DNA - How Different Genes Coexist in Our Bodies

[Dal]

So,... this strands of DNA is what makes everyone of us unique and they're in every organs, tissues, blood...etc right? When there is an organ transplant, the part(or organ) that you're accepting has its own genetic stature so doesn't the body reject the new part? Once you acquired a new organ, how does your body and the organ having different genetic ID coexist without problem?

 

[Monique]

Hi Dal, actually all of us have the same genes.

The thing that makes us unique is the version of the gene, there are slight mutations from person to person which change some of the characteristics, which makes us different.

The cells of our bodies are able to recognize which cells our ours and which ones are foreign (invaders). An organ that is transplanted is thus also recognized as foreign, UNLESS it is from a family member (rejection rates in that case are lower).

Doctors actually have to force a body to accept a foreign organ, they do this by surpressing the immune system (which acts to recognize foreign things and attack it). They have to give very large doses in the beginning, but this also leads to infections. Thus slowly they start to lower the dose and hope that all goes well.

It DOES mean that someone with a transplant will have to be on immuno supressant therapy for the rest of its life.

 

[fish]

I thought a mutation was more of a chance happening (rare) while the meiosis process was more of the programmed 'absolutely will happen'? Many mutations arise spontaneously when DNA is replicated or by radiation, carcinogens, etc. but repair enzymes try to restore these altered base sequences.
DNA is in the nucleus of all your cells. During meiosis (sexual reproduction) 2 things occur that make people unique: crossing over at prophase I (swapping segments of 2 nonsister chromatids of pairs of homologous chromosomes - between the mother and father) and metaphase I random alignment of the homologues. this varies the genes with new combinations of alleles or variation in traits of offspring. genetic recombination- combos of alleles in chromosomes not present in the parental cell. Human germ cells have 23 pairs of homologous chromosomes, so when a human germ cell forms sperm or eggs, there are 2^23 (over 8 million) possible mom and dad combinations of chromosomes. Mendel's independent assortment theory shows that if parents differ in say 20 gene pairs, the genotypes possible are near 3.5 billion (3^n or 3^20)

 

[Dal]

Thanks for answering. So, the body can accept a new part once the immune system is weakened. Say, after the transplant, we take a cell sample of a new organ and read its DNA, does the stracture(sequence) differ from your body's DNA sequence? or does it somehow re-sequence the DNA stracture to match the rest of the body?

 

[Monique]

Well, DNA is a very long string which contains a code made up of four letters: A, G, C and T. In total there are 3 billion of those letters on 23 paired chromosomes (46 in total) but it is believe that there are 'only' about 30,000 genes.

This genetic material is located in the nucleus of all the cells in your body (there are a few cells which loose it though, such as red bloodcells).

So to answer your question, yes, an organism can accept a foreign organ when the immune system is weakened.

But no, the DNA of the organ or the host won't change. The resequencing you suggest would just be too complex to carry out and doesn't hold any evolutionary advantage (at least, not up until this age where we are doing this kind of treatment).