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Meiosis and Development: Cutting the Ties That Bind (Article Critique Sample)


Meiosis and development: cutting the ties that bind

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Title: Chapter 3 Meiosis and Development
Subtitle: Meiosis: Cutting the Ties That Bind
Meiosis is a special type of reproductive cell division which occurs only in the generation of thegametes or germ cells that are responsible for fertilisation and hence formation of new offspring. Meiotic celldivision reduces (halves) thechromosomal content and hence the production of four haploid cells. The overallprocess of germ cell development is called "gametogenesis” which is oogenesis and spermatogenesis andincludes not only meiosis but alsothe cellular changes that occurdifferently in male and female germ cells.
The development of a new organismfrom the joining of two single cells isa complex and carefully orchestrated process. But even before sperm meets egg, anequally elaborate set ofchoreographed steps must occur toensure successful fertilization and therefore resulting in successful sexualreproduction that will lead to formation of the offspring. Those steps, known asreproductive cell division or meiosis, split the original number of chromosomes in half so that offspring will inherit half their genetic material from one parent and half from theother. During this process, each set of homologous chromosomes pair up in a kind of chromosomal square dance a process called synapses that will lead crossing over and hence variation in secies. Chromosome 1with chromosome 1, chromosome 2 with chromosome 2, and so on down the line. The two gamete cells stick together, dancing through the phases of meiosis both meiosis I and meiosis II until it is time to segregate or separate to opposite ends of the dividing cell. When the chromosomes don’t pair or part appropriately it can result in eggs and sperm with the wrong number of chromosomes, a major cause of miscarriage and birth defects. In order to avoid these mistakes, most chromosomes use a process that allows exchange of genetic information to take place, a process known as crossing over. In this case chromosomes loop their arms with their partners and even swapping pieces of genetic material to stick together until the dance (crossing over) is over. A few chromosomes, like chromosome 4 in the fruit fly Drosophila melanogaster, are too short to make these crossovers and hence the process of crossing over is not suitable for all species of living organisms. This species have somehow, figured out another way to stay connected to their partners.
Stacie E. Hughes, Ph.D., a research specialist II at the StowersInstitute for Medical Research, identified the threads of DNA that seemed to tie these other homologous chromosomes together in pairs. The major objection that still remained was: once these chromosomes are roped into pairs, how...
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