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Determination of individuality

  1. Dec 20, 2014 #1
    Which cell makes you ‘you’(different from any other individuals of the same sex)somatic or sex cells?I think somatic cells.Because if i am right all somatic cells are same ,so it can be determinant for making an individual but sex cells (I don’t know about egg cell but as i have studied about sperm cell ,all sperms are quite different)So how can these cell decide or be basis for making an individual ?So sexc cells only decide which information we will be giving off or what our progeny would be not what we are!RIGHT?And yes of course sex cells will be responsible for sex linked inheritance.
     
  2. jcsd
  3. Dec 20, 2014 #2

    Drakkith

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    There is no one thing that makes you different from another person. It's a combination of many different factors, not the least of which is the way your brain grows (some of which is independent of DNA) and the things you are exposed to during life.
     
  4. Dec 21, 2014 #3
    As noted by Drakkith, there are a multitude of factors that make each person distinct from a biological point-of-view. Each cell in your body, whether it be a somatic or sex cell, is different from the same cell types in other individuals for a variety of reasons. First, let's begin with your DNA:

    Most of your cells contain the same DNA. DNA can be considered effectively as an "alphabet" of four letters, A, T, C and G. These letters selectively pair with one another, so that A only pairs with T and C only pairs with G. These A-T and G-C pairs are known as base-pairs, and it is the unique sequence of 3.3 x 10^9 of these base-pairs that makes up your genome. This means that everyone who is not an identical twin has a unique sequence of DNA (or "genome"), and that plays a large part in what makes individuals unique.

    However, that is nowhere near the full story. How can it be, when you consider that cells in your skin, eyes, stomach, heart, liver, kidneys, and even intestines share the same DNA yet differ so much in appearance and function? The answer to that lies in what is known as gene expression, i.e. the selective transcription / translation of parts of your DNA into proteins. Proteins are the biological molecules that carry out most of the functions in your cells. The unique sequence of DNA in your genes determines the structure of proteins they "code". Proteins also bind to pretty much every part of your DNA on your genome. Which proteins bind to your DNA and where affects how much of the bound DNA is "expressed" (i.e. how much ends up translated as proteins). A different set of DNA-binding proteins in each cell type allows only particular combinations of genes (specific to the particular cell in question) to be expressed as proteins. This is how cells containing the same DNA differ so much.

    The study of how factors other than DNA sequence affect how your genes are expressed and inherited is known as epigenetics.

    So, that goes a long way towards explaining why cells within your body can be so different despite having the same DNA. But what about what makes you, as an individual, unique? Well, the answer is very similar. You already know that your DNA sequence is unique, but the combinations of proteins that bind to your DNA and regulate its expression are also unique. These are a form of epigenetic marker, and vary from person to person. They are affected by everything from your diet to everyday life experiences, such as happiness or stress. Studies have shown many of these epigenetic markers are different in identical twins, who have the same DNA.

    The final piece of the puzzle is your development, particularly brain development. Your brain has developed (and continues to develop) a complex 3-D network of communicating neurons. The structures of these networks affect brain function, and are influenced by many factors (again, e.g. diet, stress, exercise etc..).

    So, in summary:

    There are an almost unimaginable number of factors influencing your biological development, each of which contributes to making you unique. Your unique DNA sequence, unique set of epigenetic markers and unique development all make you a truly individual. The first and last exact version of you ever to exist on this planet. No one cell makes you "you", every single one of your cells does!
     
  5. Dec 22, 2014 #4
    Ok.But i want to ask about sex cells.They contain genes quit different from that of somatic cells,as they are result of crossing over during process of meiosis.So thses cells would decide what we will pass in our offspring rather than what are we,right?
     
  6. Dec 22, 2014 #5

    Drakkith

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    Of course.
     
  7. Dec 22, 2014 #6
    Are all egg cells (female gamete)differ from each other?
     
  8. Dec 22, 2014 #7

    Drakkith

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  9. Dec 22, 2014 #8
    One more question .Human female diploid cells have 22 pairs of homologous chromosomes and two xx sex determining chromosomes.and (males have 22 pairs of chromosomes and one x and one y).These two xx sex determining chromosomes of female ,are they homologous?
     
  10. Dec 22, 2014 #9

    Drakkith

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    I believe so, but I don't know enough about DNA to be sure.
     
  11. Dec 22, 2014 #10
    I think DNA /genes of those two x chromosomes would be different as one comes from father and from mother.
     
  12. Dec 22, 2014 #11
    The two X chromosomes are different, correct. However, as you hinted at earlier, there has to be a mechanism to make up for the fact that males have only one X chromosome and females have two. Any one cell in your body only requires one X chromosome to be active, so if females had two active X chromosomes the result would be over-expression of X-linked genes, which would probably be lethal.

    To fix this "problem", we have evolved a way to inactivate one of the female X-chromosomes in every cell. Basically, the extra X-chromosome in females is wound up really tightly and coated in RNA to prevent its expression. This inactivates the whole chromosome, forming what is known as a "Barr body". The inactivation is random in each individual cell, meaning that females have a "mosaic" of X-chromosome expression throughout their bodies, with 50% of their cells inactivating one X, and the remaining 50% inactivating the other.

    This is why, if you clone a female calico cat with two colours on its coat, the pattern of colours won't be the same on the cloned individual. The gene for coat colour is X-linked, so which variant is expressed will depend entirely upon the pattern of X-chromosome inactivation, which is totally random
     
  13. Dec 22, 2014 #12
    Can you please reply to my 8th post.
     
  14. Dec 22, 2014 #13
    The two female X chromosomes are homologous, yes. However, they are not exactly the same (differ in DNA sequence, etc..)
     
  15. Dec 22, 2014 #14
    Thanks.
     
    Last edited: Dec 22, 2014
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