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Mendel's experiments with pea plants.

  1. Mar 11, 2004 #1
    In my bio class, we're learning about genetics currently and watched a video demonstrating mendel's experiments with pea plants. Something in the video didn't seem right to me, and my biology teacher is horrible and couldn't understand my question.

    In the part of the video in question, it shows a plant which had been bred from one parent which was pure bred so that it's peas were smoothe, and one parent which was pure bred so that it's peas were wrinkly. In the F1 generation, the peas were all smoothe. To demonstrate that the recessive wrinkly pea gene hadn't dissapeared, they showed a plant which had been bred from 2 plants which were swinkly/smoothe hybrids. This plant had 3 smoothe peas and 1 wrinkly pea in the same pod. This was to demonstrate the 3 to 1 ratio that smoothe peas had to winkly peas when bred from 2 hybrid parents.

    However, the thing that confused me was the fact that there were 2 different types of peas in the same pod. I understand how if you beed 2 hybrids that you have a 75% chance of getting the dominant factor, but I didn't think that the dominant and recessive factors would show up partially in the same organism. To me, having 3 smoothe and 1 wrinkly pea in the same pod seemed like someone having 25% red hair and 75% black hair.

    So, is it possible to have wrinkley and smoothe peas in the same pod, or was that specifically planned that way to demonstrate a principle?
     
  2. jcsd
  3. Mar 12, 2004 #2
    I remember seeing that same picture. My understanding was it was only to demonstrate the 3 to 1 ratio.

    Nautica
     
  4. Mar 12, 2004 #3
    Yeah, you've got to remember that those peas are now the F3 generation. The F2 plant is heterozygous for the smooth an wrinkly gene, it's descendants (i.e. it's peas) will be 1/4 wrinkly.
     
  5. Mar 12, 2004 #4
    But that means that 1 out of every 4 plants will be totally wrinkly, and 3 out of every 4 will be totally smoothe, and none will be partially wrinkly and partially smoothe (assuming no sort of mutation), right?
     
  6. Mar 12, 2004 #5
    right.
     
  7. Mar 12, 2004 #6
    Thanks nautica and Chemicalsuperfreak!
     
  8. Mar 13, 2004 #7

    Monique

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    Ok, I am not an expert on pea plant fertilization.. but peas in a pod are seeds that have been fertilized. If you have an 'Aa' heterozygotic plant crossed with an 'Aa' heterozygotic plants you get the following.. 'eggs': A and a's, and the following 'sperms': A and a's.

    So basically in the undeveloped pod there is a mixture of A's and a's, that get fertilized by a plant with a mixture of A's and a's.

    So: NO, there is no such thing as 1 out of four plants totally wrinkled and 3 out of 4 totally smooth. The peas of the single plant will have 1/4 wrinkeled and 3/4 smooth peas.
     
  9. Mar 13, 2004 #8
    So, you and nautica seem to be in disagreement, now I'm confused.
     
  10. Mar 13, 2004 #9

    Monique

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    Peas are seeds that grow from eggs fertilized by pollen, they grow from two 'parents' (actually: in the pea plant, self-fertilization occurs mostly).

    I found the following website which explains the same thing as I understand it too:
    http://www.fathom.com/feature/122612/

     
  11. Mar 16, 2004 #10
    I was going off memory of the picture. I will have to go with monique on this one, since it looks like she took the time to look it up.

    nautica
     
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