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Disadvantage of self pollination

  1. Jan 10, 2013 #1
    hi

    i am now learning the topic "Reproduction in flowering plants" and i encounter something i don't understand

    It is said that there are two disadvantages for self pollination

    1. the offspring are genetically identical to their parents so becoming less adaptable to the environment.

    and

    2. The offspring are weakened with fewer seeds

    then it has no explanation about why. would anyone briefly explain it to me? why genetically identical would mean less adaptable to the environment ? What's the problem of being identical to their parents? I don't understand

    and why the offspring would be with fewer seeds? If their pollen grains go to stigma of another plants, they are also starting with a zygote only to do the mitosis on their own, why they will be with fewer seeds?

    No explanation available in the textbook

    Thanks
     
  2. jcsd
  3. Jan 10, 2013 #2
    1. Is sort of incorrect. It won't be identical, maybe it would have a simillar allele distribution, but the alleles in gametes would repeat or bring some mutations which are not in somatic cells. The problem with being identical to the parents is the lack of genetic recombination, which is the main force of preserving the species, letting the organisms to combine new mutations or produce natural selection in order to survive a harsh period in which the older members of the species aren't prepared for.

    2. With a similar to 1., if the plants would self pollinate, its offspring would carry almost all the same alleles, including the recessive, disadvantageous ones, specially the mutations. That means the offspring would be in a disadvantage, and the mutations would weaken them.
     
  4. Jan 10, 2013 #3

    jim mcnamara

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    Staff: Mentor

    There is an advantage to recombination of alleles when there are lots of heterozygous alleles (genetically different alleles). In this case the offspring will have a broad range of genotypes to deal with changing environments.

    Self pollinating plants plants over time tend to be more homozygous alleles with less genetic diversity. There also cannot be very much gene flow - there is no source of external alleles. The only genetic change "factor" is mutation.

    The fact that some species are either self pollinating or parthenogenetic and they are commonly found -- is that these species happened to be extremely well suited to a specialty environment.

    Dandelion (Taraxacum officinalis) is a very common weedy plant species in lawns. It does better there than do some grass species, much to the chagrin of homeowners...
     
  5. Jan 14, 2013 #4

    They are not genetically identical. However since there is good chance of being homozygous for a deleterious recessive allle. You might also want to check Inbreeding Depression


    Variation in a population is desirable; so that even if the population is doing pretty good in the current conditions, it will have a good chance of survival should environmental conditions change.

    Not sure why that would happen though.
     
  6. Jan 14, 2013 #5

    Evo

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    Staff: Mentor

    Don't forget that plants that can self pollinate can also cross pollinate with other plants of the same species. For example, tomatoes are self pollinating, but they can also cross pollinate with other tomatoes.
     
  7. Jan 14, 2013 #6
    The first statement is wrong. I am sure the textbook, or who ever made that statement, meant something else. In asexual reproduction, the offspring will have an identical genome to the parent. Selfing is not the same as asexual reproduction.

    If you draw Punnett squares for the selfing of a hybrid, in which a recessive gene is not expressed, you will see that a recessive gene has a good chance of being expressed in the offspring.There are three possibilities.

    The offspring of a parent that self fertilized itself would not be identical to its parent. At the very least, the chromosomes of the parent would be mixed up in the offspring. Some of the genes would get mixed up within the chromosome by cross over.

    The effect would be very similar to extreme inbreeding. The chromosomes of the parent are paired. The offspring would get a copy either one or the other chromosome in a pair. The offspring would also have paired chromosomes. However, the assortment of chromosomes in the offspring would be random.


    The off spring would get a double dose of some chromosomes, and zero dose of some chromosomes, and half and half mixture of some chromosomes.

    The effect would be like extreme inbreeding. Suppose the parent is a hybrid with respect to an allele in any chromosome pair. Suppose that one parental chromosome has a recessive gene and the other has a dominant gene. Obviously, the recessive gene won't be expressed in the parent. However, there is a 25% chance that the offspring will have a double dose of the recessive gene. The recessive gene will be expressed.

    If the recessive gene results in vulnerability to a certain disease, the results could be bad.
     
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