Genetics question

Hi
I found this exchange between two posters on a blog. I’m just calling them A and B for simplicity. I think both answers are flawed or incomplete. I’m trying to get a better answer. I look forward to your feedback.

A: Ok let me put it simply as this: 1 chromosome in your body is comprised of 2 chromatids (1 chromatid from your mom and 1 chromatid from your dad) Since you get one allele from each parent you therefore have 2 alleles for each gene on 1 chromosome.
B: I don’t think that’s accurate… 1 chromosome is made of 2 sister chromatids, but both of these chromatids are identical (hence why crossing over in Prophase I occurs between non-sister chromatids). I think wikipedia is right, we all have 1 copy of a gene and 2 alleles. There should only be one allele per chromosome. In this way, since we all have 2 chromosomes (one from dad, one from mom) per gene we should have 2 alleles per gene. The two alleles should be on separate homologous chromosomes…
I think B is correct and I actually made a flash card of it to help those that are more visual learners.

Both are wrong. “Sister chromatids” are what you call the two (half) new copies of chromosomes during the process of copying but before they separate. It is a moment in time. Look at the wiki.

I see that this is the thread. I find it disturbing that the official ADA practice test got the answer wrong.

Thanks Darren Garrison. My feeling was correct. I expected a higher standard from the ADA.

Good God, that was some serious misinformation on that page. At least dentists don’t have to know much about genetics to be able to fix your teeth.