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re: Why hybridize?
Well, lets start with DNA.
DNA analysis involves techniques like PCR, RFLPs and sequencing to
name just 3. All involve taking a small (v.small) piece of DNA and
comparing it or its components to that of another equally small
sample. The ends of chromosomes (the telomers) are normally used as
they will statisticly yield an unique pattern which can be compared
between INDIVIDUALS. There can be as much variation between
individuals as between species. This is then pretty useless unless
you go and examine specific genes using PCR or RFLPs. (Sequencing is
too tedious and expensive).
I believe there is also a method in which people join samples of DNA of two
individuals, to see how much they react/interact. In this way they can see how
much different species are related or if they are different species at all.
THe idea is that if they are distinct species 2 things may happen in
the first (F1) generation: 1) the offspring will look nothing like
either parent; & 2) the offspring will be sterile.
Naturally, if they are not sterile it will mean the first round will
belong to the "1-specie-hypothesis". But one battle does not win the
war, for if they are one specie then it stands to reason that the
different colour pattern is the result of some or other mutation
which was selected naturally over time, and by breeding subsequent
generations from the F1 the original strains will resurface in some
or other genetic pattern (Mendelian or some thing else).
This is not entirely true,
When you have a plant that has homozygote dominant genes for red flowers and
cross that one with a plant that has homozygote recessive genes for white
coloured flowersyou get the following crossing:
RR x rr this will render you 100% Rr that areall plants with red flowers in
Rr x Rr will render you 25 % RR , 50% Rr and 25%rr in the F2 (75 % red and 25
So when you look at just one gene it is true you can get the original strain
back in the F2, but all organisms have thousands of genes, so let's look what
happens when we are looking at two genes.
We take the example above and a gene that gives shape to leaves let's say
round (S, dominant) and pointed (s, recessive)
SS x ss will render you 100% Ss in the F1 (round)
Ss x Ss will render you 25% SS 50% Ss and 25%ss (75% round and 25% pointed) in
The chance on F2 that are identical to one of the parents is now 12,5 %, that
was 25% when you just look at one gene
When you start considering all genes the chance on a genetically equal
individual to one of the parents is practically 0%.
And this is a very simple model, because you have dependant and independant
genes, X-chromosomal inheritance, crossing-over and all kinds off mutations
that are diminishing your chance on an individual that is exactly the same as
one of the original parents.
Like I said before, when a scientist desperately needs a
crossbreedingexperiment to determine the species, that's fair enough. I will
not allways agree, but o.k. I do think however that hobbyists should not do
these things at all, we mostly know too little about genetics to produce
usefull data, and when you do know enough you are or should become a
scientist, because otherwise your data will probably not be scientifically
recognised. When a hobbyist is crossbreeding fish for himself it will be makin
fun over our fishes backs. Like someone said, it would be like crossing humans
with Bonobos just for fun, and I don't think we want to do that, don't we?
Hartelijke groeten van Jochem 't Hoen
jochem.thoen at 98_student.wau.nl
jochem at fgbbs_iaf.nl
no guts, no glory!
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