Check with your teacher before you properly listen to what I say, but I
think we don't need to know the 2nd law any more, because it relates more to the results using dihybrid crosses and in the new syllabus we only have to cover monohybrid crosses - I
think] .
But anyway, from what I understand it goes like this:
The first law says that each person has 2 factors for one characteristic (two genes for the one phenotype).
So I'll use the example of black hair. Say you have Hh, that means you have the dominant gene H - so you have the black hair, and also the recessive h - which just bums around and does nothing. So you have 2 genes for the one thing.
You also have freckles Ff. ( F being the dominant have freckes one, f being reccesive useless one).
Now if your cells are creating gametes (splitting up via meiosis to become sperm/eggs) then each of these cells has Hh, Ff and when they split, each will get one of the two hair genes, and one of the two freckle genes. But when they split, there is no way to tell which goes where -
each pair of factors sort out independantly of others.
So the 2 sex cells (actually 4 because of mitosis first, but meh)
could each end up with a h & f, a H & f, a h&F or a H&F, you don't know which H/h will pick which F/f
Essentially, it just says, that there is no way of telling what they'll do, they do it indepently - its not like they buddy up and both the dominants (H and F) will go off together. His experiment showed this because there was no obvious pattern of anything buddying up, it appeared random.
The problem with his 'law' (and also prolly why I
think they trashed it from the syllabus) is that for some genes there
is a pattern, but only some - mostly related ones, so if it was a gene for black hair and a gene for curly hair then they might buddy up when dominant.
Hope this helps
. I tend to ramble and use vague terms (like buddy) but hopefully we don't need to know any of it anyway.
