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Homozygosity question

  1. Nov 24, 2014 #1
    What does this mean-plants are self-pollinated for few successive generations to get homozygosity.
    My attempt-i think ,say a plant is heterozygote Pp for a trait
    self pollination Pp ×Pp
    F1=50% Pp,25%PP,25%pp
    so,it is possible for many crosses hybrid may be obtained from that 50% Ppi.e so heterozygote so to get homozygosity.i.e either Pp,25% or PP,25%pp we may need to cross again and again for few successive generations .right?
     
  2. jcsd
  3. Nov 24, 2014 #2
    Self pollinating again with the F1 and noting the phenotypes of the offspring is a good method of figuring out the genotypes of your F1 plants. If you self pollinate with one and get only pp as an F2, you can be pretty sure you isolated the pp F1 plant. If you only get PP as an F2, you can be pretty sure you isolated the PP F1.
     
  4. Nov 24, 2014 #3

    Ygggdrasil

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    Consider a plant that is heterozygous at only 10 loci. After self pollination, if you look at one progeny, five of its loci (on average) should now be homozygous and five should remain heterozygous. If you self pollinate that F1 plant, its progeny should (on average) retain only 2.5 heterozygous loci (since all homozygous loci will breed true and remain homozygous). You should be able to see how repeating this process of isolating an individual from a cross and self-pollinating that individual to create the next generation will generate a plant with fewer heterozygous loci.
     
  5. Nov 25, 2014 #4
    ok can you please explain difference between breed and species.sometimes breed means mate and then produce offspring.but i am not talking about that.In Wikipedia on topic crossbreeding there is written - crossbred usually refers to an organism with purebred parents of two different breeds, varieties, or populations.how these two underline words differ?and difference between breed and species?
     
  6. Nov 25, 2014 #5

    Ygggdrasil

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    A breed (a term primarily used for animals) or variety (a term primarily used for plants) can be considered an informal classification below the level of species. Most definitions of the term species will say that when members of the same species mate, they will be able to generate a fertile offspring while when members of different species mate, they will not be able to generate fertile offspring (they may be able to generate infertile hybrids, such as mules, however).

    Breeds and varieties occur because of selective breeding that tends to create members of the same species that have very different characteristics. Purebred lines are those that have been inbred so that most of their genes are homozygous. Therefore, breeding two purebred individuals from the same breed will produce an offspring with the same characteristics as its parents. A crossbred is heterozygous at many of its loci, so even if you breed two crossbred individuals with the same characteristics, its offspring likely will not share the characteristics of its parents. A good example of this is apple varieties. All apple varieties are the result of crossbreeding, so if you plant an apple seed that came about from self-fertilization, the resulting apple tree will not produce apples that are the same those from the parent apple tree. This is why apple varieties must be propagated by grafting.
     
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