Tag Archives: genetics

Welcome To Holland

I am currently working through a FutureLearn on ‘the genomics era’. The course introduced some of the genetic errors that can happen in certain diseases.

One of the errors occurs when cells divide to form reproductive cells (sperm or eggs) – a process called meiosis. Most cells in the body have 46 chromosomes, arranged in 23 pairs. Reproductive cells have half the number, so that when a sperm and egg fuse, the newly fertilised cell has the normal complement of 46.

Certain diseases, like Down syndrome, Edwards syndrome and Patau syndrome, are the result of an extra chromosome in the fertilised egg. So instead of 23 pairs, there are 22 pairs and one triplet (or ‘trisomy‘). This error occurs when the reproductive cells are made, if the chromosomes of the parent cell are unevenly split between two new daughter cells.

The course featured a moving video of two parents whose daughter was diagnosed with Down syndrome. The father explains a powerful analogy to capture the emotions and experience of being told of such a diagnosis. The essay, ‘Welcome to Holland’ written in 1987 by Emily Perl Kingsley about having a child with a disability, is narrated in the video below, and is incredibly touching.

Parenting science: 12 top stories of 2012

It’s that time of year when we’re flooded with ‘best of’ lists, so allow me to jump on the bandwagon. 2012 has been a great year for science – the discovery of the Higgs Boson, the landing of Curiosity rover on Mars, and the ‘encyclopaedia of DNA’ that has given us the deepest insights into the human genome.

Here, I’ve picked out some of the stories that might interest parents, covering areas such as child learning and development, reproductive technologies, embryology, genetics, and even a bit of public policy thrown in. I’m sure I’ve missed some interesting ones too, so please add yours in the comments!

Mouse eggs created from stem cells for the first time (New Scientist)

Once a fully functional body cell develops from a ‘parent’ stem cell, it’s thought there is no going back to the previous state. A team of scientists in Japan, however, used a cocktail of signalling molecules to reprogram skin cells to become immature egg cells in mice (they had already done this to create sperm cells). What’s more, these cells could be fertilised and, in some cases, led to healthy mouse pups. This was a stunning feat of biological engineering that will help in the study of mammalian development and also hold promise in treatment of infertility. In a related story, controversy over whether biology textbooks need to be re-written took a turn when more convincing evidence was published that the number of eggs in a female isn’t fixed for her lifetime but can instead by replenished from a stem cell stock.

‘Chimera’ monkeys created in lab by combining several embryos into one (The Guardian)

The headline is pretty self-explanatory and the article itself is a fascinating read, so I won’t re-invent Ian Sample’s superbly crafted wheel. So if you want to know more about the controversial technique of creating normal, healthy monkeys with cells from more than one embryo and why it might benefit stem cell therapies, go read it! This may not be as bizarre and ‘unnatural’ as it first sounds, though, as we may all be walking chimeras and carry cells from siblings, aunts and uncles.

Genome Sequencing for Foetuses (Wired Science)

Being able to test foetuses for genetic faults that increase the risk of a serious disease, such as Down’s syndrome and blood or nervous system disorders, is hugely important. This is currently done mostly by invasive techniques such as taking samples of the placental tissue or amniotic fluid. This study, however, showed that it’s possible to work out the foetus’ genetic make-up by piecing together tiny fragments of DNA floating around in the mother’s blood. The ease of such a test would, of course, raise ethical issues about what is appropriate to screen for and what counselling parents would need, as well as requiring a firm and clear communication of risk.

DNA-swap technology almost ready for fertility clinic (Nature News)

Mitochondria are little energy powerhouses within most of our cells and they contain a small amount of their own DNA that is inherited wholly from the mother. A range of devastating diseases, that can affect the brain, liver, muscle and many other organs, are caused by defects in this mitochondrial DNA. A group of US researchers showed it was able to swap the mitochondria in a mother’s egg with one from a healthy donor to produce a normal looking embryo free from the mitochondrial genetic faults (restrictions on this technology would not allow a live birth). You can read about how the scientists actually did this in David Cyranoski’s article. And I would add that, contrary to some scare stories, these would not be ‘3 parent babies’ – mitochondrial DNA contains only 37 genes (involved in protein synthesis and biochemical reactions that make up respiration) compared with the many thousands of genes coded for by the DNA in the nuclei of our cells.

