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Asked by sarahsiddique to Lyn, Katy, Paul, PB, Ruth on 20 Jun 2013.
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Peter Balfe answered on 20 Jun 2013:
Many genetic disorders arise by mutation, so they’ll pop up in every generation whatever we do.
However most are recessive genes, which means the defective gene does you no harm providing your other copy is fine. Cystic fibrosis is caused by just such a defect. Now we have the human genome sequenced we’ve come to realise that most of us carry between 4 and 10 such defective genes on board, however the chance of us having children with someone with the same defect is tiny.
However some genes, such as CFTR, the gene “behind” cystic fibrosis have frequent defective versions, so these genes have a far higher chance of being in two people who have kids. As a result CF has an incidence of about 1 in 3,000 in the UK. These days we can screen couples for CFTR defects and give genetic counselling about this, consequently the number of CF babies born is slowly declining.
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Katy Brown answered on 20 Jun 2013:
I don’t think it would help. We’ve only very recently been able to cure some genetic diseases, and lots still can’t be cured, but they still exist.
There are lots of reasons for this, two of which Peter covered (new mutations causing the disease and people carrying one good and one bad copy of a gene, which sometimes has no effect). Another interesting reason is that sometimes although having two copies of a disease gene is bad for you, having one copy can be good. For example, there is a dangerous genetic disease called sickle cell disease, which is caused by a defective gene. People with two copies of this gene are very ill, but people who just have one copy are less likely to catch malaria than people with none. This means there is a balance between the advantages and disadvantages of the defective gene existing in a group of people, and in regions with malaria this works out so that the gene and the disease survive. -
Ee Lyn Lim answered on 20 Jun 2013:
Hmm…theoretically it would actually help. It might not completely eradicate the disease, because like Peter said sometimes genetic mutations just appear at random out of nowhere. It’s actually not that important whether someone with a genetic disease is treated or not, but if that person is *not allowed to have kids* (obvious ethical objections aside), then the copies of defective gene already in the gene pool would gradually decrease, and the chances of two defective copies coming together would be even lower. This is the basis of natural selection and evolution, where ‘weak’ genes are removed and the population as a whole becomes stronger.
This only applies to genetic defects that are inherited! Some genetic defects aren’t passed on, and occur regular because of some inherent property of our DNA. For example, every child born with Down Syndrome has an extra copy of chromosome 21. People with Down Syndrome can’t have kids anyway, and we don’t know what it is about chromosome 21 that makes them stick together – but it just happens. Sometimes there is a certain point in a chromosome that breaks more easily than the rest, so the chances of it randomly breaking at that point is much higher – that’s what happens in some types of leukaemia. That sort of thing can’t be eradicated.
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Paul Waines answered on 25 Jun 2013:
Hi sarahsiddique- thats a good question, and I can see why you might think that.
As Peter says, because mutations are always happening from one generation to the next, chances are that new conditions will continue to appear.
In some cases though, as we gain a better understanding of genetics and how these conditions come about, we may be able to reduce the number of people with these conditions.
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