Lab 4 Protocol - Genetics 310 Human Chromosome Studies...

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Genetics 310 Human Chromosome Studies Introduction Chromosomes are highly specialized cellular structures that contain most of the genetic information, as DNA, within eukaryotic cells (with mitochondria and chloroplasts also carrying much smaller amounts of genetic information). Because of the unique properties chromosomes have, nuclear DNA can be can replicated, repaired, and transcribed with great efficiency. Most higher organisms are diploid (2n), possessing two copies of each type of chromosome (with the sex chromosomes being an exception). The accuracy of the process of mitosis, the creation of two identical daughter cells, each with 2n chromosomes, is critical to the health of individual cells and of the organism. Human beings have 46 chromosomes, with 22 pair being called autosomes, with two sex chromosomes, XX for females and XY for males. Modern technology allows us to be able to visualize the form chromosomes take in metaphase of mitosis, their most highly condensed stage. The drug colchicine, applied to dividing cells in culture, acts to disrupt the microtubules that make up the mitotic spindle. This treatment inhibits the onset of metaphase and anaphase, the stages when the chromatids would normally line up before being pulled to opposite poles of the cell due to their attached microtubules. Cells prepared in this way can then be spread on microscope slides using a technique that results in the nuclear chromosome set being separated enough to identify each type of chromosome by its size, centromere placement, and unique banding pattern. Images of these are sorted into pairs and studied to determine whether they show a normal or an abnormal total numbers or banding pattern. This chromosomal image is called a karyotype . Various human abnormalities have been found to correlate with abnormal karyotypes. This is understandable when one realizes that even a short portion of a single chromosome that is duplicated or deleted could affect the level of expression of hundreds of genes. In today’s lab, you will have the chance to study human karyotypes, and disease states related to abnormalities, in a few different ways: A. preparation and study of a slide showing human chromosomes from HeLa cells , a well- known cell line established in the 1950s from human cervical cancer tissue. B. observation and imaging of commercial, prepared slides of normal or abnormal human chromosomes. C. identification and sorting of both actual and stylized human metaphase chromosomes on paper, and using an online computer activity to determine whether they are normal or abnormal in type and/or number.
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