INTRODUCTION
The complete set of chromosomes in the body cell of a species is known as karyotype. Karyotype is a test to identify and evaluate the size, shape, and number of chromosomes in a sample of body cells. Any abnormalities such as extra, missing, or abnormal positions of chromosome pieces can cause problems with a person growth, development and body functions.
Karyotype can be used to determine whether the chromosomes of an adult have an abnormality that can be passed on to the child. It can also determine whether a chromosome defect is preventing a woman from becoming pregnant or causing miscarriages. There are so many problems that involves chromosomes can be determined by using the karyotype. Next, to create a karyotype, chromosomes from a cell are stained and photographed.
The photograph is enlarged and cut up into individual chromosomes. In this experiment, the homologous pairs are identified and arranged in order by size and ended with sex chromosomes. This test is typically done on a sample of blood, although any body cell could be used. The cell must undergo mitosis, which it is preferable in metaphase, so that the chromosomes are replicated, condensed, and visible under a microscope.
OBJECTIVES
- To understand what a karyotype is and how it is performed.
- To understand the reason for performing a karyotype, especially for those with a higher risk of genetic defect in their lineage.
- To determine what genetic defect is present in a chromosomes sample.
- To investigate a variety of genetic disorders that commonly occur and are studied in biology classes.
MATERIALS
- Scissors
- Glue
- Ruler
- Small envelope
METHODS
- The attached sheet was used to complete one out of two normal karyotypes ( Chromosome Pic #2 and #3) and another out of the four sets of abnormal karyotypes ( Set A, B, C, and D).
- The chromosome on the pages that have been chosen was cut by using a scissors and the EXACT match was searched elsewhere on the page. This chromosome was cut out and BOTH chromosomes were glued side by side on a data table.
- This procedure continued until each of the chromosomes were matched and glued in the data table. DO NOT CUT OUT ALL CHROMOSOMES AND THEN ATTEMPT TO MATCH THEM. Cut out only one at a time or you will lose your chromosome.
- DO NOT THROW OUT ANY EXTRA CHROMOSOME as it is the chromosomes that cause mutation/disorder and it have to be matched correctly.
- After all of the chromosomes were cut out and included in the karyotype, the questions were answered.
DISCUSSION
Based on this experiment, by referring to chromosome Picture #3 we can see that it is a normal human karyotype where it contains 22 pairs of autosomal chromosomes and 1 pair of sex chromosomes. That will total up to 46 chromosomes and 23 pairs. Sex is determined by X and Y chromosomes, as it contains two X chromosomes, it is a normal karyotype for females and is denoted as 46, XX. The sex is determined by the sex chromosome carried in the sperm.
We can also see that the size and shape are arranged in a standard manner. The chromosome is described initially on morphology and also banding patterns. Morphologically, it is classified by referring to the location of the centromere where it can be Metacentric, Submetacentric, and Acrocentric for human chromosome. Metacentric chromosomes have the centromere placed at or near the middle of the chromosome. Both arms of the chromosomes are about equal length, for example, chromosome 1 and chromosome
Next, Submetacentric chromosomes have their centromere located closer to one end of the chromosomes than the other, which means one chromosome arms is longer than the other but there are still clearly two chromosomes arms, for example, chromosome 5 and chromosome 8. Lastly, Acrocentric chromosomes that have their centromere close to one end. There is a secondary constriction thin strand of chromatin of variable length tipped with non-coding DNA often referred to as chromosomal satellites, for example, chromosomes 13, 14 and 15.
Besides that, chromosomes arms are designated as “p” for short arm and ‘q” for the long arm. Next, based on the abnormal karyotypes (Set B), we can see that there is an extra of X chromosomes of the sex chromosomes. This abnormality is identified as Klinefelter syndrome. It is one of male chromosomes abnormalities, where males inherit one or more extra X chromosomes and their genotype is XXY or more rarely XXXY or XY/XXY mosaic.
This person will have relatively high-pitched voices, asexual to feminine body contours as well as breast enlargement, and comparatively little facial and body hair. They are sterile and their testes and prostate gland are small. As a result, they produce relatively small amounts of testosterone. However, the feminizing effects of this hormonal imbalance can be significantly diminished if Klinefelter syndrome boys are regularly given testosterone from the age of puberty on. Many Klinefelter syndrome men are an inch or so above average height. They also are likely to be overweight. They usually have learning difficulties as children, especially with language and short-term memory. If not given extra help in early childhood, this often leads to poor school grades and a subsequent low self-esteem.
However, most men who have Klinefelter syndrome are sufficiently ordinary in appearance and mental ability to live in society without notice. It is not unusual for Klinefelter syndrome adults with slight symptoms to be unaware that they have it until they are tested for infertility. They are usually capable of normal sexual function, including erection and ejaculation, but many, if not most, are unable to produce sufficient amounts of sperm for conception.
Klinefelter syndrome males with more than two X chromosomes usually have extreme symptoms and are often slightly retarded mentally. Men who are mosaic (XY/XXY) generally have the least problems. There is no evidence that Klinefelter syndrome boys and men are more inclined to be homosexual, but they are more likely to be less interested in sex. They have a higher than average risk of developing osteoporosis, diabetes, and other autoimmune disorders that are more common in women. This may be connected to low testosterone production. Subsequently, regular testosterone therapy is often prescribed.
The frequency of Klinefelter syndrome has been reported to be between 1 in 500 and 1 in 1000 male births. This makes it one of the most common chromosomal abnormalities. Males with Down syndrome sometimes also have Klinefelter syndrome. Both syndromes are more likely to occur in babies of older mothers.
CONCLUSION
In a conclusion, we can understand what a karyotype is and how it is performed. We can also understand the reason for performing a karyotype and determine what genetic defect is present in a chromosomes sample by referring to the normal and abnormal karyotypes. Besides, one of the genetic disorders that commonly occur can also be identified from the experiment, which is the Klinefelter syndrome.
QUESTIONS
How could you determine if your karyotype was male or female? We can determine whether the karyotype is female or male by referring to its sex chromosomes, either it is XX or XY. Female karyotypes denoted a 46, XX whereas male karyotypes denoted a 46, XY.
REFERENCES
- Karyotype. Retrieved on 2013 October, 20 from http://homepages.uel.ac.uk/V.K.Sieber/human.htm
- Wikipedia: Karyotype. Retrieved on 2013 October, 20 fromhttp://en.wikipedia.org/wiki/Karyotype#Depiction_of_karyotypes
