Y Chromosome


Much smaller than the X chromosome and contains many fewer genes.

The Y chromosome is one of two sex chromosomes.

The other is the X chromosome.

Y is normally the sex-determining chromosome, since it is the presence or absence of Y that typically determines the male or female sex of offspring produced in sexual reproduction.

All human men descend from the paternal line are from a single man dubbed Y-chromosomal Adam.


Adam lived probably between 200,000 and 300,000 years ago.

It is entirely coincidental that the Y chromosome, during mitosis, has two very short branches which can look merged under the microscope and appear as the descender of a Y-shape.

The Y chromosome contains the gene SRY, which by default triggers male development.

The DNA in the human Y chromosome is composed of about 59 million base pairs.

It is passed only from father to son.

It is one of the fastest-evolving parts of the human genome.

Over 200 Y-linked genes have been identified.

All Y-linked genes are expressed and hemizygous , except in the cases of aneuploidy such as XYY syndrome or XXYY syndrome.

Its presence or absence determines the gender.

Males have one Y chromosome and one X chromosome.

Females have two X chromosomes.

The Y chromosome contains a gene, SRY, which triggers embryonic development as a male.

The Y chromosome contains other genes needed for normal sperm production.

Some men have two Xs and a Y (“XXY” Klinefelter syndrome), or one X and two Ys (XYY syndrome), and some women have three Xs or a single X instead of a double X (“X0”-see Turner syndrome).

95% of the Y chromosome is unable to recombine, as only the tips of the Y and X chromosomes recombine.

It is estimated, the human Y chromosome has lost 1,393 of its 1,438 original genes over the course of its existence, a rate of genetic loss of 4.6 genes per million years.

The Y chromosome is passed exclusively through sperm, which undergo multiple cell divisions during gametogenesis.

Sperm are stored in the highly oxidative environment of the testis, encouraging further mutation.

The Y chromosome is at a greater risk of mutation than the rest of the genome, as a factor 4.8.

The Y chromosome is particularly prone to the accumulation of junk DNA.

About 13% of men with azoospermia have a defective spermatogenesis that is linked to defects of the Y chromosome.

Defects of the Y chromosome tend to be de novo micro-deletions and affect usually the long arm of the chromosome. 

A section of the long arm of the Y chromosome has been termed Azoospermia Factor (AZF).

At Yq11 and subdivided into AZFa, AZFb, AZFc and possibly others.

Defects in this area can lead to oligospermia or azoospermia.

Through sheer random assortment, an adult male may never pass on his Y chromosome if he only has female offspring.

The Y chromosome spans about 58 million base pairs and represents approximately 1% of the total DNA in a male cell.

The Y chromosome contains over 200 genes, at least 72 of which code for proteins.

Traits that are inherited via the Y chromosome are called Y-linked, or holandric traits.

Some cells, especially in older men and smokers, lack a Y chromosome.

Loss of the Y chromosome can be detected in almost half of men who are older than 70 years of age.

Men with a higher percentage of hematopoietic stem cells in blood lacking the Y chromosome have a higher risk of certain cancers and have a shorter life expectancy.

Male smokers have between 1.5 and 2 times the risk of non-respiratory cancers as female smokers.

The Y chromosome is normally unable to recombine with the X chromosome, except for small pieces of pseudoautosomal regions at the telomeres, which comprises about 5% of the chromosome’s length.

The human Y chromosome is gene poor.

Genes encoded on the human Y chromosome include:

Diseases linked to the Y chromosome typically involve an aneuploidy, an atypical number of chromosomes.

Y chromosome microdeletion genetic disorders is caused by missing genes in the Y chromosome.

Y chromosome microdeletion may result in no symptoms and lead normal lives in affected men

Y chromosome microdeletion is also present in a significant number of men with reduced fertility or reduced sperm count.

Klinefelter syndrome (47, XXY) is a condition of having an extra X chromosome, which usually results in defective postnatal testicular function.

47, XYY syndrome, known as XYY syndrome, is caused by the presence of a single extra copy of the Y chromosome in each of a male’s cells.

An extra copy of the Y chromosome is associated with increased stature and an increased incidence of learning problems in some boys and men, but the effects are often minimal.

There is an elevated crime rate among individuals of XYY males which is due to a lowered median intelligence and not to an increase in aggression.

Increased height is the only characteristic reliably associated with XYY males.

Having more than one extra copy of the Y chromosome in every cell is rare.

The extra Y genetic material in these cases can lead to skeletal abnormalities, decreased IQ, and delayed development.

XX male syndrome occurs when there has been a recombination in the formation of the male gametes, causing the SRY portion of the Y chromosome to move to the X chromosome: the development will lead to a male, because of the SRY gene.

The Y chromosome is passed exclusively from father to son, on the patrilineal line.

Mitochondrial DNA is maternally inherited to both sons and daughters, and is used in an analogous way to trace the matrilineal line.

Male fetal progenitor cells could persist postpartum in the maternal blood stream for as long as 27 years.

Y chromosome has been identified in multiple areas of the brains of deceased women.

Frequently with age, cells are missing the Y chromosome.

Studies have linked loss of the Y chromosome in blood to cancer, heart disease, and other disorders.

Blood cells’ loss of the Y chromosome in a subset of cells, called ‘mosaic loss of chromosome Y’ affects at least 40% of 70 years-old men to some degree, contributes to fibrosis, heart risks, and mortality.

Estimated that 20 percent of men in a large genetic database have lost Y chromosomes from some detectable proportion of their blood.

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