If humans are 99.9% identical, how are we so different ? -If you know, please help

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Leah.J
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This question has been confusing me for the longest time, but I never really made an effort to understand, so here I am.

I don't understand how I can be 99.9% identical to a friend when every physical feature between us is different. I have curly hair she has straight hair, I am 5'9 she is 5'5, I have brown eyes , she has hazel, I have smaller bones and less muscle and she has wider bones and a lot of muscle... how is our genetic data so similar ?
The DNA that we both have exact copies of, what does it code for ?

And I recently learnt that a polymorphic gene is a gene which has more than one allele in the population.. doesn't this mean that the 0.1% of genes that make us unique are all polymorphic ?
The gene that codes for eye colour is polymorphic , true ?

Is an example of the gene that is not polymorphic the gene that codes for RNA polymerase ?
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Jpw1097
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(Original post by Leah.J)
This question has been confusing me for the longest time, but I never really made an effort to understand, so here I am.

I don't understand how I can be 99.9% identical to a friend when every physical feature between us is different. I have curly hair she has straight hair, I am 5'9 she is 5'5, I have brown eyes , she has hazel, I have smaller bones and less muscle and she has wider bones and a lot of muscle... how is our genetic data so similar ?
The DNA that we both have exact copies of, what does it code for ?

And I recently learnt that a polymorphic gene is a gene which has more than one allele in the population.. doesn't this mean that the 0.1% of genes that make us unique are all polymorphic ?
The gene that codes for eye colour is polymorphic , true ?

Is an example of the gene that is not polymorphic the gene that codes for RNA polymerase ?
First, not all DNA codes for proteins. A large proportion of DNA is non-coding DNA. Even within genes (regions of DNA that code for proteins) there are regions which do not code for proteins - these regions are known as introns.
Also bear in mind there are lots of genes that will be identical for people, for example, the gene that codes for haemoglobin, collagen, albumin or many enzymes will be the same between most people. Therefore probably only a relatively small proportion of genes will have different alleles.
Also, many polymorphisms/alleles differ by only a single base substitution, and therefore most of the DNA within the alleles will be identical.
Even if two humans’ DNA were 100% identical (such as identical twins), they still do not look 100% identical. This is because of epigenetics - environmental factors can alter the expression of different genes (i.e. switch on/off genes).

As you can see, not all regions of DNA even code for proteins, most genes that do code for proteins will be similar/identical between people, even in those genes that may vary between people (alleles), only small differences in DNA can lead to large changes in the protein. Even if DNA was 100% identical, the environment would alter the expression of genes, leading to differences in characteristics. Therefore only small changes in DNA are required to produce large changes in characteristics.
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Anonymous1502
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(Original post by Jpw1097)
First, not all DNA codes for proteins. A large proportion of DNA is non-coding DNA. Even within genes (regions of DNA that code for proteins) there are regions which do not code for proteins - these regions are known as introns.
Also bear in mind there are lots of genes that will be identical for people, for example, the gene that codes for haemoglobin, collagen, albumin or many enzymes will be the same between most people. Therefore probably only a relatively small proportion of genes will have different alleles.
Also, many polymorphisms/alleles differ by only a single base substitution, and therefore most of the DNA within the alleles will be identical.
Even if two humans’ DNA were 100% identical (such as identical twins), they still do not look 100% identical. This is because of epigenetics - environmental factors can alter the expression of different genes (i.e. switch on/off genes).

As you can see, not all regions of DNA even code for proteins, most genes that do code for proteins will be similar/identical between people, even in those genes that may vary between people (alleles), only small differences in DNA can lead to large changes in the protein. Even if DNA was 100% identical, the environment would alter the expression of genes, leading to differences in characteristics. Therefore only small changes in DNA are required to produce large changes in characteristics.
Can you please explain epigenetic a bit more? For twins they usually occupy the same environment so how does epigenetic come into play? Also what parts of the environment exactly effect epigenetics?
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ZombieTheWolf
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Epigenetics.
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Jpw1097
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(Original post by Anonymous1502)
Can you please explain epigenetic a bit more? For twins they usually occupy the same environment so how does epigenetic come into play? Also what parts of the environment exactly effect epigenetics?
Environment refers to more than just the geographical sense. These environmental factors include diet, exercise, smoking, alcohol, stress, environmental differences, illnesses, etc.

Of course, some differences between twins may be due to genetic differences - mutations.
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Hellohsjakodsmka
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E:oink:enetics
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Anonymous1502
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(Original post by Jpw1097)
Environment refers to more than just the geographical sense. These environmental factors include diet, exercise, smoking, alcohol, stress, environmental differences, illnesses, etc.

