OCR A Level Biology Mitosis Practical

hey has anyone done the mitosis practical 1.1
our college just expects us to work independently, so im rlly confused about how to record the chromosome lengths
one of the teachers said that the chromosome length will be double what we see on the microscope in anaphase or telophase? im so confused
is this the same for metaphase as well?
id really appreciate anyone helping out lol thanks x

It seems to me like there has been some confusion in the instructions. You don't need to double the length of a chromosome, but what your teacher might be getting at is that during anaphase and telophase the chromosomes have a 'V' shape as the spindle fibres shorten to move the chromosome to different poles of the cell. You can't really measure both legs of the V shape using a graticule, but you can measure one 'limb' and double it to get the total length. This would be the same for metaphase too, if you can distinguish individual chromosomes.

Another part of the issue here may be that you are used to seeing pictures of all the chromosomes (karyotype) all laid out neatly according to size, and it looks quite easy to measure them in this way. In a real cell the chromosomes look a lot messier or are not straight, and are not easy to distinguish. This makes it difficult to get a straight line measurement.

I would suggest remembering an approximate size for chromosomes, since this can make it easier to spot if you have made a measurement mistake. Bear in mind that chromosomes in the nucleus when visible during mitosis are highly coiled so you are not measuring their full length. If the nucleus of a human cell is on average around 10um, the chromosomes are going to be in the range of a few 1-3 um. The practical though is trying to teach you general techniques, not necessarily to know the length of chromosomes.