Babies are born dirty, with a gutful of bacteria (New Scientist)

Earlier this year I blogged about the “The microworld that lives inside you” and how the microorganisms that outnumber our own cells 10:1 are first transmitted from mum as a baby is born. A study by Spanish scientists, suggested that this isn’t the whole story. By studying the “meconium” – the baby’s first poo that is made up of materials ingested during the time in the womb – they detected two types of well developed bacteria. We don’t know for sure, but these were probably passed from the mother through the placenta. Our so-called “microbiome” is really important, because it influences our digestion, immune system, risk of disease, and maybe even our personalities.

Childhood stimulation key to brain development, study finds (The Guardian)

A US study provided more evidence that a sensitive period of learning and development exists early in childhood. They surveyed children from when they were four years old, recording details such as the number of books and the types of toys they had, to measure the amount of mental stimulation to which they were exposed. They also scanned the brains of the same children when they were between 17 and 19. As Alok Jha explains: “…the more mental stimulation a child gets around the age of four, the more developed the parts of their brains dedicated to language and cognition will be in the decades ahead.” Of course, this was an observational study and so limits the strength of the conclusions about whether the types of toys really caused brain developments, but the way the researchers tracked the same children over many years and the factors they took into account (parental nurturance had little effect, for example), was particularly impressive. Another cautionary note: the results were presented at a scientific conference and, as far as I know, have not appeared in a scientific journal, which means it won’t have yet been properly quality assessed by experts.

Golden ratio discovered in uterus (The Guardian)

At the risk of straying into mysticism, this was a nevertheless alluring report of a Belgian gynaecologist’s claim that the uterus represents an aesthetically pleasing “golden ratio”. This ratio is derived from something called the “Fibonacci sequence”, which is a sequence of numbers starting 0,1,… where every subsequent number is the sum of the previous two (so: 0, 1, 1, 2 , 3, 5, 8, 13, 21,…). The ratio between pairs of number in the sequence (divide one by the other) ends up being 1.618, which is the “golden ratio”. As Alex Bellos explains, its devotees believe it expresses aesthetic perfection and is found wherever there is beauty. According to Dr Verguts, when women are between the ages of 16 and 20 and at their most fertile, the ratio of uterine length to width is 1.6, spookily close to the “golden ratio”.

What happens to women denied abortions? This is the first scientific study to find out (io9)

Another set of results presented at a scientific conference, rather than in a scientific journal, but that is worth noting nonetheless. Annalee Newitz cites a Facebook post written by the lead researchers of a study that followed up women who had sought abortions at different abortion clinics in the US: “We have found that there are no mental health consequences of abortion compared to carrying an unwanted pregnancy to term. There are other interesting findings: even later abortion is safer than childbirth and women who carried an unwanted pregnancy to term are three times more likely than women who receive an abortion to be below the poverty level two years later.” Newitz further emphasises the preliminary results: “When a woman is denied the abortion she wants, she is statistically more likely to wind up unemployed, on public assistance, and below the poverty line.” If these findings turn out to be valid when further quality checks are carried out, they could help shape the debate on abortion policies and the state support a women seeking an abortion receives.

Boys and girls may be entering puberty younger (New York Times and The Guardian)

A study on the timing of puberty in boys by the American Academy of Pediatrics complements an earlier study on girls, which both hinted that puberty is, on average, starting gradually earlier in both sexes. Current estimates, at least for US children, are that the average age of puberty onset is around 9 years in black boys and girls and around 10 years in white boys and girls (although full sexual maturity may happen later than this). No one, as yet, knows why, but speculations include diet, changes in physical activity, improvements in healthcare, and chemicals present in the environment that affect our hormones.

