Translocation

00:00 Let’s go on to look at a condition of translocation. When we translocate between two chromosomes, there’s going to be some issues of how those chromosomes line up during cell division, specifically in the formation of the gametes on what gametes could be formed by those. In order for chromosomes to pair as homologs, they actually have to form this quadrivalent formation. That can form either balanced or unbalanced gametes. When the gametes are unbalanced, we’re going to see that the gametes end up producing some chromosomal abnormalities that could have features.

00:46 Now, we moved on from cri-du-chat, totally different situation here with translocations from one chromosome to another. Multiple disorders could end up from these translocations. So, the first situation here is if they form the quadrivalent, they can only form it really in one way. If those chromosomes split on the horizontal axis, then we end up with unbalanced gametes. Unbalanced gametes, again you’re going to have some repercussions that would show up in the conceptus that results.

01:24 If they split on the vertical axis, those homologs that are arranged in quadrivalent formation split on the vertical axis, we also would have unbalanced gametes developed from that.

01:40 Now, there’s one condition in which we could end up with the translocation in formation of balanced gametes.

01:49 So, we form the quadrivalent but now between the divisions, we see that the two pieces go on the diagonal. So those two pieces will end up in one gamete. The other two pieces will end up in another gamete. Thus, we form actually one normal and one balanced gamete.

02:12 So, each of those situations have all the right amount of genetic information. So, we’re in that just right zone.

02:21 But with the balanced situation, we could end up with a little bit of a repercussion. Balanced translocations result, here is a reciprocal translocation. Again, we have translocated and the balanced translocation, formation of gametes results in about 1 in 2000 newborns. If it’s balanced genetically, usually, we’ll have no particular phenotypic disturbance. However, sometimes you’ll see that specifically where the translocation occurred disrupted a gene. On occasion, you may see some repercussions because of precisely where the split happened, although they have a complete complement of genetic information. Now, these balanced translocations though might end up forming unbalanced gametes in the F2 generation. So, the individual with the balanced translocation is just fine but its offspring would likely have or result from unbalanced gametes because the F1 gametes would end up being unbalanced. Thus, these gametes end up being fertilized by a sperm or egg whichever way that comes around and end up with a genomic imbalance in the F2 generation, which could be fatal or it could persist either way.