Y Chromosome

‘With about 60 million building blocks, the Y chromosome is the smallest of the 46 chromosomes in the human body.’ BBC News online

‘Most mutations occur in males. It's about a two-fold difference. One suggested reason is the larger number of cell divisions in the male germ line (sperm).’ Wellcome Trust

‘The mutation rate is about twice as high in male as in female meiosis, showing that most mutation occurs in males.’  "International Human Genome Sequencing Consortium" International Human Genome Sequencing Consortium, Nature, 2001

‘Photos of our chromosomes graphically illustrate the demise of the Y chromosome. Compared with monsters such as chromosome 1, it is tiny, dwarfed by its former partner, the X. Is the Y chromosome destined for oblivion?’ Wellcome Trust, 2003

‘The mammalian Y chromosome is thus likely to be engaged in a battle in which it is outgunned by its opponent. A logical consequence is the the Y should run away and hide, shedding any transcribed sequences that are not essential to its function.’ Philosophical Transactions of the Royal Society

‘The absence of recombination with a homologous partner means that it can never be 'repaired' by recombination. This has led to suggestions that the Y is destined for extinction – it will eventually dwindle to nothing. According to this model, its role in sex determination will eventually be taken on by genes elsewhere in the genome. That may seem hard to imagine, but the XY method of sex determination is far from universal. In fruit flies the ratio of X chromosomes to autosomes is crucial. In crocodiles and other reptiles, chromosomes have a marginal role – the temperature at which eggs are incubated is key. Slipper limpets, which form stacks attached to seashore rocks, change sex according to their position in the stack. Even more bizarre is the marine worm, Bonellia viridis. Its larvae settle on the ocean floor and turn into 10-cm long females. Other larvae are attracted to the worm's proboscis, and when they land on it they are ingested and turn into tiny sperm-producing symbiotic males in the female gut. Perhaps a more likely glimpse of the future of humans comes from obscure mammals in which SRY and the Y have already been superseded. The Armenian mole vole, for example, has diverged into two species, one of which survives without a Y or SRY. In some South American field mice and the Scandinavian wood lemming, XY females are commonplace. In the lemmings, a gene on the X chromosome can overpower SRY, when present, making embryos female. Professor Jennifer Marshall Graves, an expert in comparative genomics and mechanisms of sex determination at the Australian National University in Canberra, believes these oddities hint at the destiny of the human Y. "The rodents," she concludes, "are leading us into the new era of a Y-less existence." A more optimistic interpretation is given by Professor David Page of the Whitehead Institute in Cambridge, USA, who led the team that sequenced the human Y chromosome and studies the genetic mechanisms underpinning human sex determination. Sequencing has revealed just what a mishmash of odd features the Y chromosome is, rich in repeats and with its DNA constantly shuffling around. Professor Page believes one oddity – a pair of large palindromes, identical repeats arranged in opposite orientations on the chromosome – may provide a mechanism to safeguard Y sequences.

Rather than swapping DNA with the X, the Y may exchange DNA with itself, in a recombination process mediated by the palindromes. The palindromes contain genes, so in effect the Y could be able to repair itself, replacing bad sequence with good. It's not all over for the Y chromosome just yet, suggests Professor Page. Not everyone is convinced, however. As Mark Jobling points out, the evolutionary cost of this mechanism is high: bad sequence may overwrite good, spreading mutations that cause infertility. So, is the Y here to stay or are we going to go the way of the mole vole? Or, more intriguingly still, might both scenarios come to pass – could we end up going down divergent evolutionary pathways, with the creation of separate human species?’ Wellcome Trust, 2003

How delicious such redundancy

How delicious such redundancy - poetic justice

for the unjustified superiority muscle provided;

physical strength outweighing better grey cells -

collective culpability for the long ruin of women;

their pride and talent, right to equal social power -

for the ruin of Earth, despoilation of Mother Nature

because of her flowered frock, her lack of weapons -

becoming extinct, like tigers; entering some darkness

designed for destroyers - returning to seed potential

among incandescent stars. Millennia, life dreaming

to create the flower, now beginning again with Man,

the squandered male - patiently guddling fresh earth

for creative molecules to execute her intended principles.

Or a reprieve granted - thanks to the hearts of good men.

