Margaret M. Loos
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I. Objectives:
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1. To update and consolidate student’s concept of a chromosome.
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2. To present visual material for physical and mentaL manipulation.
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3. To encourage curiosity about the structure and function of the chromosome as the unit of inheritance.
II. At this time in the study of genetics an appropriate definition of a chromosome might be “a linear aggregation of genes to form a chain of DNA and proteins”. The word chromosome comes from “chromo” meaning color and “some” meaning body. These colored bodies were named by Dr. W. Waldeyer in Germany in 1886 shortly after they were first seen by Schneider in 1883. Their ability to be stained by the dye, fuchsin, suggested by the name.
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Within the nucleus of the cells of each species there are a given number of chromosomes especially visible during cell replication. In humans, the
euploid
number or normal number, of chromosomes present in all cells is 23, 1 pair of sex chromosomes (xx designating female) and xy designating male) and 22 pair termed
autosomal
that carry the genetic material for all other general body functions. The two chromosomes of a given pair are called
homologous
an abnormal number of chromosomes be
aneuploid
, the 23 pair or 46 chromosomes is the
diploid
number and in the gametes or sex cells there is one of each pair or 23
haploid
number.
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Chromosomes are collected by bursting cells obtained from certain body tissues in hypotonic solutions after straining them with particular dyes for visibility they are assigned groupings and numbered. The groupings are determined by the size of the chromosome and the position of the
centromere
, the site of attachment of the microtubular spindle fibers present during the duplication of the chromosomes.
The setting up of chromosomes in this order is called karyotyping. Please use this chromosome group from a burst cell and make an arrangement of homologous chromosomes consisting of eight groups with 3, 2, 7, 3, 3, 2, 2 and the 1 sex chromosome pair in each. The sex chromosomes are circled. When you are finished let’s compare your arrangement with the laboratory prepared karyotype. Remember that the chromosomes are arranged according to longest to shortest and subdividions by the centromere position.
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Is this individual a male or female?
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This human karyotype was prepared by a modified staining technique. What can you now observe in the chromosomes?
