Karyotype- Profile of a Person's Chromosomes
A karyotype is a profile of the sets of chromosomes found in the genes of a human being. It shows all the different sets of chromosomes that a person contains.
A normal individual will have 22 sets of autosomes, which are non-sex chromosomes. This means there will be 22 pairs of autosomes. This means 44 chromosomes will compose autosomes. The other 2 chromosomes are the sex chromosomes. These 2 chromosomes decides an individual's sex. If the chromosomes are XY, the individual is a male. If the sex chromosomes are XX, the individual is a female.
Below is the karyotype of a perfectly normal individual, composed of pairs (2 chromosomes each)
of 22 autosomes and 1 pair (2 chromosomes each) of sex chromosomes:
You can see that each autosome pair only has 2 chromosomes. There are no extra chromosomes or no missing
chromosomes. The individual above has two X chromosomes as the sex cells, which means the individual is a female.
Genetic Disorders
We will now discuss cases in which an individual has an abnormal karyotype, which is an abnormal
chromosome type. This means there are either chromosomes missing in the pairs or there are extra chromosomes. Both of
these conditions leads to an individual with a genetic disorder, which leads to developmental problems in that
individual.
Down's Syndrome- Trisomy 21
One genetic disorder that results from an abnormal count in the number of chromosomes in an individual is down's syndrome. Down's syndrome is an illness which can lead to varying degrees of mental retardation, the facial characteristic of a mon face, larger than normal, sometimes furrowed tongue, larger than normal hands with stubby fingers, and pseudoepicanthic fold. Down's syndrome is the most common type of chromosomal disorder in human beings.
Down's syndrome is called trisomy 21, because the 21st set of autosomes contains 3(tri) chromosomes. Remember, a normal individual has 2 chromosomes for each set. An individual with down's syndrome has 3 chromosomes in the 21st set. This is what leads to developmental problems.
Below is the karyotype of an individual with down's syndrome (again, trisomy 21):
You can see the 3 chromosomes present in the 21st set.
Edward's Syndrome- Trisomy 18
Another type of chromosomal abnormality is Edward's syndrome. This is a genetic disorder which causes severe heart and kidney defects, convec plantar surface of the foot (not a flat foot), and abnormal, low set auriculae.
It is called trisomy 18, because in the 18th set of autosomes, there are 3 chromosomes present (instead of the normal count of 2). This extra chromosome in the 18th set causes the all the developmental issues described above.
Below is the karyotype of an individual with Edward's Syndrome:
You can see the 3 chromosomes present in the 18th set. This causes Edward's syndrome.
Patau's Syndrome- Trisomy 13
Another type of chromosomal disorder is Patau's syndrome. This causes microcephaly, micropthalmia, usually blindness, heart defects, cleft lip and palate.
It is called trisomy 13, because in the 13th set of chromosomes, there are 3 chromosomes present (instead of the usual pair of 2). This, again, can be easily seen from the karyotype of an individual with this condition.
Below is the karotype of an individual with patau's syndrome (trisomy 13):
You can see the 3 chromosomes present in the 13th set.
Klinefelter's Syndrome- XXY
Klinefelter's syndrome is a genetic disorder in which an individual has 3 sex chromosomes instead of the usual 2; the person will possess the sex chromosomes XXY. This will make the individual a male, but he will also display some female characteristics. All of the sex organs are male, but only about a half of the size. Testes will show an absence of spermatozoa, with a possible presence of gynecomastia. Males who have klinefelter's syndrome may also develop small breasts.
Again, looking at the karyotype we can easily tell that a person has klinefelter's syndrome by the 3 chromosomes present in the sex chromosomes (XXY).
Below is the karyotype of an individual with Klinefelter's syndrome (XXY):
You can see 3 chromosomes present in the sex chromosomes of the individual, 2 X chromsomes and 1 Y chromosomes, for
an XXY set.
Turner's Syndrome- Monosomy with X0
Turner's Syndrome is a genetic disorder in which an individual only has one sex chromosome, an X chromosome. The symptoms of turner's syndrom is sexual infantilism, short stature, and webbing of the neck.
Turner's syndrome is also monosomy because there is only one chromosome present in the sex chromosomes instead of the usual 2. The chromosome, again, is an X chromosome. So the individual contains a X0 sex chromosome pair.
Below is the karyotype of an individual with Turner's Syndrome (monosomy X0):
You can see there is just one X chromosome without a complementary X or Y chromosome.
Supermale- XYY
A supermale is an individual who has 3 sex chromosomes, 1 X chromosome and 2 Y chromosomes, for a set of XYY.
The ramifications of being born a supermale is possible learning disabilities.
Below is the karyotype of a supermale individual (having XYY sex chromosomes):
You can see the 3 chromosomes, XYY, present in the sex chromosomes.
Superfemale- XXX
A superfemale is an individual who has 3 sex chromosomes, 3 X chromosomes, for a set of XXX.
The ramifications of being born a superfemale is deficiencies in speech development and verbal IQ.
Below is the karyotype of a superfemale individual (having XXX sex chromosomes):
In conclusion, these are different karyotypes showing normal individuals to a plethora and wide variety
of different genetic disorders that can result at births. As you can see, karyotypes can show if an individual has a
normal, healthy set of chromosomes or if he or she has any of the wide variety of chromosomal disorders, such as
syndromes. Thus, karyotypes serve as a type of X-ray or profile of an individual's chromosomes.
Related Resources
Down's Syndrome
Edward's Syndrome
Patau's Syndrome
Turner's Syndrome
Klinefelter's Syndrome
Supermale- XYY Syndrome
Superfemale- XXX Syndrome