One of two sex chromosomes which determines the gender of the lifeform. The other being a X Chromosome.

The X Chromosome is appreviated "X" while the Y Chromosome is abbreviated Y.

In the alignment of XX the gender is female.
In the alignment of XY the gender is male. There isn't a YY allignment.

It is possible, under very rare circumstances, for a zygote to be conceived with YY sex chromosomes, but it can't survive very long because the X chromosome does lots of really important stuff for the foetal development. There are other sexes which can happen, such as XO and androgen-insensitive XY. And those chromosomes dictate sex, not gender. I have XY sex but female gender, thankyouverymuch.

The Y chromosome contains less genetic information than the X chromosome does. This is why certain types of genetic diseases, such as color blindness, affect more males than females. A female needs two copies of the defective gene to be afflicted, but a male only needs one copy on the X chromosome because the Y chromosome does not contain that genetic region to counteract the defective version on the X chromosome.

Another possible alignment is XYY. Occurs in 1 in 1000 live-born males. They are phenotypically normal, taller, have severe acne, and normal intelligence. 1-2% have antisocial behavior but are not violent.

Advances in medical science have allowed geneticists to map out the ever-finer details of the mysterious Y chromosome. Femigeneticists the world over have been astir over the recent discoveries of the following gene loci, which has previously been observed for centuries but, up to now, have never been associated with genetic or environmental factors in the male Homo sapiens species.

This is how some believe the Y chromosome is coded...

  • Testices Determining Factor (TDF)
  • Three Stooges Appreciation (Curly stimulation Factor, CSF)
  • Gadgetry (MAC-locus)
  • Channel Flipping (FLP)
  • Catching and throwing (BLZ-1)
  • Self Confidence (BLZ-2) (notably unlinked to ability)
  • Ability to remember and tell jokes (GOT-1)
  • Sports page (BUD-E)
  • Addiction to death and destruction movies (T-2)
  • Air Guitar (RIF)
  • Ability to identify aircraft (DC-10)
  • Preadolescent fascination with Arachnida/Reptilia (MOM-4U)
  • Spitting (P2E)
  • Sitting on the toilet reading (linked to Sports page gene)
  • Inability to express affection over the phone (ME-2)
  • Selective hearing loss (HUH?)
  • Total lack of recall for dates (OOPS)
This is straight from Bio Anthro class.
I think it needs to be mentioned here that we're talking about humans. Remember, we're not the only species on the planet? Birds, for example, have their Y chromosome in the female of the species. Some animals have their male as a haploid organism, and the female is diploid. In most angiosperms, gender differentiation doesn't even occur until the flower is formed, and even then, it's only a matter of turning on or off a few genes. In yeast, gender is determined by one gene located on chromosome three; there are also spare copies of both gender type genes that are silenced, but can be activated by a recombination event. (So yes, you can change the gender of your yeast.)

Naturally, though, since most genetic studies have gone on in organisms in which the norm is XX-females and XY-males (mainly humans and fruit flies), we tend to think of the Y chromosome as the male chromosome.

Population Genetics

The Y chromosome, as has been stated above, is passed from father to son directly with minimal genetic re-combination. Therefore a sons Y-chromosome will be identical to his fathers and his grandfather etc. etc. Therefore a view of inheritance can be built up by looking at the non-recombining section of the Y-chromosome.

This can be used in the same way as mtDNa because like mitochondria, there is no recombination between generations. It also gives the other half of the story i.e. tracing the paternal line (maternal lines have been studied much more extensively up to the present date).

The main advantages of this approach are that the Y-chromosome is much larger than mitochondrial DNA, and has a slower mutation rate. This allows the analysis of very deep branches (in time) with relative accuracy, which may not be present in mtDNA analysis due to reverse mutations leading from the higher mutation rate present in mtDNA.

The resolution of detail within the y-chromosome has recently been greatly improved by the introduction of denaturing high-performance liquid chromatography (Richards + Macaulay, 2001), which also increases its expense.

