populations of organisms

[kitty82]

Can anyone explain how the number and the size of populations are affected by genes, alleles and heterozygote to the next generation? And what exaclty is genetic drift? This made me really confused. Thanks.

[MrMistery]

Research speciation. Since members of a population are all part of the same species.

Genetic drift.. Hmm.. i don't know the deffinition.. here's one off google..
- random change in allele frequencies through the generations owing to chance events alone". Especially in small populations, the ideal of the Hardy-Weinberg rule is violated. By chance the individuals carrying one allele may either die more than expected or reproduce less than expected, leading to a loss of that allele in the next generation.

[swatkat]

i think mr mistery's material will help
genetic drift usually results in a larger number of homozygotes and very less heterozygotes
it may even lead to speciation

[baikuza]

pick this words.

scientists believe this evidence is caused by the density-dependent... i hope i spell it correctly.

you know in microscale experiment such as tissue culture, the cells stop to growth and doing reproduction if the medium if full. i mean the surface of the medium is full of them. so that both plasma membranes are touching each other. automatically.

this is the same at ecosystem the larger scale...

[AstusAleator]

???
I didn't understand that Baikuza.

Genentic drift is random, and thus density independent. For example: Say you have a population of 25 homozygous dominants (HD), 50 heterozygotes (He), and 25 homozygous recessives (HR).
Now lets say that the population is mixed over an area. At any time, in any section, you may find more HDs or more HRs. Or you may find equal portions. Genetic drift occurs when a segment of the population containing undequal proportions of dominant to recessive is removed permanently.
So say the segment that is removed contains 15 HDs 20 Hes and 5 HRs. The resulting population is 10:30:20. There has been a net loss of dominant genes relative to the population. The genotype of the population is now more characterized by the recessive than the dominant, where they were in balance before.
Or take a more extreme example and say that all of the HDs and Hes were eliminated. The resulting population is entirely HR.

Just remember that it relies on stochastic (random) events.

[baikuza]

@AstusAleator

you are talking the right too. it refers to the genes...
but what I'm talking is about "how the number and the size of populations are affected by genes". as you know denstiy-dependence(the correct spell) may also controled by genes. you get it know?
at several condition like cancer cell, which has a different protein/ activities-protein related to genes, DNA too.
they not serve the density-dependence...as the result of the changed metabolism...(the gene(s) i think)

so we are correct to say what we have said.
(^^)