“The karyotype analysis reveals that males have one X and one Y chromosome and females have two X chromosomes with 22 pairs of autosomes.”
Male and female are two different living entities on earth and their difference makes it possible to reproduce. In almost every organism males and females are different. If we think in terms of physical appearance, the males are masculine and hairy due to high testosterone. On the other side, females are more feminine.
Interestingly if you are not aware of it, let me tell you both are also different genetically too. Before understanding their genetics first lets go through some basics.
All DNA is located on chromosomes (in a broad sense!) which is a complex network of DNA and proteins. The reason why chromosomes are there, is to fit all DNA inside the cell.
We, humans, have 23 pairs of chromosomes. If any abnormality occurs in chromosomes it ultimately causes genetic abnormalities. Serious developmental, mental, and intellectual problems occur due to this.
Common chromosomal abnormalities are translocations, duplications, deletions, insertions, and inversions. Besides, a change in the number of chromosomes is also one of them.
Some of the chromosomal abnormalities are enlisted in the table below,
|Trisomy 21||Three 21 chromosomes|
|Trisomy 18||Three 18 chromosomes|
|Monosomy X||A single X chromosome|
|Philadelphia chromosome||Translocation between 9 and 22|
|Disomy of X||XXY or klinefelter syndrome|
In every cell, we have 23 pairs of chromosomes (total 46) in which the 22 pairs are autosomes. And a pair of sex chromosomes. The X and Y are known as the sex chromosomes which take part in deciding the gender of the baby.
However, not only sex chromosomes but also some genes located on autosomes also plays a significant role in sex determination (but that is totally a different topic).
Cytogenetic techniques like karyotyping and FISH are employed to study the chromosomes. The process is known as karyotyping while the process of arranging chromosomes is known as a karyotype. A karyotype reveals so many things related to chromosomes.
Interesting article: 10 tips and tricks for karyotyping.
The male karyotype has one X and one Y chromosomes with 22 pairs of autosomes. The normal X chromosome is metacentric while the normal Y chromosome is acrocentric and smaller.
The karyotype of male is shown in the figure below. See first,
The Y chromosome is a unique identity for males. In comparison to other chromosomes, the Y chromosomes have fewer genes. An important gene for maleness that is the SRY is located on the Y chromosome.
The SRY gene is located on the TDS region on the short arm of the Y chromosome. Interestingly, not only the SRY but also some X linked genes and autosomal genes are involved in developing the male phenotypes.
If any abnormality in the Y chromosome happens, it causes serious reproductive and gender-related problems. For example, the deletion of some portion of chromosome Y or of the TDF or SRY region causes infertility.
Azoospermia is a common problem that occurs by the deletion of the Y chromosome. As we said, some genes located on the X chromosome are also associated with maleness, any abnormalities in it can lead to problems related to maleness.
By analyzing the male karyotype, abnormalities on the Y chromosome can be detected. Copy number variations associated with Y can’t be encountered usually, until and unless are bigger is size.
For instance, if 10 to 100kb of Y chromosome fragments got duplicated, it can be detected.
In another case change in the number of chromosomes also causes genetic abnormalities. For example, with X and Y sometimes another X chromosome also occurs, the condition is known as Klinefelter syndrome: 46, XXY.
Here the present on two X chromosomes causes infertility, intellectual disabilities, and developmental problems. Although the condition occurs totally randomly.
A karyotype of Klinefelter syndrome explained in our previous article. Read it by clicking the link.
Females have two X chromosomes instead of X and Y of males. Both the X chromosomes are the same in size and are metacentric. The typical normal female karyotype is shown in the figure below,
There is an interesting mechanism associated with female chromosomes- the X-chromosome inactivation.
As the females have two similar types of X chromosomes, one of the two is got inactivated totally, throughout their life to maintain the gene expression.
Let me explain to you in simple language,
Both the X chromosomes have the same genes in terms of number and function. The genes of a single X chromosome is enough for normal development. If it doubles, it causes severe problems.
Therefore, one of the two female X chromosomes becomes inactivated in order to regulate gene expression.
A female karyotype can’t show whether a chromosome is active or inactive but other structural abnormalities associated with it can be studied.
We should have to understand that if one X chromosome becomes inactive, still, its presence is very very important for normal female development.
If one X chromosome is not present, the condition known as monosomy causes serious gender related problems to females. The monosomy of X is known as Turner syndrome (46, X0).
The super female is developed by the presence of one extra X chromosome in a pair due to the event called nondisjunction. Notably, no serious health-related issues are associated with it.
Sometimes a large duplication of X chromosome results in X-linked acrogigantism. Either using karyotype or FISH the condition can be determined.
By preparing female karyotype both types of chromosomal abnormalities can be studied, still, a karyotyping technique is not powerful enough to notice smaller copy number various and SNPs.
SNPs are single base changes in a DNA that is also able to cause genetic abnormalities. SNPs on genes located on X and Y chromosomes are associated with infertility problems, besides chromosomal aberrations.
Related article: What is karyotyping?- Definition, Steps, Process, and Applications.
Using other techniques like PCR, DNA sequencing and DNA microarray SNPs and other small copy number variations can be reported. A female karyotype reveals the genetic abnormalities associated with males and females while the male karyotype reveals the genetic abnormalities only associated with males.
It is only a myth that problems related to X or Y chromosomes only cause reproductive problems.
Genes associated with mental, cognitive and intellectual development are also there on X chromosomes. However, genes can’t be encountered by karyotyping.