Future work in to population genetics is likely to comprise mainly of Y-chromosome studies, due to a lack of past work. This is mainly due to the ease of mtDNA analysis compared to Y-chromosome analysis, but now the gaps of knowledge left must be filled.

A sex chromosome found in humans, fruit flies, and certain other animals where the male is the heterogametic sex. The Y chromosome causes the individual to become male in most mammal species and carries few other genes besides those dictating sperm development and triggering appropriate hormonal output.

It is part of the XY set of sex chromosomes, where the male has only one X chromosome and usually a Y chromosome (fruit fly males can also have just one X and nothing else), and the female has two X chromosomes.

From the BioTech Dictionary at For further information see the BioTech homenode.

The Y chromosome, the sex chromosome found in male humans, was long believed by scientists to be nothing but a useless genetic wasteland, useful only as a trigger to start the fetal development that makes a male embryo develop the male primary sex characteristics. All human embryos develop according to a basically female template until a certain point, after which the presence of a Y chromosome may cause the embryo to start developing male traits. It isn't the whole Y chromosome that triggers this development, only a gene named SRY, and it was long held that this gene was the only important gene located on this tiny (approximately half as large as its X counterpart) chromosome. The rest of the chromosome consists of largely repetitive DNA, and it was widely believed that this was because genetic erosion had slowly destroyed the chromosome over the millenia it has existed, and that it (and therefore human males) was threatened with extinction. Some pop science journalists speculated that the species would have to develop human cloning to survive in a future setting where the species would consist only of females.

The little bastard turned out to trick them all. During a recent mapping of the Y chromosome, several fascinating phenomena were discovered, including the reason why so much of it consists of repetitive DNA strands. It turns out that most of the genetic information encoded on the Y chromosome has to do with sperm production, although a few other functions and traits are encoded there as well. A little background is in order here: Most chromosomes in human cells are autosomes, that is, chromosomes that come in pairs. Of these pairs, one chromosome is passed down from the person's mother, the other from the person's father. This holds true for all non-sex chromosomes as well as the X chromosome. This pairing of chromosomes is useful because it allows the chromosomes to exchange some genetic information; a process that has the dual function of allowing them to recombine genetic material during the creation of egg and sperm cells (improving genetic variation within the species), and also allows a form of genetic repair in which bad genes on one chromosome are swapped out with a copy of good genes from its neighbour. Unfortunately for the Y chromosome, it has no such compatible neighbour. Its very tips match its X chromosome counterpart (male humans have a X chromosome as well as a Y, while female humans have dual X chromosomes), but any similarity ends there. The middle of the Y chromosome is like no other human chromosome, barring it from exchanging genetic material from other chromosomes.

This is why it was widely believed that the Y chromosome was useless, eroded and dying: It was widely held that there was no way it could repair any genetic damage, and that as the generations passed, the chromosome would degenerate until the point where even the SRY gene would be destroyed, wiping out the human male. However, nature turned out to be a clever engineer: The genetic makeup of the middle part of the Y chromosome turns out to be a gigantic tangle of genetic palindromes, allowing it to copy itself when bad genes are found. The characteristic shape of the Y chromosome, with the slight curve at its middle, is in fact a reflection of this; a gene on one side of the curve can copy parts from its twin the other side. The longest palindromic string of chemicals is 3 million bases long -- a bit more impressive a palindrome than "Otto". Since the Y chromosome does not ever copy any genetic material from other chromosomes, a man's Y chromosome is an exact copy of the one his father had, his grandfather before him, and so on for countless generations.

Unfortunately, while the Y chromosome's self-repair mechanism keeps it from deteriorating into the useless waste it was once believed to be, its nature also leaves it vulnerable to mutation, and indeed the most common reason for male infertility is deletions on a Y chromosome..... but obviously, such a flawed Y chromosome won't be passed on.


As an aside, there's no natural law that states that the XY combination must belong to a male within a given species, that's just how it is for mammals. Birds develop in a more or less completely opposite manner than mammals; their females have the XY combination and their males have XX. Reptiles don't have sex chromosomes at all, the sex of a reptile is determined by the temperature in its egg early in its fetal development.

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