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Gregor Mendel’s Luck

23 May

Gregor Mendel

Gregor Mendel was a nineteenth century monk widely known for his work with peas and genetics. It was his work in the abbey gardens that lead to the rules for simple inheritance. The Law of Segregation states that when an organism is producing sex cells (eggs and sperm) each cell gets one and only one copy of the genes. The Law of Independent Assortment states that each pair of genes divides independently of other genes. What copy or allele of gene A you get has no effect on which copy of gene B.

And although his work was lost for many years before being rediscovered in the twentieth century and later fused with Darwin’s ideas of natural selection, Mendel’s work sets him apart as a giant upon whose shoulders we have built our knowledge of biology.

However, the funny thing is, Mendel got pretty lucky.

Firstly, the Law of Segregation assumes that each organism only has two copies of a gene. And for the majority of plants and animals this is correct. However, there are exceptions. The peas he worked with do, in fact, have 2 sets of chromosomes (this is known as being diploid, or a 2N organism). However, other nearby plants were not. Apples can have an odd number of chromosomes (3N). Tobacco is a tetraploid (4N). Domestic oats are hexaploid (6N). Strawberries may have as many as eight copies of their chromosomes! It was quite fortunate that Mendel didn’t turn his attention to these plants since their crosses can get more complicated.

Freaks

Secondly, we now know that the Law of Independent assortment is not an absolute rule. When Mendel was working he assumed that each gene was free-floating and totally free from any other gene. This is not correct. Genes are tied together through their sequences into large collections of proteins and DNA known as chromosomes. And while chromosomes can switch around their genes with neighboring sister chromosomes during sperm or egg development, genes that are too close can affect each other’s chances.

Mendel worked with seven visible traits when he looked at peas. Each one just happened to be on a different chromosome and free from any possible interference. It would have been terribly easy for him to choose a trait that would not have been so easily understood. One of his laws may have never even gotten off of the ground.

Mendel was, overall, correct in his observations and the creation of his laws. However, it is quite amusing to sit back and consider just how lucky he was.

Sources: RNCWikimedia

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7 Comments

Posted by on May 23, 2011 in Biography

 

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7 responses to “Gregor Mendel’s Luck

  1. Ernie Bornheimer

    May 26, 2011 at 1:30 pm

    I seem to remember reading that luck had nothing to do with it, but rather that Mendel made conscious decisions to only include examples where the principles/rules obviously worked.

    Great blog, keep it up!

     
    • theglyptodon

      May 26, 2011 at 1:37 pm

      Thanks, glad you enjoyed it.

      I seem to remember that Mendel’s results regarding the Independent Assortment were suspiciously close to the proposed 3:1 ratio, so there’s been some debate that he was victim of confirmation bias. I may also need to go back and change the Independent Assortment section altogether though, since I was writing about a criticism that was, itself, criticized. Hmm. Thanks for pointing that out.

       
  2. Fictitiousname

    July 20, 2012 at 8:41 pm

    It is not correct to say that all the traits where not licked (locus for 2 traits are not on the same chromosome. They were not genetically linked.

     
    • theglyptodon

      July 20, 2012 at 9:18 pm

      Hmm. I’ll double check what I wrote. Thanks for pointing this out.

       
  3. Fictitiousname

    July 20, 2012 at 8:42 pm

    *linked

     
  4. Nanayaw

    December 16, 2014 at 1:34 pm

    why was Mendel was considered lucky in postulation of his theory of particulate inheritance

     
    • theglyptodon

      December 16, 2014 at 1:42 pm

      I meant for this post to point out that genetics, especially among plants, can sometimes be quite complicated. And even though Mendel was correct, if he had been working under different circumstances, it might have taken him a lot longer to come to the correct conclusion.

       

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