Chromosome Fusion in Humans - or Not?

[Rumraket (Mikkel R.)]

@scd

so yes- evolution has no problem to explain gene loss, even at large scale.

… if the genes don’t positively contribute to reproductive fitness. Do the genes on the two fused chromosomes not contribute to reproductive fitness?

[scd]

@Rumraket

if the genes don’t positively contribute to reproductive fitness. Do the genes on the two fused chromosomes not contribute to reproductive fitness?

not if human lost them.

[Rumraket (Mikkel R.)]

@scd

not if human lost them.

I have no words.

[CrisprCAS9]

@scd

fruit fly and soil nematode have lost more than 1000 genes. elephant lost more than 1000 OR genes etc:

@scd

i know that horse has 64 chromosomes, mule has 63 and donkey 62 (although I have not checked yet if this is the result of chromosomal fusion, chromosomal loss etc).

It is a complex collection of rearrangements, as I understand it. Effectively no lost material.

@scd

so yes- evolution has no problem to explain gene loss, even at large scale.

Any example you give of generic gene loss is irrelevant to the point. It must be an example of the actual loss of a chromosomes genetic complement. Rearrangements resulting in chromosome number reduction is not a loss of genetic complement. Losing any number of unlinked genes is extremely different from losing an entire chromosome. Do you understand this?

[RonSewell (RonS)]

@scd

not if human lost them.

My o’ my. It is almost painful to have to point out a fact this obvious, but loss of scattered genes due to neutral mutation or relaxed selection is a very different affair from chromosome loss. Here are the genes which would be lost with a wholesale deletion of chromosome 2.

Wiki - Chromosome 2
Category:Genes on human chromosome 2, “0-C”
Category:Genes on human chromosome 2 “D-I”
Category:Genes on human chromosome 2 “I-P”
Category:Genes on human chromosome 2 “P-T”
Category:Genes on human chromosome 2 “T-Z”

[evograd (Blogging Graduate Student)]

The loss of 1000 genes gradually over hundreds of million of years (while others appear) is not comparable the loss of 1000 genes in a single generation. This isn’t conceptually difficult.

[scd]

@Rumraket

I have no words.

i was sarcastic. if human was still alive even with fewer chromosomes- it means that these genes were not so important.

@CrisprCAS9

Losing any number of unlinked genes is extremely different from losing an entire chromosome.

@RonSewell

loss of scattered genes due to neutral mutation or relaxed selection is a very different affair from chromosome loss.

@evograd

The loss of 1000 genes gradually over hundreds of million of years (while others appear) is not comparable the loss of 1000 genes in a single generation. This isn’t conceptually difficult.

some creatures (such as the flatworm schmidtea mediterranea) have lost almost half of their ancestral gene families. thus there is no real problem for evolution to explain a missing chromosome.

[evograd (Blogging Graduate Student)]

@scd

have lost almost half of their ancestral gene families. thus there is no real problem for evolution to explain a missing chromosome.

You quoted my comment directly above this reply. Try reading it again, slowly, and then respond with something relevant instead of repeating the same point that my comment was responding to.

[Michelle (Michelle Ols)]

@scd

i know that horse has 64 chromosomes, mule has 63 and donkey 62

Mules are the result of breeding a female horse with a male donkey. As a result of challenges with chromosomal pairing, mules are sterile (except on a few extremely rare occasions) because productive embryos cannot be made.

So this is an example of why chromosomal loss in higher organisms would be highly problematic. The mule example is not even an example of spontaneous chromosomal loss, but is a result of breeding across species.

[CrisprCAS9]

@scd

some creatures (such as the flatworm schmidtea mediterranea) have lost almost half of their ancestral gene families. thus there is no real problem for evolution to explain a missing chromosome.

The only way you could make this statement in response to the quotations in question is if you are completely unfamiliar with any of the science involved. Which is entirely consistent with every comment I’ve ever seen from you. You are wrong, the reasons have been explained repeatedly. Please go learn basic biology.

[scd]

@evograd

You quoted my comment directly above this reply. Try reading it again, slowly, and then respond with something relevant instead of repeating the same point that my comment was responding to.

do you agree with me that a creature can lose about half of its genes? (even in about 100 my). in addition, do you agree that even if it will lose about 10% of its genes in a single (or few) genetic event, its possible that that creature will be just fine?

