Meiosis

Meiosis is a special type of cell division necessary for sexual reproduction. In animals, meiosis produces gametes like sperm and egg cells, while in other organisms like fungi it generates spores. Meiosis begins with one diploid cell containing two copies of each chromosome—one from the organism’s mother and one from its father—and produces four haploid cells containing one copy of each chromosome. Each of the resulting chromosomes in the gamete cells is a unique mixture of maternal and paternal DNA, ensuring that offspring are genetically distinct from either parent. This gives rise to genetic diversity in sexually reproducing populations, which enables them to adapt during the course of evolution.

Prophase 1

Before meiosis, the cell’s chromosomes are duplicated by a round of DNA replication. This leaves the maternal and paternal versions of each chromosome, called homologs, composed of two exact copies called sister chromatids and attached at the centromere region. In the beginning of meiosis, the maternal and paternal homologs pair to each other. Then in Prophase 1 they typically exchange parts by homologous recombination, leading to crossovers of DNA from the maternal version of the chromosome to the paternal version and vice versa. Spindle fibers bind to the centromeres of each pair of homologs and arrange the pairs at the spindle equator. Then the fibers pull the recombined homologs to opposite poles of the cell. As the chromosomes move away from the center, the cell divides into two daughter cells, each containing a haploid number of chromosomes composed of two chromatids. After the recombined maternal and paternal homologs have separated into the two daughter cells, a second round of cell division occurs. There meiosis ends as the two sister chromatids making up each homolog are separated and move into one of the four resulting gamete cells. Upon fertilization, for example when a sperm enters an egg cell, two gamete cells produced by meiosis fuse. The gamete from the mother and the gamete from the father each contribute half to the set of chromosomes that make up the new offsping’s genome.

Edited from Wikipedia and youtube by Deskarati

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2 Responses to Meiosis

  1. alfy says:

    One of the problems with trying to explain complex processes is not to bamboozle your hearers with too many technical terms all at once. Both clips suffer from this fault. A person may be able to keep one or two new terms in their head but when it runs to four or five you are going to lose them. As a teacher, ask yourself how many terms do you REALLY need in a introductory? If they are doing A levels and need to reproduce the ideas for an exam the full bank of technical terms is necessary. For the general reader it can be cut considerably. This aids explanation in simple terms.

    The Prof in the clip has not really thought through his presentation. As soon as he produces the poppit-bead chromosomes on screen he whisks them out of sight. A little later he says that he has got ahead of himself and should not have done that. Exactly. More careful planning of the presentation is needed. Frankly, brightly coloured clothing, breathless enthusiasm, and use of “cool” expressions is not going to make up for lack of clarity in his presentations.
    It is a pity that Sister Mary Wonderful at his junior school failed to teach the Prof to write properly, either all in lower case, or all in capitals rather than his rather childlike scattering of caps and lower case indiscriminately through a short word.
    The animation clip is also not much of an introductory. It quickly takes for granted that the viewer is familiar with a whole raft of technical terms, and can keep up with fast-moving animated processes. It may be a good revision clip for a bright student who has grasped the basis of the process, but it is too difficult for beginners. The bright sparkling colours and encouraging female voice can lead you to believe that you have understood everything much better than is really the case.

  2. Deskarati says:

    Well, although these presentations leave a lot to be desired, they both offer more than my Wednesday night teachers on the subject of parental DNA crossover!!!

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