‘The DNA sequence of the human Y chromosome - the 'maleness' chromosome - has been published. In the biological battle between the sexes, the Y chromosome has suffered defeat after defeat. The male-determining chromosome has seen its gene supply shrink from more than 1000 genes when sex chromosomes first evolved, to what scientists once thought was only a handful of genes, a downward trend predicted to continue until the Y disappeared altogether. But two studies presented on 18 June 2003 and published in the journal Nature suggest that the rumours of the Y's demise have been greatly exaggerated. Researchers from Whitehead Institute for Biomedical Research in Cambridge, Mass., and Washington University School of Medicine in St Louis found that not only does the Y contain far more genes than scientists thought – the team found about 78 genes – it also includes a large number of genes arranged in pairs along this single chromosome in ways that may allow the Y to mimic the paired chromosome structure of the rest of the genome. The researchers suggest that this arrangement may help the Y chromosome repair injured genes without the benefit of sexual recombination – the method of gene repair used by all other chromosomes. It's an elegant system that would debunk the theory of a 'rotting Y' – the widely held notion that the male chromosome and its dead or dying genes will continue to rot away over the next 5 million years until there's nothing left.’ Wellcome Trust, 2003

Man Creature under Threat

He does not realise himelf under threat -

the Man creature; like tiger or Polar Bear.

He also ignores his own plight - his first spark

is going out; fizzing sparkler on a damp night

among mist, his small star is burning to the metal,

spluttering in the hand of life, in the gloomy dark.

His glitter is mightily spent, his species in retreat;

yet he thinks himself indispensable, irreplaceable.

But Nature laughs among grasses, and flowers

nod, daffodils giggling – she has found a way

for all things, infinitely adaptable to any end

men might race towards - she is waiting still

with her wand; at every last spiral of DNA,

she passes her organic power - a molecular

magic - shuffling the supremely plastic genes,

storing commodities, letters, codes, chemicals

for new identities.Yes, she will do without him -

if she must; despite her long support in generous

hope of some improvement - genetic lessons

for care of the garden, all his fellow creatures.

‘Scientists have deciphered the make-up of the Y chromosome, the bundle of DNA that defines the male. We can start trying to figure out how the presence of these genes controls the development to become a male. The genetic data will help researchers understand the causes of male infertility, as well as the evolution and function of the Y. It turns out that large chunks of the DNA sequence are multiple repeats of seemingly meaningless stretches of genetic code. Buried within these regions are genes that are essential for male development, including the master switch that "makes" a baby boy. The work was carried out as part of the international human genome sequencing effort, largely by US teams. John McPherson of the Genome Sequencing Centre, Washington University School of Medicine, St Louis, Missouri, US, said the genetic map of the Y would help researchers find clues to what makes a male. "It gives us a complete catalogue of all the genes and we can start trying to figure out what the function is and how the presence of these genes controls the development to become a male," Dr McPherson told BBC News Online. "We're a long way off from understanding everything but we now have the catalogue that we can look at, and these are the triggers that trigger a whole series of events in development." With about 60 million building blocks, the Y chromosome is the smallest of the 46 chromosomes in the human body. As well has helping researchers investigate the genetic basis of male infertility, the data on the Y will be useful in tracing the roots of male ancestry. The Y chromosome is passed, almost unchanged, from father to son, but tiny variations, known as polymorphisms, occur gradually over time. This gives geneticists a tool to look back in history and trace man's earliest paternal ancestors. The Y chromosome sequence also throws light on an ancient biological battle of the sexes between the female, X, chromosome and the male, Y, chromosome. Males have one X and one Y chromosome, whereas females have two Xs. Occasionally, genes on the Y chromosome are "overwritten" by similar genes on the X chromosome. The tracts of repeated sequences on the Y chromosome may be necessary to ensure that essential genes are not lost in this battle with the X.’ Helen Briggs, BBC News Online

Self-fixing Y Chromosome

Self-sorting, self-fixing, unilateral repair;

emotional pattern reflecting the physical -

different to all other chromosomes, yet intimately

connected, dependent; perversely self-sufficient -

lonely in the Genome; self-editing, asking nothing -

just quietly being male, mending sperm production.

He’s shrunk

He’s shrunk, curtailed communication;

wanting to solve all his own problems -

as everything else throws out chemical

arms, he has made himself - sufficient,

copied his essential elements, even backwards -

but nothing must bar his essential independence;

he will need no-one, mating just servicing

this drive for reproduction - survival of Y.

