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Ben99

Considering two different species of yeasts having the same genome, do they have also the same number of chromosomes and genes?

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Hello there, 

I have this question that I can not surely answer. For me the Answer is no but I am not sure and I can not motivate. Can Someone help me trying to motive the answer? Thank you 

Kind regards

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If they have the same (identical) genome then surely they are the same species?

Also, I would assume that "genome" includes the division into chromosomes, so that would also be the same. And if the genome is identical then the genes must be identical.

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The point is that the question is based on the concept that 2 species of yeasts are different but they have the same genome. How can I motivate if they have or not have the same number of chromosomes or genes?

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55 minutes ago, Ben99 said:

The point is that the question is based on the concept that 2 species of yeasts are different but they have the same genome.

Is that possible?

(I suppose they could have been wrongly classified as different species, but then the genetic analysis shows they are actually the same.)

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If there genomes are the same, then their chromosomes and genes must be the same. It is important to note that within a species there can be many variations between the actual sequences. If you would have an exact copy of the genome, you would have an exact copy of that species. Do note that two identical genomes can have different phenotypes, based on environmental/epigenetic stimuli  and because of inherent stochastic behaviour. I think, but I am not sure, that variation within organisms with identical genomes and cultured (or naturally growing in) in similar environments will be approximately normally distributed. 

As Strange mentioned, if you find identical genomes, it may be that the two 'species' are actually just one and were misclassified. 

One motivation for why identical genomes should have identical gene number and chromosomes is that each chromosome has some DNA regions which help with the overal form/structure of the chromosome (and are important in replication). These regions are called the centromere and  telomeres. Having a chromosome less would mean that when we compare the total genomic sequences, there should be 1 centrosome and two telomere regions missing. Since these are DNA sequences, their genomes CANNOT be the same. 

Of course, within identical species there will be natural variation of telomere size, but I think that if we would consider every variation, then there would never be an 'identical' genome, so I guess it depends a bit on how strict you are with using 'identical'.

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1 hour ago, Strange said:

Is that possible?

(I suppose they could have been wrongly classified as different species, but then the genetic analysis shows they are actually the same.)

This question was asked in a test I found. They start from the fact that those 2 species of yeast have the same genome ( so It is something not debatable) and from that I have to say if they have or not the same number of genes and chromosomes, also motivate the Answer. The problem is that I do not know how to respond cause I think the question is a bit trick

 

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3 minutes ago, Ben99 said:

This question was asked in a test I found. They start from the fact that those 2 species of yeast have the same genome ( so It is something not debatable) and from that I have to say if they have or not the same number of genes and chromosomes, also motivate the Answer. The problem is that I do not know how to respond cause I think the question is a bit trick

It is a bizarre question, but the answer is that they must have the same number of chromosomes and genes if they have the same genome.

It's as if someone asked: "if the contents of these two books are the same, do they have the same words and chapters?"

The answer is: Yes, because that is what the "have the same contents" means.

(Maybe the people who wrote the question don't actually know what the words "genome", "chromosome", etc mean.)

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I agree, it's a poorly conceived question, unless there really are two populations of yeast with identical loci & associated alleles, but loci & chromosome numbers  arranged differently. Then it would be a matter illustrating the difficulty of defining "species." 

If the two populations indeed had all the same loci & alleles, then they would be phenotypically/biochemically the same, although with differing chromosome numbers, they couldn't interbreed without producing some confusing polyploidy. edited to add: Reproductive isolation is the first step on the road to speciation.

OTOH- as one who sees the veracity of The Gaia Hypothesis, to me, it doesn't make any difference one way or the other :-)

Edited by guidoLamoto

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no https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3141009/

Quote

the number of chromosomes in post-WGD species now ranges between 10 and 16 and the number in non-WGD species (Zygosaccharomyces, Kluyveromyces, Lachancea, and Ashbya) ranges between 6 and 8

 wiki:

Quote

In the fields of molecular biology and genetics, a genome is the genetic material of an organism

genome (ancestary) > species (divergence)

https://en.wikipedia.org/wiki/Genetic_divergence

it's seemingly a "trick" evolution question ?

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On 2/17/2020 at 5:47 PM, guidoLamoto said:

I agree, it's a poorly conceived question, unless there really are two populations of yeast with identical loci & associated alleles, but loci & chromosome numbers  arranged differently. Then it would be a matter illustrating the difficulty of defining "species." 

If the two populations indeed had all the same loci & alleles, then they would be phenotypically/biochemically the same, although with differing chromosome numbers, they couldn't interbreed without producing some confusing polyploidy. edited to add: Reproductive isolation is the first step on the road to speciation.

OTOH- as one who sees the veracity of The Gaia Hypothesis, to me, it doesn't make any difference one way or the other :-)

How can you have the same DNA, and have differing numbers of chromosomes? Centromeres are DNA, telomeres have DNA portions right? But even disregarding those two regions, spatial proximity within in the 3D genome regulates (some part of) gene transcription etc. With more/less chromosomes, their proximity may not be the same, therefore there is no reason to believe (in my opinion) they would be phenotypically the same when they contain all the genomic/epigenetic, seperated into a different number of chromosomes (ignoring the chromosome-specific DNA regions). Replication is by definition a different process when there are more chromosomes present. As cells are dynamic systems, small changes in starting conditions may lead to significantly different outcomes.
 

