He says the best place to put your carbon monoxide detector is either near your bed or your most dodgy gas appliance. This is because when carbon monoxide is in air, it won't rise up to the ceiling but will stay mixed in with everything else. Putting the detector near the most likely source or where you are most likely to suffer from carbon monoxide poisoning is the best plan of action. However, you do need to put smoke detectors near the ceiling because unlike carbon monoxide, smoke does rise.

Storm clouds have lots of tiny particles in them, and these are called hydrometeors. These are tiny particles of ice crystals. In the same way as if you rub a balloon on your head and it can stick to the wall because of static electricity, when hydrometeors bounce together, they rub charge on and off each other. This makes charge get carried up and down within the cloud. This creates a difference in charge across the cloud, creating an electrical field. The result of this is that the Earth has a different electrical charge to the cloud. When the charge difference becomes big enough, eventually the insulation of the air breaks down and you get a lightning strike. A lightning bolt carries between a billion and 10 billion joules of energy, which is enough energy to make 100 000 pieces of toast! The lightning bolt is sufficient to heat the air around it to about 30 000 degrees centigrade - that's about six times the surface temperature of the sun. When you make something that hot, the gas molecules get so excited that you literally rip them to pieces. The electrons in the gas molecules jump to a very high energy level and then jump back again to a normal energy level. When they do that, they give out light. The light that they spray out is what you see as a flash of lightning. The sudden extreme heating of the air causes a compression wave, like clapping your hands together, around the lightning bolt, and that's what slowly propagates to you as a roll of thunder. As light travels much faster than sound waves, that's why you see the lightning first and then you hear the thunder.

When you put crackers into a tin, the amount of air, and thus water in the air, is limited. Thus, even though they'll soak up some water, they don't have access to a whole room's worth of water, and so the amount of water available to make them soft and stale is minimal.

There are certain major genes, sometimes called Hox genes and sometimes called developmental genes, that switch on a whole suite of other genes. They are simply like switches in early developmental processes. To give an example that's a little bit closer to home, look for the nearest man and see how different you are from that person. Now although not everything that's different is down to one gene, the fact that you are female and he is male is down to a single gene called SRY. Very early in development, if SRY is present it makes testes, and if it's not, ovaries are made. So you've got just one single gene that switches over from one type to another, and then everything else follows from that, including the hormones produced by testes and ovaries. In worms, they've got a different set of these Hox genes, which start the whole process off. They're switching on a completely different set of genes in a different order, and so the developmental process is utterly different.

(Chris) This is one of these very interesting classes of diseases where pieces of DNA can change their length in an unpredictable way. There's a whole family of this type of diseases and they often affect the brain. This is probably because the brain expresses about 80% of the genes in our body. Therefore, if you have a problem with a particular gene, it will manifest itself in some way in the brain. With fragile X, we know that one part of the X-chromosome becomes longer than it should do, and it causes genes adjacent to the bits that get too big to behave a bit abnormally. Whether or not we are in the position to make any differences to those people very soon, I think the answers probably no.

(Mike) Fragile X is called a triplet repeat disease. This is because there are a specific three nucleotides, that's the A, T, G and Cs that Darren was talking about earlier, that repeat themselves a number of times. Everyone has this particular section repeated, but normally it's a limited number of repeats. You may have heard of the idea of the selfish gene. Well there's also selfish DNA. This is bits of DNA that try to replicate themselves and keep going not through the generations but within the cell generations in an organism. And so they make more copies of themselves, partly by unequal crossing over, and it's once you've passed a particular threshold of the number of triplet repeats that you get problems. The same is true of Huntington's chorea, and there are about four of these diseases.

There are two answers to this question. One is that there is only a single type of DNA, as it's all made up of the same basic codes. However, there are certain sub-types of DNA. These include cDNA, which stands for coding DNA, and single stranded DNA, which looks like a ladder cut in half.