‘The very different strategies of sperm and eggs…in animals and many other creatures as well, the sperm is as streamlined and cut down as it seems feasible to be. It has a head, which constists virtually entirely of a nucleus enclosed in membranes; a tail, which drives it along; a ‘middle piece’ between the head and the tail, which contain a few mitochondria to power the tail; and an ‘acrosome’ at the front, a kind of nose-cone, which produces enzymes that enable it to penetrate the egg. The mature sperm contains almost no cytoplasm and supplies virtually zero nourishment to the embryo that it helps to form. It is a mobile packet of genes with a corrosive nose: a genetic missile.’ The Facts of Life Revisited, Ian Wilmut and Keith Campbell, The Second Creation, Headline, 2001

‘The mutation rate throughout the genome is about five times high in men as women because of the repeated replication needed to supply fresh sperm cells throughout life. ‘X is the odd one out, the misfit. Its pair, the chromosome with which it has some affinity of sequence, is not, as in every other case, an identical chromosome, but is the Y chromosome, a tiny and almost inert stub of a genetic afterthought… Three quarters of all sex chromosomes are Xs; one quarter Y. Or, to put it another way, an X chromosome spend two-thirds of its time in females, and only one third in males. Therefore, the X chromosome is three times as likely to evolve the ability to take pot shots at the Y… the result has been that the Y has shed as many genes as possible and shut down the rest to ‘run away and hide’. So effectively has the human Y chromosome shut down most of its genes that the great bulk of its length consists of non-coding DNA, serving no purpose at all – but giving few targets for the X chromosome genes to take aim at…’ Matt Ridley, Genome: The Autobiography of a Species in 23 Chapters, Fourth Estate, 2000

‘A tiny and almost inert stub’

Trust us superior Xs to get lumbered with “a tiny and almost inert stub” -

“A genetic afterthought” - “a stump”, a simpleton - as partner, mate;

That chiefly programmes for liking cars, breasts, gadgets, going down the pub -

Yup, married to a wee cowerin, timorous beastie of a chromosome is our fate.

In fact most of it “serves no purpose at all” - just long stretches of junk DNA,

Which will come as no surprise to us women, of course,

Who’ve found most men a complete waste of space, (except perhaps when they pay),                           

Given as they are to abandonment, aggression, competition, and if all else fails, force.

But this unexpected boost from science is heartening, comes as great relief -

Where it really matters, we’re not only stronger, feistier, cleverer, but bigger -

So the next time a man tries to make you feel small, gives you grief,

Just think of the tiddly size of his chromosome - and snigger.

‘A gene that has always been in a Y chromosome since the origin of mammals…will have experienced male bodies of many different species, but never a female body of any kind.’ Richard Dawkins, Unweaving the Rainbow, Penguin, 1998

Distillation of the alien male

Distillation of the alien male;

the sinewed, muscled one -

boom and drum; mud turning

into rumbling barritone throat -

or ingenious primaeval mechanism;

coiled heat, lust, blood-rush-flush -

invisible cantilever, simple penis key -

eager semen; that caveman exhaustion.

The haired one. Still woolled,

smelling of earth, grass - wolf

in sheep’s jeans, hunter in pinstripe

skins, his bare feet stuck with leaves,

needles - even in shiny-hide shoes,

he still dances at night, hooved.

How will his heart be found

in dissected red-raw meat -

still pumping adrenalin

in exposed molecules -

(while the ladies have tended,

watered the rose in the breast),

a rusty crust of unspoken words

hurting; unshed tears calcified -

stalactites in the red chamber,

always dripping, inching on -

like white sheet ice draping his art,

spreading through the unused rooms.