@Michelle

So this is an example of why chromosomal loss in higher organisms would be highly problematic.

If the creature loses a chromosome and still lives- it will not be a problem in this case.

@CrisprCAS9

You are wrong,

if you say so.

[CrisprCAS9]

@scd

if the creature lost a chromosome and its still alive

Then provide an example that is actually relevant. Mules don’t lose the genetic complement of an entire chromosome, they have the same genes packaged differently and so they aren’t a relevant example. Gene loss in planarians and the other organisms you’ve referenced is neither linked nor simultaneous, so they aren’t relevant examples either. Provide a relevant example, or admit you are wrong.

[Michelle (Michelle Ols)]

@scd

If the creature loses a chromosome and still lives- it will not be a problem in this case.

It certainly is a problem. The donkey and the horse chromosomes are so different that the mule becomes infertile because it cannot produce viable embryos with mis-matched chromosomes, where large components of the chromosomes would be lost in the 3rd generation

[r_speir]

@Rumraket

Given that humans stand out from the rest by having fewer chromosomes, the most probable explanation is that humans must have somehow evolved fewer chromosomes after we split off from the most recent common ancestor shared with chimpanzees. One way this can happen is by chromosomal fusion. A chromosomal fusion is thus a prediction of common ancestry, and that is what we find.

You are getting “possession” of genetic material confused with “ownership” of genetic material. Chimps possess 24 pairs of chromosomes that God owns. In creating the Human Kind, God may have simply taken what he owned and fused chromosomes #2a and 2b. Chimps do not own that original genetic material as you would have us believe, such that we Humans must derive from chimps. This is how you go too far and force-fit the data to your narrative.

So do chimps and Humans have a common ancestor? Only in a genetic sense. We seem to have both derived from an original set of 24 chromosomes and some genetic engineering by our Creator. Still, both creatures enjoy the status of distinct created kinds.

[Faizal_Ali]

@scd

not if human lost them.

And we didn’t lose them.

You do know that.

Right?

[evograd (Blogging Graduate Student)]

@scd

do you agree with me that a creature can lose about half of its genes? (even in about 100 my). in addition, do you agree that even if it will lose about 10% of its genes in a single (or few) genetic event, its possible that that creature will be just fine?

Organisms can lose a lot of genes over millions of years, most notably in the course of evolving towards parasitic niches - these tend to be microorganisms. This is completely disconnected from the case of losing a chromosome in a single generation.

It’s possible a species could survive losing 10% of its genes over a much shorter timescale, if those genes were essentially cherry picked, but again this is disconnected from the loss of a whole chromosome - chromosomes contain an assortment of essential and accessory genes.

If humans can just dispense with entire chromosomes, I would expect there to be a few documented medical case reports of this happening. Do you have any such examples? Or would you propose that God could have initially created humans with useless chromosomes but these were lost and only now are all our chromosomes essential?

[colewd (Bill Cole)]

@evograd

Organisms can lose a lot of genes over millions of years, most notably in the course of evolving towards parasitic niches - these tend to be microorganisms. This is completely disconnected from the case of losing a chromosome in a single generation

What are your thoughts on how fairly rare events get fixed in a population through drift?

[Dan_Eastwood]

I’d like to comment that @thoughtful created a very good OP. Questions are clearly stated, previous comments quoted, and time stamps for the video. Very well done, and everyone should take note.

[Mercer (John Mercer)]

@scd

do you agree with me that a creature can lose about half of its genes?

No, a species might, but a creature never will.

@scd

(even in about 100 my).

Creatures do not live for 100 MY. AFAIK, species don’t either.

Have you considered that you may have a major conceptual issue in what appears to be your failure to grasp that evolution only happens to populations, never to individuals?

[Mercer (John Mercer)]

@r_speir

Chimps do not own that original genetic material as you would have us believe, such that we Humans must derive from chimps.

Straw man. No one is claiming that humans derive from chimps.

@r_speir

This is how you go too far and force-fit the data to your narrative.

You don’t even appear to have the most basic grasp of the narrative if you think it involves humans deriving from chimps.