing over, the number of combinations increases even further. This means that there are over 8 million possible combinations just through the radom orientation of the homologous chromosmes. For example, for a haploid number of n, 2 n is the number of possible outcomes. The number of possible orientations is equal to 2 raised to the power of the number of chromosome pairs. Since the homologous pairs of chromosomes are orientated randomly at the equator, either maternal or paternal homolgue can orient towards either pole. The random orientation of homologous chromosomes at the equator in metaphase I also plays a vital role in genetic variety. This means that meiosis can result in almost an infinite amount of genetic variety. It is also important to note that crossing over occures at a random point and more than one chiasma can form per homologous pair. The chromatids which have a combination of allele different to that of either parent are called recombinants. This forms chromatids with new combinations of alleles (recombination of linked genes). These are crossing over in prophase I and the random orientation of chromosomes in metaphase I.Ĭrossing over is important for genetic variety as it allows the exchange of genetic material between the maternal and paternal chromosomes. Two processes result in the infinite genetic variety in gametes. In gametes through crossing over in prophase I and random orientation in metaphase I. 10.1.3 Explain how meiosis results in an effectively infinite genetic variety The chiasma links homologous chromosome pairs together and remains until late metaphase I. Once crossing over is finnished the homologous chromosomes are no longer tightly linked however the connection between the non-sister chromatids remains, forming an X - shaped structure called a chiasma. Paternal and maternal chromosomes can then exchange genetic material. The DNA of the one chromatid binds to the DNA of the non-sister chromatid. Following this another cut is made at the same point in the DNA molecule of a non-sister chromatid. A cut is made in the DNA molecule of one of the chromatids. In prophase I the four sister chromatids of a pair of homologous chromosomes become tightly linked in a process called synapsis. Both cells undergo cytokinesis to form four cellsįigure 10.1.2 - Meiosis II 10.1.2 Outline the formation of chiasmata in the process of crossing over.Nuclear membrane forms around the chromatids at each pole , once the membrane is formed, each chromatid is then called a chromosome.Chromatids of each chromosome travel to opposite poles.Spindle fibers attach to the the centromeres.At the end of telophase I the cells may enter a short interphase period or proceed directly to meiosis II.The cell undergoes cytokinesis to form two daughter cells.A nuclear membrane forms around the chromosomes at each pole and chromosomes uncoil. ![]() Paired homologous chromosomes are seperated and pulled to opposite poles so that each pole contains one chromosome of each pair.Spindle fibers shorten pulling paired homologous chromosomes in opposite directions.Pairs of homologous chromosomes align along the equator.Microtubules form a spindle and the spindle fibers attach to the centromeres of the chromosomes.Nuclear membrane disintgrates and the centrioles travel to the poles of the cell. ![]()
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