‘[Darwin] emphasized that, though in almost all species the female was the choice-maker, in human societies the privilege of choice making had passed to the male, with deleterious effects.’ Gillian Beer, Introduction to the Origin of Species, 1859, Oxford University Press, 1988, (regarding Darwin’s, The Descent of Man, 1872)

‘And Adam called his wife’s name Eve; because she was the mother of all living.’ Genesis 2, The Bible

‘Scientists in the US have published the results of their detailed scrutiny of the genetic sequence of the human Y chromosome. This DNA bundle - one of 24 distinct chromosomes found in human cells - holds the crucial information to make the male of our species. The work is part of the enormous job of following up the data that came out of the international Human Genome Project (HGP)…declared complete in April. Any attempt to make sense of the data inevitably involves large-scale computing effort, but, by any standards, annotating the Y chromosome was a huge task. "It's one thing to generate the sequence and its another to go on to discover which bits are functional and what they can tell us about disease and evolution," explained Mark Ross, head of the Wellcome Trust Sanger Institute's project to analyse the X chromosome near Cambridge, UK. The Y chromosome contains a great many repeated sections of DNA and far fewer genes, letter for letter, than other chromosomes. Francis Collins, director of the US National Human Genome Research Institute, said in Washington DC on Wednesday that the Y was the fifth chromosome of the completed human genome sequence to undergo detailed analysis. "The Y was the most challenging - the most difficult chromosome," he said. The scientists found 78 genes in total on the Y, many but by no means all of them to do with sperm production. One is the sex determining gene, the "master switch" that makes a baby boy; another is a gene that has some sort of function in the brain and is not found on the female X chromosome. For every million letters of genetic code they looked through, the researchers found only three genes, far fewer than the 10 per million average throughout the rest of the genome. The chromosomes in the nuclei of our cells are arranged in pairs... Researchers say the chromosomes draw on their mate to carry out repairs to genes that suffer mutations through disease or replication errors. But the Y cannot do this with the X, and it therefore carries backup copies of important genes within itself. It will use one copy to fix a flaw in another - a process called gene conversion. Dr David Page, from the Whitehead Institute in Massachusetts, who led the team deciphering the Y chromosome, said: "The sex chromosomes represent a grand experiment of nature. In our work, every few years we've caught a glimpse of some unexpected aspect of this experiment. And of all these aspects, this Y-Y gene conversion is one of the wildest." Dr Page said it was probably when this gene-fixing technique went wrong that some male infertility problems arose. He said doctors were already using his team's data to understand the genetic origins of male infertility. He added that genes on the Y might play a role in influencing gender-specific differences in disease susceptibility.’ BBC Science, 2003

Perhaps it is the fear of inferiority that makes men fear equality

Perhaps it is the fear of inferiority that makes men fear equality.

Found wanting now in the gene department, scoring an average

of three genes per million letters - compared to the average ten

in the rest of the Genome; oh, dear, not feeling quite so superior

now, are we - just because we can open jars, punch harder, drink

more beer, put up IKEA shelves, programme the DVD - big deal.

And no wonder men seem so obsessed with their willies - protecting

scrotums like a supple, extortionate Burberry handbag slung bulging

with two precious golden eggs - so many genes developed for sperm

production, reproduction, expulsion - so weird really, these wrigglin’,

jigglin’ little tadpole squiggles, swimming in the Testicle Sea - as if

each one its own wee manic creature; single-minded, simple-minded.

With just one goal – to deliver its manuscript cargo at all costs; sent forth

on a fountain into neverending tunnel, where all must perish on the quest -

bar one, who just might score the mythical, mapless treasure, headbut egg;

or all bang bonces on a plastic bag, dying amid fish-skins, tea bags - holey

tights. And what about that weird one – a gene with “some sort of function

in the brain”, not found in the X. It’s got to be - explanation for fascination

with bloody cars, driving fast; tinkering, polishing - envy - car magazines

Or obsession with sport; grossly overpaid bumble-thigh men kicking balls.

And what about this ‘gene conversion’, relying only on the self for healing,

when all the others have a mate, best friend, close partner; how sad is that?

(maybe the male heart reads the Y chromosome); or making backup copies

of your most important parts in case of trouble - is that why they remember,

sensibly, to back up their own work, and avoid ending up in floods of tears?

Understand computers better? - (or all the boring bits anyway beyond Word,

email, eBay and other shopping); sounds quite like having imaginary friends,

invented girlfriends to me - and to think they call women pathetic... At least

they can now blame their genes instead of their mothers – and one last thing;

if this ‘gene conversion’ fixes flaws, why are men, in general, so imperfect?

Note from the author
exploring the project

    Gene Story
    Romantic Science
    Some Special Genes
    X & Y
        Y Chromosome
        SRY Gene – Master Switch
        Sex Wars
        X Chromosome
        Some notes on the
        Gender of Science

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