Fathers bequeath more mutations as they age (Nature News)

A Swedish study concluded that a father passes on more genetic mistakes to their children than do mothers, and the older the man, the more mutations he is likely to pass on. This is most probably explained by the fact that sperm are generated from dividing ‘precursor’ cells throughout a man’s life and this cell division becomes less precise with age. Most inherited mutations won’t lead to any problems for the child, but the occasional one may increase the risk of a genetic disease like autism or schizophrenia. Taken together with rising average age of fatherhood, does this help explain, at least in some part, why autism rates are rising? (It could, but awareness and diagnostic changes are also likely to be at play). It’s not definitive and it shouldn’t scare older would-be fathers, but it may help in better informed decision-making.

An HPV Vaccine Myth Debunked (New York Times)

One of the arguments opposing vaccinating children against the Human Papilloma Virus (HPV), which can cause warts and cancer, is that in the minds of the young girls it frees them up to be sexually more promiscuous. Studying long-term medical data from girls in Atlanta, USA, however, showed no difference between vaccinated and non-vaccinated girls in pregnancies, sexually transmitted diseases, testing for sexually transmitted diseases, or contraceptive counselling. The article finishes by saying: “As one expert said, parents should think of the vaccine as they would a bicycle helmet; it is protection, not an invitation to risky behavior.”

Hungry mothers give birth to more daughters (Nature News)

Another eye-catching story was the report that during the Chinese Great Leap Forward famine, the proportion of boys being born dropped (from 109 boys for every 100 girls to 104 boys for every 100 girls). This sets up the tantalising possibility that sex ratios are adjusted in response to environmental conditions such as nourishment, a situation already known in deer where undernourished males tend to have fewer offspring than undernourished females (although in humans other factors like psychological and physical stress could be at play).

A final story that caught my eye was the latest results from the Avon Longitudinal Study of Parents and Children (ALSPAC), also known as the Children of the 90s, which probably warrants a blog post in itself. Nature News covered it and The Guardian’s sublime Science Weekly podcast featured it too (after 26:10). My favourite bit was how they collected the children’s milk teeth: “We had to negotiate for those. They are worth money to children, after all. In the end, we only got the milk teeth when we presented each boy and girl with an official Alspac form, signed by the tooth fairy.”

How sweet!

Uniquely you: Why babies are all different

I was listening to last month’s edition of Naked Genetics presented by Kat Arney, a podcast under the excellent Naked Scientists umbrella.

An interesting question was asked: if half the chromosomes come from a person’s father and the other half from the mother, why aren’t siblings simply identical twins born at different times? In other words, what mechanism controls individuality?

Dr Phil Zegerman provided a nice answer (listen from 25:04):


The transcript can be found here (‘Why are children all so different?’).

You can also watch this lovely animation of the process Dr Zegerman describes – meiosis:

And this is what it actually looks like in a fruitfly:

Do all babies start off female?

There was a bit of coverage last week in the scientific and popular press about some research that appears to refute the idea that the human Y chromosome could disappear at some point in our evolutionary future. In early mammals, the Y chromosome was the same size as the X chromosome but, during the course of our evolution has shrunk to a fraction of the size. This has led to the theory that the Y chromosome could disappear altogether if this shrinking carries on, but the new study has challenged this notion by showing that Y has, in fact, remained a fairly stable size over the last 25 million years. It seems that we may be arriving, or have arrived, at the bare essentials – the non-critical genes have been stripped away over time and natural selection has preserved the vital ones.

The jury’s still out on whether the Y chromosome will become extinct – “we won’t nail it without a crystal ball”, said Professor Darren Griffin of University of Kent in a Guardian article – but this sparked a memory of a conversation I had a while ago about what it is to be ‘male’ or ‘female’.

