 Aneuploidy happens when you have an odd number of chromosomes, an abnormal number of chromosomes in your karyotype. Your cells end up with an abnormal number of chromosomes. Now, most cases of aneuploidy, most cases of too many chromosomes or not enough chromosomes result in death. This is miscarriage when when if you make a kid that has the wrong number of chromosomes, you might not even know that you made a kid because that it's not going to survive. There are a few examples of aneuploidy that are survivable and the the malfunction happens in meiosis. There's a process in my that moment of separating chromosomes either in meiosis one or meiosis two when anaphase happens. In anaphase one we had homologous chromosomes separate, non-disjunction is this process of failure to separate. So if those sisters or homologs say nice try this is my homey this is my homey log I'm not leaving that guy that's non-disjunction follow it through if non-disjunction occurs in meiosis one look what happens one of our resulting cells is missing an entire chromosome and the other one has two copies where there should just be one. So it ends up with two half of the gametes have one too few chromosomes and half the gametes have one too many from this one event this one non-disjunction event non-disjunction can happen between sisters and so it can happen here in my meiosis two and it's the same thing it's non-disjunction only this time we end up with half the chromosomes are normal or half the gametes have the normal number of chromosomes and only half of them one of them has one too many and one of them has one too few because the non-disjunction event happened later in meiosis after we had one normal division take place non-disjunction um you end up with the full chromosome extra in the gamete and then imagine if any of those gametes meet up with a another gamete that has the normal number you're gonna end up with one too many or one too few how do you know and why genetic testing is one of the things that they're looking for is when they do genetic testing on a pregnant human they'll look at the they'll do a karyotype and they'll be like dude let's count and see what happens you push pause go ahead and push pause and then see if you can find the place or the the aneuploidy event in this karyotype right here so you push pause I almost pushed pause because I was following my own directions super important to follow directions but I'm assuming that you're back now did you do the job did you go and find the issue well sometimes these karyotypes are interesting to peel apart or to look at but you can sort of go through and go okay yeah I see my pairs I see my homologous pairs and I see how like the staining of them I could if I were given a big pile of these chromosomes I could actually sort them out into groups and I can see everything and it looks like am I right that there are two of everything I see two of everything some things are like kind of bent and weird but I still can look at it and be like okay I see the banding the dark and the light lines like that they still look the same they just look bent yeah yeah yeah I feel good I'm assuming that there's one chromosome here so I'm like this is at the end of our giddy up I probably should count except that I know that that's the X chromosome this should be the 22nd chromosome and this should be the 21st chromosome right we could probably count back you could push pause and count back and make sure I'm correct we have one X chromosome what's that that's the Y chromosome except what's true there are two Y chromosomes that's an example of aneuploidy we shouldn't have two Y chromosomes now interesting that's an example of an aneuploidy you may never know about an extra Y chromosome doesn't have a huge impact an extra X chromosome will one X chromosome and know why chromosomes will you will see but it you survive that's something you can survive probably the most common aneuploidy is trisomy 21 do you know what that is that's the condition that that's the non-disjunction event that results in Down syndrome and one extra chromosome 21 is totally survivable and you just have a little extra DNA and and you have Down syndrome okay how do we feel about where we going next next up we're going to talk about pedigrees and pedigrees are a strategy for analyzing human inheritance patterns when we can't like go around making babies in vials and dumping them into counting chambers yeah we're not going to do that with humans so let's talk about pedigree