Thread: Help on DNA

I keep reading that all humans share 99% of their DNA with all other humans. However I've also read that children have 50% of their parents genes (I don't need any further information on the percentage of genes that we share with close relatives as I already understand this). My question is, what do we mean when we say, all humans share 99% of their DNA but parents share 50% of their genes with their children.

Good question!

The 99% figure is about the amount of variation between people. We have 99% of our genes in common; it this 99% that makes us human, rather than gorillas or slime mould. The 1% is what makes us who we are: eye color, height, etc. [Actually, I think the variation among humans is much less than that. I think we have 99% in common with other apes]

As for the 50%, that is where we get our particular set of genes (both the 99% and the 1%) from.

Imagine the genes as a very large deck of cards. In humans the cards are nearly all the same, a small proportion (1%) vary slightly. Now take two of these decks of cards and create a new deck by taking (approximately) half from one deck and half from the other. You know have a new deck with the same 99% in common, but with some cards from each parent deck.

"Oh look, he's got his father's nose"
"Yes, and his mother's mouth"

Hi Conjl,

Strange is absolutely correct.

I don't know how familiar you are with the genetic code, but essentially the genome of any given organism contains a digital information code that can be denoted by the letters A, C, G, T (bases). The genomes of several organisms can be aligned to determine homology (that is, the degree to which the codes are similar):

F5.small.gif

At the population level, if we were to align the genome sequences of two humans, we would expect them to have different bases at 1 position in every 100, on average. Does that make sense? This is what we mean when we say that humans share 99% of their DNA.

On the other hand, what we mean when we say that parents hare 50% of their genes with their children, is that they have physically passed on half of their genetic material via the process of meiosis and subsequent fusion of sperm and egg to create the zygote (future child):

meiosis.jpg

Please let us know if you need any more information.

Best wishes,

Tridimity

Links

Sequence alignment - Sequence alignment - Wikipedia, the free encyclopedia
Meiosis - Meiosis - Wikipedia, the free encyclopedia
Fertilisation - Fertilisation - Wikipedia, the free encyclopedia

Please ignore my first point - single nucleotide polymorphism (SNP) rate between two randomly chosen people is estimated to be ~0.1% (1 difference per 1,000 base pairs) NOT 1% (1 difference per 100 base pairs).

Sachidanandam et al (2001) Nature

A map of human genome sequence variation containing 1.42 million single nucleotide polymorphisms : Article : Nature

Originally Posted by conjl

I keep reading that all humans share 99% of their DNA with all other humans. However I've also read that children have 50% of their parents genes (I don't need any further information on the percentage of genes that we share with close relatives as I already understand this). My question is, what do we mean when we say, all humans share 99% of their DNA but parents share 50% of their genes with their children.

I think you misread that. Humans share 100% of their DNA with most living beings. The DNA sequence and organization of chromosomes and other genetic elements is where the differences lie.

Thanks for the help everyone. So my understanding is that all humans share 99 + % of their type of genes, however the exact version (allele) varies among individuals and we inherit 50% of this varience from each parent. So if all my genes are not exactually the same as yours, as they all have at least one different base pair in the position of one of your base pairs, it is right to say that me and you share 0% our genes, even though over 99% of the genetic code in our genes is identical. So 99 + % of human genes have the same sort of function (e.g coding for eye color) but they are not essentially the same gene. Hopefully I'm on the right track here. I'm not really too sure though what spuriousmonkey is talking about.

Originally Posted by conjl

Thanks for the help everyone. So my understanding is that all humans share 99 + % of their type of genes, however the exact version (allele) varies among individuals and we inherit 50% of this varience from each parent. So if all my genes are not exactually the same as yours, as they all have at least one different base pair in the position of one of your base pairs, it is right to say that me and you share 0% our genes, even though over 99% of the genetic code in our genes is identical. So 99 + % of human genes have the same sort of function (e.g coding for eye color) but they are not essentially the same gene. Hopefully I'm on the right track here.

Pretty much, I think.

I'm not quote sure what your "share 0% our genes" bit meas. Obviously my genes are different from yours in that mine are in my cells and yours in yous! But most of the genes are identical.

I'm not really too sure though what spuriousmonkey is talking about.

I think he is making the distinction between DNA (which is identical everywhere) and the genome of each organism (which is different).

Well what I was saying with the "share 0% our genes" part was that once a gene has changed in anyway, it becomes a new gene. So if my gene for eye color is one base pair different to your gene for eye color then are we saying they are different genes even though they have the same function? If yes, then pretend that every gene in my body is at least one base pair different to everyone gene in your body. Could i say that I we share 0% of our genes?