Some of wife’s friends had been debating whether or not all babies “start off as females”. This debate arose, I guessed while desperately trying to recall my high school biology classes, because of the fact that all fertilised embryos develop along the same path, regardless of the genetic make-up of the embryo. This is until certain genes on the Y chromosome (if present) are activated at around eight weeks and male-associated hormones, chiefly testosterone, are produced that act on some cells to start forming male-specific organs. Without these hormones kicking in, which is the case  in XX embryos when no Y chromosome in present, the cells in the developing embryo go on to form female-specific organs. This means that fertilised embryos under normal circumstances will develop female-specific sex organs unless a hormone cue is activated that signals otherwise.

So all embryos are female, then?

Hmm, perhaps not. One can still make a genetic distinction between males and females at the very point of fertilisation – XX chromosomes will give rise to females and XY will lead to males – and this remains static throughout an individual’s development (and, indeed, life). There are, however, some clinical oddities that throws some confusion into the mix. Some males, for instance, have two X chromosomes but develop as males instead of females because of the presence of a third, Y chromosome that contains the genes to provide the male hormone cues (“Klinefelter’s syndrome“).

So could we define maleness as the presence of at least one Y chromosome (some males are XYY too)?

Not really, because that definition comes unstuck when we consider individuals who are XX but develop as males (at least outwardly), due to the gene for the male hormone cue being copied to one of the X chromosomes (“XX male syndrome“), or individuals who are XY but develop as females, due to a defective Y chromosome (“Turner syndrome“) or mutated Y genes (“Swyer syndrome“).

This leads to complications when trying to enforce a purely genetic definition of gender. The International Olympics Committee for years attempted to enforce this view to adjudicate on cases of gender uncertainty, believing that this represented a more definitive and less intrusive test than physical examination. In this Y-centric definition, without ever meeting an individual and having only a few of their cells, the presence of the Y chromosome or any of its genes (such as the male sex determining gene called ‘Sex-determining Region Y’ (SRY)) would lead to the conclusion that those cells came from a man.

However, for the reasons I mentioned above about all the genetic uncertainties, pressure from a number of medical associations in the USA thankfully led to this sort of test being dropped by 2000. A ‘one-or-the-other’ test of this sort simply does not fully account for the complexities of gender and can lead to discrimination and unfair impediment. The lead opponent of such gender screening, Georg Facius, even proposed a ‘third gender’ for those that could be considered both male and female. One instance where this could be applicable is in cases of “Androgen insensitivity syndrome“, in which XY individuals show abnormal responses to the masculinising hormone androgen. Because the effects can vary, some individuals are anatomically male but have reduced fertility (mild), some possess ambiguous genitalia (partial), while some are almost indistinguishable from XX females (complete).

Even going back to the possible demise of the Y chromosome casts doubt on this Y-centric world. The experts that do anticipate the disappearance of Y are not predicting the end of ‘males’, rather they envisage another sex determining mechanism will take over. This happened before the emergence of the Y chromosome (sex was determined by environmental factors, such as temperature, and still is in some reptiles) and occurs in mammals where the Y chromosome has disappeared (in spiny rats, for example, the male-specific genes have hitched onto other chromosomes).

And this is all before we get into the complex world of gender identity, such as when an individual of one gender is uncomfortable being associated with that gender, which may be environment-driven (or may not be, or may be a little bit). Nor have I touched on psychological and behavioural differences, which lie on a continuous and overlapping spectrum between males and females and are often socially defined (and therefore subject to variation and change).

So none of this means that an embryo is female before the male signals kick in. It is perhaps more accurate to say that an embryo is gender-neutral, i.e. neither male nor female, until towards the end of the embryonic period, at which point anatomical differences start to become apparent in the foetus. But even then, as highlighted above, someone may share characteristics of both sexes and remain ‘double gender’.

Which is all a long-winded of way of saying that a binary male-female distinction is a little fuzzy.