Genetics question

Factual Questions
1

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.

2

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.

3

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

4

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

5

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.