Aneuploidy and polyploidy

[horsebox]

Is polyploidy when there are more than 2 homologous chromosomes while aneuploidy is when there are more or less than 23 pairs or is it the other way around? I read on one site the former but my lecture notes claim trisomy 21 is a case of aneuploidy. Which is it?

 

[Hercules Rockefeller]

Is polyploidy when there are more than 2 homologous chromosomes

Yes.

Polyploidy is any case other than haploidy and diploidy. ie. polyploid = more than 2 homologous copies of each chromosome, as opposed to diploid = 2 homologous copies of each chromosome, and haploid = 1 copy of each chromosome.

while aneuploidy is when there are more or less than 23 pairs….

Yes. (Although your example is specific to humans.)

I think aneuploidy is an abnormal number of chromosome copies for that organism.

So, for instance, cotton plants are polyploid (tetraploid) organisms. But if you disrupted the meiotic spindle with the chemical colchicine (resulting in the inheritance of extra sets of chromosomes) you would create aneuploid cotton plants (maybe hexaploid).

Taking humans as an example (normally diploid with 23 pairs of homologous chromosomes), a defect in meiosis might lead to an aneuploid embryo with an extra copy of the maternal chromosomes resulting in 46+23 = 69 chromosomes. (I doubt the embryo would be viable.)

I read on one site the former but my lecture notes claim trisomy 21 is a case of aneuploidy. Which is it?

Trisomy 21 would be a case of aneuploidy with respect to chromosome 21, not with respect to the whole genome.

 

[horsebox]

So aneuploidy just refers to ANY abnormality in chromosome numbers then? I suppose this kinda thing only really happens with abnormal numbers of copies of chromosomes because theres no meiotic mistakes that are gonna result in 46 chromosomes then 2 completely new unique chromosomes on top of the 46.