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On 2/19/2020 at 7:58 PM, Dagl1 said:

How can you have the same DNA, and have differing numbers of chromosomes? Centromeres are DNA, telomeres have DNA portions right? But even disregarding those two regions, spatial proximity within in the 3D genome regulates (some part of) gene transcription etc. With more/less chromosomes, their proximity may not be the same, therefore there is no reason to believe (in my opinion) they would be phenotypically the same when they contain all the genomic/epigenetic, seperated into a different number of chromosomes (ignoring the chromosome-specific DNA regions). Replication is by definition a different process when there are more chromosomes present. As cells are dynamic systems, small changes in starting conditions may lead to significantly different outcomes.
 

 

When I first glanced through this thread I scoffed. Misunderstanding about the meaning of genome. But I've been thinking about ploidy and wondering if my response is more about the genomes and chromosome systems that I am most familiar with.

From Wiki on ploidy:

Many animals are uniformly diploid, though polyploidy is common in invertebrates, reptiles, and amphibians. In some species, ploidy varies between individuals of the same species (as in the social insects), and in others entire tissues and organ systems may be polyploid despite the rest of the body being diploid (as in the mammalian liver). For many organisms, especially plants and fungi, changes in ploidy level between generations are major drivers of speciation.

Does this put some reality back in the OP?

Thanks in advance.

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3 minutes ago, druS said:

 

When I first glanced through this thread I scoffed. Misunderstanding about the meaning of genome. But I've been thinking about ploidy and wondering if my response is more about the genomes and chromosome systems that I am most familiar with.

From Wiki on ploidy:

Many animals are uniformly diploid, though polyploidy is common in invertebrates, reptiles, and amphibians. In some species, ploidy varies between individuals of the same species (as in the social insects), and in others entire tissues and organ systems may be polyploid despite the rest of the body being diploid (as in the mammalian liver). For many organisms, especially plants and fungi, changes in ploidy level between generations are major drivers of speciation.

Does this put some reality back in the OP?

Thanks in advance.

Could you elaborate, I am not getting entirely getting the question, although I will repeat what I said before in a little more detail: the genome contains structural parts of chromosomes, such as telomeres and centromeres. These are DNA regions that don't encode for proteins (and we generally don't really think of them when discussing the genome), but they are part of the genome. If one would have additional chromosomes/telomeres, then they do not have the same genome.

Of course, if what was meant was; similar genomes, then of course that is possible. But as the question was about the same (identical) genome, it must also mean they have the same amount of chromosomes. 

Did I answer the question or completely miss the ball? 

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4 minutes ago, Dagl1 said:

Could you elaborate, I am not getting entirely getting the question, although I will repeat what I said before in a little more detail: the genome contains structural parts of chromosomes, such as telomeres and centromeres. These are DNA regions that don't encode for proteins (and we generally don't really think of them when discussing the genome), but they are part of the genome. If one would have additional chromosomes/telomeres, then they do not have the same genome.

Of course, if what was meant was; similar genomes, then of course that is possible. But as the question was about the same (identical) genome, it must also mean they have the same amount of chromosomes. 

Did I answer the question or completely miss the ball? 

Dagl1, you seem to be reacting in a manner that suggests I am being aggressive against your input? Sorry mate if you think that, but it's not the case.

Can I be offered a genuine interest?

I would have completely stood by your statement over genomes. Certainly within my understanding of diploid organisms. I put out a query based on ignorance and interest. Let's focus on one single statement from wiki that I quoted In some species, ploidy varies between individuals of the same species.

How does this effect genome? Genuine question, no challenge here.

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12 minutes ago, druS said:

Dagl1, you seem to be reacting in a manner that suggests I am being aggressive against your input? Sorry mate if you think that, but it's not the case.

🤫 It seems aggressive?? Not my intention, could you also elaborate on what makes it sound aggressive so I can change that for the future?

I did offer you my genuine interest, but also see I missed the ball on your question.

Changes in ploidy (ploism?) will probably not have much effect (do not read 'no changes') depending on the species (in the case of social animals which change sex, based on the environment, this may well be one reason for phenotypical changes), but I don't see any reason why it would have to cause changes (if all else remains equal, and each gene region still can come into contact with the right parts of the DNA and everything remains accessible), although as the quote mentions it may be the start of speciation. I am not familiar enough with the actualities, but to come back to the topic at hand, these individuals within the species will not have the same genome at that point. 

I do get that I may be looking at this too stringently, as we can of course say that broadly speaking humans have the same genome, but if we would be looking at the exact sequences, we won't find any human with identical DNA. I suppose that way of looking at things isn't very functional, but I do stand by my answer to OP.

-Dagl

 

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Love it Dagl1 - your response tells me I must keep studying! [But also gives me some specifics I want to test as I go forward.]

(FWIW I would have thought identical DNA means a clone, I dont think that was the intent of the OP.)

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On 3/23/2020 at 5:36 AM, druS said:

(FWIW I would have thought identical DNA means a clone, I dont think that was the intent of the OP.)

Perhaps not, but ultimately an identical genome means that something is effectively a clone. 

 

On 3/23/2020 at 5:17 AM, Dagl1 said:

I do get that I may be looking at this too stringently, as we can of course say that broadly speaking humans have the same genome

Not to stringently in common use, each human (aside from identical twins, though even there one might find differences) carries its own genome. There is large similarity but broadly speaking we do have similarities to various degrees with all organisms on Earth.

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