Are YY chromosomes possible?

Are YY Chromosomes Possible?

Two Y chromosomes are present in a chromosomal abnormality known as XYY or Jacob’s syndrome, however, only YY chromosomes in a genome aren’t reported to date.

X and Y chromosomes are two genetic material repositories significantly important for humans. The Y chromosome is present in males while the X chromosome is present in males and females. In females, it’s present in a pair. 

This article may help you to learn more on present topics: X and Y chromosomes. 

In layman, chromosomes are the place or building on which DNA or the entire genetic composition of a cell is placed. It’s a complex network of proteins and DNA, technically. 

Genes are polynucleotide chains of DNA (how scientific the line is!) and located on chromosomes. 23 pairs of chromosomes do humans have on which our whole genome is situated. Around 23,000 genes of the human genome are there only on chromosomes. 

The Y chromosome is one from the pair of sex chromosomes X and Y. Here in the present content I will answer the question, are YY chromosomes possible or not.

Are YY chromosomes possible? 

The Y chromosome is present only in males. It performs a significant function for developing male phenotypes, male secondary sexual characters and regulates gene expression of genes located on the Y chromosome. 

Genes and sequences like SRY and TFD regions, respectively, are very very crucial factors for the development of male gonads as they participate in varieties of reproductive differentiation and determination activities. 

Dysregulation of the SRY gene or abnormalities in TDF regions or AZF regions causes serious problems related to male sexuality. Infertility is a common cause of it. 

The Y chromosomes possess less genetic content and so fewer genes. But are tightly regulated. Only a single copy of genes (on a single Y chromosome) is sufficient to perform all these functions explained above. 

Now coming to the question what happens when another Y chromosome is present? 

In normal conditions, karyotyping studies suggest that one X and one Y chromosomes are present in males, when an extra Y chromosome incorporates into the genome, it becomes XYY. 

The structure of X and Y chromosomes.
The structure of X and Y chromosomes.

Read more:

  1. A karyotype of Edwards Syndrome- Explained
  2. A karyotype of Down Syndrome- Explained.
  3. A karyotype of Turner Syndrome- Explained.

XYY syndrome: 

Other names: XYY syndrome, YY chromosome, Jacob’s syndrome, 47, XYY syndrome or supermale. Previously, it was believed that a person with the present conditions is overaggressive and lacking empathy although it was just rumored. 

(nonsense science: people might though two YY cause overproduction of phenotypes related to it).

Technically, a person with an extra Y chromosome has learning and behavior problems (at some extend) but won’t have serious health conditions. 

Jacobs published the first report of XYY syndrome in 1966. The XYY syndrome is a condition known as aneuploidy in which one extra Y chromosome is present with a pair of X and Y. 

It occurs in males only with the frequency of 1 in 1,000 newborns worldwide. No severe physical symptoms are associated with the present condition. 

It occurs during the meiosis cell division of sperm cells through the event called nondisjunction in which the Y chromosome gets duplicated. When it participates in the embryo formation it causes a male fetus with extra Y chromosomes- the XYY syndrome. 

Note that the present conditions can’t be inherited, in addition, no clear reason for XYY to occur is to date reported. The symptoms and signs of the condition vary from person to person and age to age. Some common symptoms are: 

  • Weak muscle tone- hypotonia 
  • Dealy or underdeveloped motor skills and difficult speech. 
  • Mild infertility in some cases. 

Besides other scattered symptoms are autism, attention difficulties and learning disabilities. Scientific data suggest that a person with XYY syndrome can live like a normal person but they are a bit taller than others. 

Scientists use FISH and karyotyping techniques to diagnose the present conditions in which the karyotping is employed commonly. It’s a cheaper and trusted option. 

A blood sample or amniotic fluid/chorionic villi sample is extracted from a normal person or prenatal sample, respectively. Samples process to cell culture, harvesting and microscopy to investigate a karyotype. The expert prepares a karyogram and evaluates the final condition. 

Speech therapy, occupational therapy and Educational therapy are some treatment options available for XYY syndrome. 

Now coming to another important point of this section (i don’t know how to tell you about that but it’s important, trust me). Why the symptoms are so moderate? 

The reason is the inactivation of Y. When one of the two Y chromosomes gets transcriptionally inactive, the whole gene expression profile of the Y chromosome somewhat remains normal (the presence of another Y isn’t so noticeable). 

If another Y chromosome activates, it might create some serious problems, no related data are present. As I said, technically only a single copy from the set of the Y chromosome is required. 

Now it is yet not reported that in XYY, both Y chromosomes are transcriptionally active or not. 

Now coming to our main question are only YY chromosomes possible? What do you think? The answer is there in the X chromosome, let me explain. 

Very crucial and important genes for physical, cognitive and mental development which take part in various biological pathways and activities are present on the X chromosome.

Henceforth, the X chromosome is present in both males and females, however, in females, only a single X chromosome is transcriptionally active. 

So imagine, if an X chromosome is absent in males what will happen? 

It is not possible at all! No scientific data, literature, case study or patient report to date available showing the case of only YY chromosomes in males. 

Interesting article: XXXXY Karyotype- The Rarest Case of Aneuploidy.


Conclusively, I can say only YY chromosomes isn’t possible naturally but XYY syndrome might occur sometimes. These are all-natural events, occur randomly and we don’t know the exact reason behind that. But as per my opinion, all changes that nature tries should occur to make us survive- sometimes it works, sometimes won’t. 


What is a possible gender of the YY chromosome? 

The YY chromosome may present in males along with an X chromosome. The cytogenetic indication is XYY or also known as Jacob’s syndrome. 

What do YY chromosomes mean? 

The presence of an extra chromosome indicates that a person is suffering from a chromosomal abnormality known as a numerical chromosomal abnormality. 

What are the symptoms of YY chromosomes? 

Mild to moderate symptoms of an attention problem, infertility (sometimes) and taller that average are symptoms sometimes observed. 

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