Originally Posted by Strange

Originally Posted by conjl

Thanks for the help everyone. So my understanding is that all humans share 99 + % of their type of genes, however the exact version (allele) varies among individuals and we inherit 50% of this varience from each parent. So if all my genes are not exactually the same as yours, as they all have at least one different base pair in the position of one of your base pairs, it is right to say that me and you share 0% our genes, even though over 99% of the genetic code in our genes is identical. So 99 + % of human genes have the same sort of function (e.g coding for eye color) but they are not essentially the same gene. Hopefully I'm on the right track here.

Pretty much, I think.

I'm not quote sure what your "share 0% our genes" bit meas. Obviously my genes are different from yours in that mine are in my cells and yours in yous! But most of the genes are identical.

I'm not really too sure though what spuriousmonkey is talking about.

I think he is making the distinction between DNA (which is identical everywhere) and the genome of each organism (which is different).

If one gene is called A, then does a version of the gene that is one base pair different to A get the same name - A?

Originally Posted by conjl

Well what I was saying with the "share 0% our genes" part was that once a gene has changed in anyway, it becomes a new gene. So if my gene for eye color is one base pair different to your gene for eye color then are we saying they are different genes even though they have the same function? If yes, then pretend that every gene in my body is at least one base pair different to everyone gene in your body. Could i say that I we share 0% of our genes?

The genes for different eye colour, say, are the same genes, there are just different forms (alleles).

If every gene in your body was different then you wouldn't be human! There are only a small number of the genes that vary between people.

This might be useful: http://en.wikipedia.org/wiki/Introduction_to_genetics

Originally Posted by conjl

If one gene is called A, then does a version of the gene that is one base pair different to A get the same name - A?

Yes, it has the same name. The variant (allele) is indicated with a suffix. e.g. PGM might be the gene and PGM*1 a particular allele.

Gene nomenclature - Wikipedia, the free encyclopedia

Ok so when we say we share 50% of our genes from each parent we are saying that we have 50% of our mothers alleles and 50% of our fathers alleles.

Anyway, thanks again for all the help.

Originally Posted by conjl

Ok so when we say we share 50% of our genes from each parent we are saying that we have 50% of our mothers alleles and 50% of our fathers alleles.

Well, we have 50% of the total DNA from each, which will include (on average) 50% of the alleles from each.

As I was writing some of those replies, I discovered a big "hole" in what I know; stuff I used to know that has just completely disappeared. Spooky. Time to do some reading....

Ok thanks. By the way, have you read 'The Selfish gene' because the 6th chapter 'Genesmanship' is what made me ask the questions.

No, I'm afraid I haven't read it.

Hi Conjl,

I've read 'The Selfish Gene', although it's been a while since I read so although I remember the overall thrust of the book, I don't remember specifically the chapter on 'Genesmanship'. Would you like to discuss it?

Tridimity~

DNA Dielectric Properties

Human telomeric DNA is composed of tandem repeats of the TTAGGG sequence bound to an array of proteins (Blackburn, 2001; Chan and Blackburn, 2002; De Lange, 2002). These repeats are shortened at each cell division. Therefore normal human somatic cells have a limited proliferate capacity. In contrast, immortalized cells do not exhibit telomeric shortening due to the presence of telomerase (Shimojima et al., 2004). Telomerase is a ribonucleoprotein complex with transcriptase activity (Morin, 1989; Maser and Depinho, 2002), responsible for restoring telomere length in dividing cells (Allsopp et al., 1984; Bryan and Cech, 1999). High telomerase activity was detected in the majority of human tumors; whereas low or undetectable activity was found in differentiated cells of the homologous normal tissue (Kim et al., 1994; Broccoli et al., 1995; Wright et al., 1996). Therefore, detection of telomerase activity can be considered a biochemical signal for the presence of various cancer cells, the level of this enzyme activity may represent a new type of cancer marker (Dario et al., 2005). Recently, three components of the telomerase have been cloned; human telomerase RNA component (hTERC), which is used as a template in DNA replication (Feng et al., 1995); human telomerase reverse transcriptase (hTERT), a human telomerase catalytic sub unit (Nakamura et al., 1997) and human telomerase associated protein 1 (hTEP1) of unknown function (Harrington et al., 1997). It has been reported that hTERT mRNA expression is significantly correlated with telomerase activity (Zhang et al., 2001). These data strongly suggest that hTERT is probably the rate-limiting component for enzyme activity.

The development of new molecular approaches in biology and biotechnology introduced new scientific terms which include genome, genomics, methylome and methylomics

Hey tridimity thanks for the offer. I was just saying that my question arose when I was reading about the relation between close family members such as parents and children or siblings in the chapter 'Genemanship' from 'The Selfish Gene'. I think my questions were answered by strange, however if you read my comments and think that I havn't fully understood anything then I would appreciate any help.

Thanks for the offer tridimity. I think strange answered my questions. However, if you read my last few comments and think that I still don't fully understand the genetic relationship between parents and their children from the chapter 'Genemanship' in 'The Selfish Gene', or anything else, then I would appreciate some help.

Ignore the unregistered post. I didn't rearlise I wasn't logged in.