Chromosomes and Karyotypes

We make pinned comments for clarifications or corrections. Some updated versions of textbooks are using a more detailed definition of molecular sequences making up the centromere - which means that when you have a chromosome with replicated chromatids - you could consider it to have two centromeres (one per sister chromatid) although they are bound together in a region. Many textbooks still refer to a single centromere on a chromosome with two fully attached sister chromatids - as they are considering the complex where the centromeres are attached - and then they show fully separated sister chromatids with their own centromere. While we have done this as well by illustrating one centromere per eukaryotic chromosome, we think it is important to understand this complex is where they are joined with cohesin in the case of sister chromatids - as well as also understanding how the definition of centromere has changed. You can see a conversation about this here: twitter.com/AmoebaSisters/status/11926218686054195… It would have been better for us to have said "centromere region" - and again, when sister chromatids are attached at the centromere region, it is still counted as one chromosome. If we update this video, we'll probably feature this information about the centromere and we'd like to improve our drawing to show the bound centromeres. -------- Other things to note: just as we mention in our video about Punnett squares with sex-linked traits, we want to add this here too: there is more detail to sex determination than just sex chromosomes and more combinations possible than XX and XY combinations. We have some further reading links you can check out linked in the other video and we also want to paste in some of the examples from that description here: XXY: www.genome.gov/Genetic-Disorders/Klinefelter-Syndr… XYY: medlineplus.gov/genetics/condition/47xyy-syndrome/ X: www.genome.gov/Genetic-Disorders/Turner-Syndrome Info about SRY gene & also conditions related to variants in SRY gene: medlineplus.gov/genetics/gene/sry/ -------- We appreciate the comment that there was a point in the video where one of our chromosomes had sister chromatids that didn't match in our illustration! It has been corrected. (Sister chromatids should be identical) -------- This is not our only playlist about chromosomes- we have a heredity playlist here! youtube.com/playlist?list=PLwL0Myd7Dk1FVxYPO_bVbk8… Also, you can find resources that go with our videos here www.amoebasisters.com/handouts

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Thank you SOOO much for this!!! I have literally spend my entire life trying to figure out why two sister chromatids are still a chromosome, and you explained it so simply. These videos are the best!

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