eh I'd written a nice long reply.... and then my computer shut down grr. I wish i'd kept my biology books from school instead of selling them, this is all off the to of my head... it's good fun remembering it all though.
Sigh. Ok let's start that again.
Basically what I was saying is that the processes of independent assortment, crossing over and even fertilization all have an effect on variation, and maybe that's something these algorithm programs dont' properly take into account... I don't know because I don't have much knowledge of the programs, but there definatley is a lot more contributing to variation than simply random initial population or mutation.
I'll explain Meiosis, and how crossing over etc increase variation. If you already are familiar with it all then bare with me... I'm doing this off the top of my head from what I learnt in school last year. Eh on second thoughts i'm goig to type this in word so i can save it in case my comp fucks again.
Ok… Meiosis is the process of producing gametes (sex cells ie, eggs, sperm) from normal cells. A normal human cell contains 46 chromosomes, 23 maternal (passed on from your mother) and 23 paternal (passed on from your father). Right, when a cell is about to undergo Meiosis 1 stage of Meiosis the maternal and paternal chromosomes all pair up in homogulous pairs. This means that say… chromosome 10 from the paternal side pairs up with the corresponding chromosome 10 from the maternal line.
When they are in their homogulous pairs, they do what is called ‘crossing over’ (no, they don’t talk to dead people). In crossing over, a random piece from the paternal chromosome is snipped off and exchanged with the corresponding piece from the maternal chromosome. Despite both of the pieces being corresponding, they contain different genetic information, thus ensuring that each chromosome is mixed around. This exchange of information happens at random, and to each of the 23 homogulous pairs. As you can probably see from this, already the chances of any two offspring being genetically the same has been reduced enormously, thus creating more variation.
After crossing over, the homogulous pairs line up along the middle of the cell, creating two lines of 23 chromosomes, side by side. Now as they line up along side each other they go through another process called ‘independent assortment’. Basically this means that as the chromosomes form the two lines, they do so independent of each other, meaning that all the 23 paternal chromosomes will not try and form in the same line. The result is that both lines contain a mix of both maternal and paternal chromosomes so that when the cell splits in two both of the new cells will have a further mix of genetic material.
So there are two cells, both haploid (23 chromosomes). They contain a mix of genetic material, and when they undergo Meiosis 2 stage - which is a further splitting of the cells – they will each have vastly different genetic makeups. Now every chromosome in a normal cell is made up of two ‘Sister Chromatids’ connected at the middle (the Centromere), thus forming the distinctive X shape. Normally, as their name suggests, Sister Chromatids are simply two copies of the same genetic information. In Meiosis and the formation of sex cells they are changed due to the process of crossing over, so that one of the Chromatids will contain different information to the other. When the cells undergo the splitting of Meiosis 2, the result is four gametes, each with significantly different genetic information.
We now have four gametes with randomly selected genetic information from the maternal and paternal chromosomes, with the information of one cell divided and mixed into four. The chances of any two offspring ever being identical are now even lower. Keep in mind that during this whole process, mutation could have formed very easily, thus contributing entirely new information.
We now come to the final and certainly the most pleasurable stage of sexual reproduction – fertilization. Now we have a huge number of factors coming into play; not only do we have the complete randomisation of the sperm cells, but the whole process of Meiosis has also happened to produce the eggs of the female. If we took just one egg and one sperm to form a zygote (fertilized cell) then the chances of being able to produce another genetically identical zygote are mind-blowing. Then you consider that simply the time of fertilization plays a part, determining whether one egg is fertilized one month or a different egg another month. On top of this we have the millions of sperm, and the chances of one sperm fertilizing the egg over another.
So… take a step back and a deep breath. What are the chances of a man and a woman producing two genetically identical offspring from separate fertilizations? Well I’d go so far as to say it is impossible. A woman produces something like 56 eggs from puberty to menopause, and not ever single one of these is able to be fertilized… a man will produce millions of sperm in his lifetime, yet only a small fraction will ever do what it was intended for.
From this we see that even between two people the amount of genetic variation possible is enormous, mind-blowingly enormous, as genetic information is randomised, mixed and matched. Also, I think each person should feel very lucky to be alive haha.
Well that’s my very long-winded explanation… sorry if it’s hard reading it all, but the whole process of Meiosis is so complicated that it takes a lot to bend your mind around it (zygote, haploid, diploid, meiosis 1, meiosis 2, independent assortment, crossing over, chromatids… ehh it’s a wonder I ever memorized it all for my exams.) I love biology for the reasons that everything that looks simple is actually so damn complex, and whey you understand the complexity it gives you a completely different look on life.
But yeah… there definitely is a lot more to variation than population and mutation . This isn’t even talking about the fact that in the offspring some of the genes will be dominant or recessive, ending up with a entirely different individual than the genes might suggest.
That’s all for now lol.
|
|
Bookmarks