Human Chromsomes

Studying Human Chromosomes





StarAsia Thomas
Mach.31.2012
Benjamin Banneker Academy
Living Environment Pd.2nd




StarAsia Thomas Benjamin Banneker Academy
March.31.2012 Living Enviornment Pd.2nd





Background

The name karyotype is given to the set of chromosomes of an individual, usually when visualized and identified under the microscope. The visualization generally is made with the cells in the initial phases of cell division for the chromosomes to be seen already replicated and condensed.The counting and identification of chromosomes in the karyotype of an individual can diagnose the aneuploidies, diseases caused by alteration in the number of chromosomes in relation to the normal number of the species.Down syndrome is an aneuploidy, i.e., a numeric alteration of chromosomes within the cells compared to the normal number of chromosomes of the species. Affected individuals have in their cells an additional chromosome 21 instead of only one pair. For this reason the condition is also called trisomy 21. The affected person has karyotype with 47 chromosomes: 45 + XY or 45 + XX..

Aneuploidy is an abnormal number of chromosomes in the cells of an individual.The main aneuploidies of the human species and their respective conditions are: the nullisomies (absence of any chromosome pair of the species, often incompatible with life); the monosomies (absence of a chromosome from a pair, for example, Turner’s syndrome, 44 + X); the trisomies (an extra chromosome, for example, the triple X syndrome, 44 + XXX, or the Edwards syndrome, trisomy 18, 45 + XY or 45 + XX).Generally the aneuploidies are caused by impaired assortment of chromosomes during meiosis. For example, when the homologous chromosomes of the pair 21 do not separate gametes with two chromosomes 21 and gametes without chromosomes 21 form. If a gamete with two chromosomes 21 fecundates a normal gamete of the opposite sex the zygote will present...