Will your baby inherit her grandfather's feet, her father's elegant nose or your curly red hair? It's all in the genes.
He’s got Nkgono’s ears!” “Ooh, look! That’s aunty Lerato’s smile!” “No, no! He’s Palesa all over!” This could be a conversation that takes place around the hospital bed of any new mother.
For Mose Koena, who her new son looked like was blindingly obvious: “He’s the spitting image of his father,” she said. Indeed, parenting folklore says that newborns often very closely resemble their fathers, and this would seem to have a biological basis.
A mother always knows, of course, that the baby is hers; the child emerges from her own body, so there can be no doubt. But the father can never know with 100 percent certainty that the baby is his, so it would make sense for human evolution to favour children who resemble their fathers as a way of confirming the child’s paternity.
The only problem is, it’s not provable that newborns look more like their fathers. The only way to establish who a child looks like is to ask people their opinions and those are extremely subjective, as proven in two studies, one in 2000 and the other in 2007 (both published in the journal Evolution & Human Behavior).
In both, observers who weren’t related to either parent said that newborns actually looked more like their mothers than their fathers in the first three days of their lives – but the babies’ mothers said just the opposite, emphasising the child’s resemblance to the dad.
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How genes make us look and act
So how exactly do we end up looking like we do? “Our appearance is the result of the working together of many genes,” says Noelene Kinsley, a qualified genetic counsellor in private practice in Johannesburg.
“Even a simple feature like eye colour has a complex beginning and is determined by the combination of many genes and their products. But we know that the end result will be similar to someone in our family, as these genes have been passed through generations.”
Genes are made of DNA (deoxyribonucleic acid), which itself contains four chemicals, adenine (A), thymine (T), cytosine (C) and guanine (G), which are strung together in a particular sequence.
It’s the sequence of A, T, G and C that give the instructions for making things our body needs to function, such as enzymes to digest food, clotting factors to help form scabs when we cut ourselves, and the pigment that gives our skin its colour.
The strands of DNA, which carry the genetic information in the form of genes, are coiled together to form chromosomes.
Most humans have 23 pairs of chromosomes – a total of 46. Individual sperm and egg cells have 23 unpaired chromosomes each. So when a new human is conceived, it’s made up of half its mother’s genetic information (from the egg) and half its father’s (from the sperm).
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This genetic information then determines human characteristics, such as height or eye colour. Some characteristics come from a single gene, while others come from gene combinations.
And because every person has about 21 000 different genes, there are many possible combinations. For instance, more than a dozen genes interact together to determine eye colour – so when it comes to something as complicated as intelligence or personality, it’s impossible to pin them to one gene or a defined set of genes.
“It’s entertaining to play with the concept of trying to figure out what a baby will look like based on the parents, but the process is complex,” says Noelene.
Can your genes determine whether you’ll be a science whiz or a great soccer player? While genes do play an important role, your environment also influences your abilities and interests. “Just like appearance, there are other traits that are impacted by our genetics, including behaviour and intellect,” Noelene explains.
“The development of these characteristics isn’t simply the product of the genetic makeup but also a response to the environment. It’s a combination of genes interacting with other genes and the environment that moulds the character, and the outcome of this is obviously difficult to determine.”
The same applies to genetic disorders. More than 4 000 human diseases are caused by genetic errors or mutations, but having a genetic mutation that may cause a disease or condition doesn’t mean that it will develop into that disease or condition. Often, it takes several variant genes interacting with each other or with the environment to increase susceptibility to the disease.
Forewarned is forearmed
Naturally, most prospective parents would like to be able to rule out the possibility of a genetic disorder in their children, and genetic mutations such as those that cause cystic fibrosis (a lung disease) can be picked up by screening before falling pregnant (pre-pregnancy genetic testing), or during pregnancy (prenatal screening) for chromosomal disorders such as Down syndrome. But should all moms-to-be do this test? Not exactly.
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“Prepregnancy screening should be considered by couples who have a personal or family history of a child born with a birth defect, intellectual delay, hearing or vision loss, chromosomal abnormality or a genetic disorder,” says Noelene.
Prenatal screening is performed during pregnancy and includes ultrasound exams, maternal blood tests and a new test called noninvasive prenatal testing (NIPT), which tests the DNA of the foetus (which is present in the mother’s blood) to count the number of chromosomes present.
“The blood test and NIPT are used in combination with the ultrasound to identify the chance of a chromosome abnormality, in particular Down syndrome, Trisomy 18 and Trisomy 13,” Noelene explains. “If there’s a suspected high risk for one of these chromosomal abnormalities, it would need to be confirmed with an invasive diagnostic test, such as an amniocentesis.”
NIPT can be done from as early as nine weeks into the pregnancy. It costs about R8 000 and isn’t covered by medical aids. An option available to couples known to be at risk of having a child with a genetic condition is a procedure called preimplantation genetic diagnosis (PGD).
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Couples conceive through in-vitro fertilisation (IVF), outside the womb, after which the embryos are tested for genetic disorders such as cystic fibrosis, sickle cell disease, Tay-Sachs, Huntington’s disease and Down syndrome. Only the embryos that don’t contain the genetic disorder are implanted. PGD is available through some fertility clinics in South Africa.
There is concern that PGD will make it possible for prospective parents to predetermine characteristics of a child to suit their personal preferences – so called “designer babies”. This kind of genetic engineering presents all kinds of problems, both scientific and ethical.
However, this is not currently possible. Scientists still don’t quite know what every gene in the human body does and how they interact with each other; and no one knows what the long term effects of making smarter or more athletic children might be.
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