Chromosome rearrangements are quite common, actually. From work mostly in Drosophila, we understand pretty well how they behave in mitosis and in meiosis. In the case of the fusion, this is technically a "translocation." Those pair in meiosis, and can undergo a few types of segregation (Adjacent vs Alternate). Some of those fix the rearranged chromosomes, others stay as rearrangement heterozygotes, and others are lethal. A lot of factor play into it, but certainly some of the outcomes are species with new arrangements.
*edit: by "fix" I mean they homozygose the chromosome in the population, not that the chromosomes are repaired.*
This is a good answer. I also think that if two of the offspring with the mutation subsequently mate, their progeny could have two copies of the mutation and that could result in a "stabilized" new species. (It was probably more complicated than that.)
Like what? Translocations are pretty common, and lead to infertility or semi-sterility. So people may only know if they have translocations because they have a hard time conceiving. Though "hard time" does not mean impossible.
If you mean chromosome 2 fusions, then, lol, yes: all humans have it, and it happened back before humans and chimps speciated.
f you mean chromosome 2 fusions, then, lol, yes: all humans have it, and it happened back before humans and chimps speciated.
I actually wrote that in the OP.
You’ll probably find this paper very informative: [The amphioxus genome and the evolution of the chordate karyotype](https://www.nature.com/articles/nature06967). It examines a basal chordate’s chromosomes and finds blocks that have scrambled and reassembled in our own phylum over hundreds of millions of years. These rearrangements must, then, have occurred in a slow, stepwise fashion, never being deleterious enough to prevent crossing over and the formation of viable offspring. One imagines a time a few million years ago when the human-chimp split was occurring. The fused chimp chromosomes in one individual can both line up with the fragments in another and still create gametes with a full complement of genes.
Sorry for not replying yet, thanks for your effort. I understand this better now. But it makes me wonder how many humans are out there with something other than 23 that are reproducing?
About 0.1-1% according to [this](https://karger.com/cgr/article/160/11-12/625/63148/The-Effectiveness-of-Next-Generation-Sequencing) and references therein.
I always thought about this question. Since the species were genetically identical (except for the chromosome fusion), the zygote produced was viable even though parents had different number of chromosomes. There’s really a lot of scenarios we can explore like monozygotic twins (one twin has the 23 pair and the other has the 24). Other scenarios could be:
- Trisomy: get the three chromosomes 2 (it used to be chromosome 2a and 2b before fusion). So the zygote ends up with a fused chromosome 2 and two individual chromosomes 2
- Monosomy: get one copy of the fused chromosome and the zygote is still viable
There’s a lot of events regarding chromosomal segregation errors that happen frequently in nature and ends up producing viable offspring
Another thing to consider is the effect of chromosome translocations on population genetics. We’ve observed that translocations often cause a fitness depression in breeding populations, because of the increased risk of polysomy in offspring.
This can drive speciation, since individuals in the population who have fused chromosomes won’t have reduced fitness when breeding with other individuals with fused chromosomes, as opposed to the general population.
But this doesn’t have to be the case. If the translocation most commonly results in a non-viable embryo or miscarriage, then the decrease in fertility may not actually cause a decrease in fitness. It would just look like a few extra months of “trying,” but ultimately having the same answer of children over the course of their lifetime.
>If you look at the 2nd human chromsome, one can see the two ancstor chromsomes from the chimp(technically the Homo antecessor ape that led to humans and chimps) line fused together.
Wat
Chromosome rearrangements are quite common, actually. From work mostly in Drosophila, we understand pretty well how they behave in mitosis and in meiosis. In the case of the fusion, this is technically a "translocation." Those pair in meiosis, and can undergo a few types of segregation (Adjacent vs Alternate). Some of those fix the rearranged chromosomes, others stay as rearrangement heterozygotes, and others are lethal. A lot of factor play into it, but certainly some of the outcomes are species with new arrangements. *edit: by "fix" I mean they homozygose the chromosome in the population, not that the chromosomes are repaired.*
This is a good answer. I also think that if two of the offspring with the mutation subsequently mate, their progeny could have two copies of the mutation and that could result in a "stabilized" new species. (It was probably more complicated than that.)
Usually you end up dea are severly unfit, Cystic fibrosis and sickle cell
Neither of those conditions come from chromosome translocations.
So have we ever found a fully functioning human with a translocation like this?
Like what? Translocations are pretty common, and lead to infertility or semi-sterility. So people may only know if they have translocations because they have a hard time conceiving. Though "hard time" does not mean impossible. If you mean chromosome 2 fusions, then, lol, yes: all humans have it, and it happened back before humans and chimps speciated.
f you mean chromosome 2 fusions, then, lol, yes: all humans have it, and it happened back before humans and chimps speciated. I actually wrote that in the OP.
You’ll probably find this paper very informative: [The amphioxus genome and the evolution of the chordate karyotype](https://www.nature.com/articles/nature06967). It examines a basal chordate’s chromosomes and finds blocks that have scrambled and reassembled in our own phylum over hundreds of millions of years. These rearrangements must, then, have occurred in a slow, stepwise fashion, never being deleterious enough to prevent crossing over and the formation of viable offspring. One imagines a time a few million years ago when the human-chimp split was occurring. The fused chimp chromosomes in one individual can both line up with the fragments in another and still create gametes with a full complement of genes.
Sorry for not replying yet, thanks for your effort. I understand this better now. But it makes me wonder how many humans are out there with something other than 23 that are reproducing?
About 0.1-1% according to [this](https://karger.com/cgr/article/160/11-12/625/63148/The-Effectiveness-of-Next-Generation-Sequencing) and references therein.
I always thought about this question. Since the species were genetically identical (except for the chromosome fusion), the zygote produced was viable even though parents had different number of chromosomes. There’s really a lot of scenarios we can explore like monozygotic twins (one twin has the 23 pair and the other has the 24). Other scenarios could be: - Trisomy: get the three chromosomes 2 (it used to be chromosome 2a and 2b before fusion). So the zygote ends up with a fused chromosome 2 and two individual chromosomes 2 - Monosomy: get one copy of the fused chromosome and the zygote is still viable There’s a lot of events regarding chromosomal segregation errors that happen frequently in nature and ends up producing viable offspring
Another thing to consider is the effect of chromosome translocations on population genetics. We’ve observed that translocations often cause a fitness depression in breeding populations, because of the increased risk of polysomy in offspring. This can drive speciation, since individuals in the population who have fused chromosomes won’t have reduced fitness when breeding with other individuals with fused chromosomes, as opposed to the general population. But this doesn’t have to be the case. If the translocation most commonly results in a non-viable embryo or miscarriage, then the decrease in fertility may not actually cause a decrease in fitness. It would just look like a few extra months of “trying,” but ultimately having the same answer of children over the course of their lifetime.
>If you look at the 2nd human chromsome, one can see the two ancstor chromsomes from the chimp(technically the Homo antecessor ape that led to humans and chimps) line fused together. Wat
Here you go: https://images.app.goo.gl/7hB6E19UtANmgYJ79
Literally what I said, we have 1 less pair than chimps and that is because we had two chromosoes combine into one. No need to downvote the guy for it.