10
Nov
09

Mendelian Inheritance

Many people think genetics works like this.

While it is certainly a wonderful joke, this isn’t exactly what happens. Indeed, Dawkins devotes a few pages on this in The Greatest Show on Earth. Mendel actually discovered something contrary to the “blending of traits.” As Dawkins states, if traits were indeed a mix of the traits of each parent, we would see children with a combination of the traits of both parents, grandchildren would receive traits from all four grandparents, and, very quickly, diversity would decrease to a homogeneous blend. Dawkins uses the “mixing paint” metaphor. If you mix red paint and blue paint to get purple paint, no quantity of mixing will ever yield the original red or blue paint again.

So what, exactly, are the Mendelian laws?

The Law of Segregation states that when gametes are formed, the specific traits previously inherited from the parents are separate entities and are segregated from one another with only one of the two being inherited by offspring from each parent.

The Law of Independent Assortment states that traits from the same parent are not linked to one another. This means that the offspring can inherit a trait from one parent and a different trait from the other parent. While many genes are technically not “dominant” or “recessive,” traits can be. Most often, genes are coexpressed in differing cell populations or, sometimes, in the same cell. The traits resulting from one specific allele can appear to mask the traits of the other allele.

This is a point which needs further clarification in the very near future.

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9 Responses to “Mendelian Inheritance”


  1. 1 Pliny-the-in-Between
    November 10, 2009 at 2:47 pm

    The traits resulting from one specific allele can appear to mask the traits of the other allele.
    ——-

    Sickle cell trait is a great example of this in my opinion.

    I still laughed my — off at Stacy’s pic too but 4 kids might have provided a better illustration 😉

  2. 2 jaredcormier
    November 10, 2009 at 2:59 pm

    I, too, had a good laugh, but it was a combination of SMBC and that photo that made me feel the need to rant about Mendelian inheritance.

  3. 3 Colloquy
    November 10, 2009 at 3:05 pm

    That wasn’t a rant! You must be very mild mannered! :evil:!

  4. 4 Colloquy
    November 10, 2009 at 3:06 pm

    Oops! wrong smiley! :mrgreen:

  5. 5 jaredcormier
    November 10, 2009 at 3:13 pm

    Usually, I’m quite mild mannered, although some things do elicit much stronger reactions. These, however, typically come in the form of cranks and crackpots trying to take advantage of others by intentionally deceiving for personal gain.

    I think my most vitriolic responses are as a result of “faith-healers” and homeopaths taking money from the uninformed.

  6. 6 mac
    November 10, 2009 at 10:20 pm

    I like the paint analogy. Even a dummy can understand that – well, this one can, anyway.

  7. 7 jaredcormier
    November 10, 2009 at 10:36 pm

    It was rather nice; I read Dawkins for his metaphors, not because I learn anything particularly new, but because his metaphors are so useful.

  8. November 11, 2009 at 1:26 am

    A well turned metaphor can be a valuable tool in transfering concepts.

    From an engineering perspective, the forms of genetic transference which prevent blending analoguous to the paint metaphor reduces the probability of a genetic line painting itself into a genetic corner.

    Do I correctly understand the direction of your argument, or must I return to the drawing board?

    Oh, from the reference to engineering I do not imply intelligent design.

    Hmmm. On the other hand, perhaps I do.

    Mike

  9. 9 jaredcormier
    November 11, 2009 at 11:45 am

    Mike, I think you should return to the drawing board since organisms do “paint themselves into genetic corners” even with the non-mixing of alleles. Tasmanian devils are wonderful examples of low genetic diversity, but this is due to population bottlenecks. This paint metaphor is exclusively to illustrate what does not happen. An engineering perspective could look at paints as not actually changing molecularly when the paints are mixed. The individual pigments remain unchanged even when different paint colors are mixed.


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