Of course, some differences between twins may be due to genetic differences - mutations.
Thank you for the further explanation. It is strange how some identical twins look more similar than others and then you get identical twins who look incredibly similar at a young age but as they become adults they look a lot more different.
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Jpw1097
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(Original post by Anonymous1502)
Thank you for the further explanation. It is strange how some identical twins look more similar than others and then you get identical twins who look incredibly similar at a young age but as they become adults they look a lot more different.
Exactly, as they get older the acquire more mutations (genetic differences) and epigenetic changes (due to environmental factors) which causes differences in their characteristics.
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Anonymous1502
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(Original post by Jpw1097)
Exactly, as they get older the acquire more mutations (genetic differences) and epigenetic changes (due to environmental factors) which causes differences in their characteristics.
You seem incredibly knowledgeable about biology, do you study a biology based degree?
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CTLeafez
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Adding to that others have mentioned, even with 99.9% similarity, that remaining 0.1% is still a large number of nucleotides (the monomers which DNA is made up of )

Humans have approx 3 billion nucleotides per genome (all the genetic material of the cell), 0.1% of 3 billion is 300,000, that's 300,000 differences in the genetic code between you and your friend!
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Jpw1097
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(Original post by Anonymous1502)
You seem incredibly knowledgeable about biology, do you study a biology based degree?
I study medicine, so I’ve covered basic sciences during my first two pre-clinical years including genetics. It’s quite relevant when it comes to cancer in particular.
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CTLeafez
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(Original post by Jpw1097)
First, not all DNA codes for proteins. A large proportion of DNA is non-coding DNA. Even within genes (regions of DNA that code for proteins) there are regions which do not code for proteins - these regions are known as introns.
Just to add another layer of complexity, the definition of a gene is 'a sequence of nucleotides which encode for a functional product.' once you get to a University onwards level. You can have genes which encode for RNA transcripts, which then can interact with proteins or other mRNA of other genes, regulating their translation

My current MSc proposes a mechanism by which this gene within bacterial meningitis is regulated by short non-coding RNAs (sRNAs).

They used to call this 'non-coding' DNA 'junk DNA' since it didn't have an obvious function, every year we're discovering loads of new stretches of DNA which actually do have a function!
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Anonymous1502
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(Original post by Jpw1097)
I study medicine, so I’ve covered basic sciences during my first two pre-clinical years including genetics. It’s quite relevant when it comes to cancer in particular.
I find cancer very interesting and I always wondered whether when we are born are people "destined" to develop cancer or is it mostly our lifestyle choices e.g. consuming large amounts of processed meat the cause? Also for childhood cancers is it mainly genetics what is the cause?
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helicopterbrawl
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We're not really that different. You're likely more similar to another human as opposed to a tree... or a golf ball.
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CTLeafez
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(Original post by Jpw1097)
I study medicine, so I’ve covered basic sciences during my first two pre-clinical years including genetics. It’s quite relevant when it comes to cancer in particular.
How far along are you into Med School? I shared the occasional lecture with the med students during my postgrad year.
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Jpw1097
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(Original post by CTLeafez)
Just to add another layer of complexity, the definition of a gene is 'a sequence of nucleotides which encode for a functional product.' once you get to a University onwards level. You can have genes which encode for RNA transcripts, which then can interact with proteins or other mRNA of other genes, regulating their translation

My current MSc proposes a mechanism by which this gene within bacterial meningitis is regulated by short non-coding RNAs (sRNAs).

They used to call this 'non-coding' DNA 'junk DNA' since it didn't have an obvious function, every year we're discovering loads of new stretches of DNA which actually do have a function!
Absolutely. Genetics is an incredibly complex field, I don’t even pretend to understand it to a high level. As you say, lots of non-coding regions may alter the expression of other genes.
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CTLeafez
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(Original post by Jpw1097)
Absolutely. Genetics is an incredibly complex field, I don’t even pretend to understand it to a high level. As you say, lots of non-coding regions may alter the expression of other genes.
I'm about 1,000 words away from finishing my MSc and I'm still not any fraction of an expert either :') . 'Genetics' in itself is a quite broad topic when you really start learning the inner details of specific areas.
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Jpw1097
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(Original post by CTLeafez)
How far along are you into Med School? I shared the occasional lecture with the med students during my postgrad year.
Just finished my fourth year . Taking a year out to do a BSc which is laboratory based. Sounds like an interesting MSc!
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CTLeafez
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(Original post by Jpw1097)
Just finished my fourth year . Taking a year out to do a BSc which is laboratory based. Sounds like an interesting MSc!
Congrats! I don't blame you, I was gonna have a year off before doing a PhD but then I stumbled across some interesting projects...

You get a BSc from just a year of laboratory work? Did you passively gain 240 credits towards the BSc over the previous 4 years?
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tazarooni89
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(Original post by Leah.J)
This question has been confusing me for the longest time, but I never really made an effort to understand, so here I am.

I don't understand how I can be 99.9% identical to a friend when every physical feature between us is different. I have curly hair she has straight hair, I am 5'9 she is 5'5, I have brown eyes , she has hazel, I have smaller bones and less muscle and she has wider bones and a lot of muscle... how is our genetic data so similar ?
The DNA that we both have exact copies of, what does it code for ?

And I recently learnt that a polymorphic gene is a gene which has more than one allele in the population.. doesn't this mean that the 0.1% of genes that make us unique are all polymorphic ?
The gene that codes for eye colour is polymorphic , true ?

Is an example of the gene that is not polymorphic the gene that codes for RNA polymerase ?
It’s because our differences are more noticeable than our similarities.

You might notice that your friend has a different hair colour to you, but much more easily pass over the fact that they have the same number of arms as you, or has lungs like you instead of gills etc.
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