How can mutations cause disease?
Sometimes, one of several DNA letters is accidentally changed for another letter. This mutation might possess a serious effect, or none at all.
If the letter T is swapped a great A in the codon GCT then the protein will still be the same, since both the old codon (GCT) and the new codon (GCA) code to the amino acid Alanine.
However, swapping an A for a T in a gene for haemoglobin causes a significant disease called sickle cell anaemia. Haemoglobin does the task of carrying oxygen around our bodies in the blood. In individuals with sickle cell anaemia, the sequence of proteins in haemoglobin is different, and for that reason it doesn't work as very well.
There are other types of mutations at the same time. Sometimes, a bit of the DNA sequence is missed out by mistake, or a new bit added in. Sometimes, parts of this sequence are swapped over, even between different chromosomes.
Inheriting mutations
Some of our genes is a copy through either our mum or each of our dad. If there is a mutation in one of these simple genes, this can be passed about from parent to child along with other gene. This is why ailments can run in families.
Small inherited changes might make big differences in our figures. For example, the most common mutation for you to cause cystic fibrosis - a problem where a person's internal internal organs become clogged with thick mucus - is the loss of three letters in a gene referred to as CFTR.
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