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  1. #1
    Australian Medical Marijuana Educator Smokin Moose's Avatar

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    Default Mendel's Basic Principles of Genetics

    There have been some recent posts regarding breeding cannabis, so I am posting this very basic explanation of principles of genetics. I hope it may be of help to newcomers.

    Mendel's Basic Principles of Genetics

    For thousands of years farmers and herders have been selectively breeding their plants and animals to produce more useful hybrids. It was somewhat of a hit or miss process since the actual mechanisms governing inheritance were unknown. Knowledge of these genetic mechanisms finally came as a result of careful laboratory breeding experiments carried out over the last century and a half.


    Gregor Mendel
    1822-1884

    By the 1890's, the invention of better microscopes allowed biologists to discover the basic facts of cell division and sexual reproduction. The focus of genetics research then shifted to understanding what really happens in the transmission of hereditary traits from parents to children. A number of hypotheses were suggested to explain heredity, but Gregor Mendel, a little known Central European monk, was the only one who got it more or less right. His ideas had been published in 1866 but largely went unrecognized until 1900, which was long after his death. His early adult life was spent in relative obscurity doing basic genetics research and teaching high school mathematics, physics, and Greek in Brno (now in the Czech Republic). In his later years, he became the abbot of his monastery and put aside his scientific work.


    Hybridized domesticated horses

    While Mendel's research was with plants, the basic underlying principles of heredity that he discovered also apply to people and other animals because the mechanisms of heredity are essentially the same for all complex life forms.

    Through the selective cross-breeding of common pea plants (Pisum sativum) over many generations, Mendel discovered that certain traits show up in offspring without any blending of parent characteristics. For instance, the pea flowers are either purple or white--intermediate colors do not appear in the offspring of cross-pollinated pea plants. Mendel observed seven traits that are easily recognized and apparently only occur in one of two forms:
    1. flower color is purple or white
    2. flower position is axil or terminal
    3. stem length is long or short
    4. seed shape is round or wrinkled
    5. seed color is yellow or green
    6. pod shape is inflated or constricted
    7. pod color is yellow or green

    Common edible peas
    This observation that these traits do not show up in offspring plants with intermediate forms was critically important because the leading theory in biology at the time was that inherited traits blend from generation to generation. Most of the leading scientists in the 19th century accepted this "blending theory." Charles Darwin proposed another equally wrong theory known as "pangenesis". This held that hereditary "particles" in our bodies are affected by the things we do during our lifetime. These modified particles were thought to migrate via blood to the reproductive cells and subsequently could be inherited by the next generation. This was essentially a variation of Lamarck's incorrect idea of the "inheritance of acquired characteristics."

    Mendel picked common garden pea plants for the focus of his research because they can be grown easily in large numbers and their reproduction can be manipulated. Pea plants have both male and female reproductive organs. As a result, they can either self-pollinate themselves or cross-pollinate with another plant. In his experiments, Mendel was able to selectively cross-pollinate purebred plants with particular traits and observe the outcome over many generations. This was the basis for his conclusions about the nature of genetic inheritance.


    In cross-pollinating plants that either produce yellow or green pea seeds exclusively, Mendel found that the first offspring generation (f1) always has yellow seeds. However, the following generation (f2) consistently has a 3:1 ratio of yellow to green.

    This 3:1 ratio occurs in later generations as well. Mendel realized that this was the key to understanding the basic mechanisms of inheritance.


    He came to three important conclusions from these experimental results:
    1. that the inheritance of each trait is determined by "units" or "factors" that are passed on to descendents unchanged
    2. that an individual inherits one such unit from each parent for each trait
    3. that a trait may not show up in an individual but can still be passed on to the next generation.

    It is important to realize that, in this experiment, the starting parent plants were homozygous for pea seed color. That is to say, they each had two identical forms of the gene for this trait--2 yellows or 2 greens. The plants in the f1 generation were all heterozygous. In other words, they each had inherited two different alleles--one from each parent plant. It becomes clearer when we look at the actual genetic makeup, or genotype, of the pea plants instead of only the phenotype, or observable physical characteristics.
    Note that each of the f1 generation plants (shown above) inherited a Y allele from one parent and a G allele from the other. When the f1 plants breed, each has an equal chance of passing on either Y or G alleles to each offspring.

    With all of the seven pea plant traits that Mendel examined, one form appeared dominant over the other. Which is to say, it masked the presence of the other allele. For example, when the genotype for pea seed color is YG (heterozygous), the phenotype is yellow. However, the dominant yellow allele does not alter the recessive green one in any way. Both alleles can be passed on to the next generation unchanged.

    Mendel's observations from these experiments can be summarized in two principles:
    1. the principle of segregation
    2. the principle of independent assortment
    According to the principle of segregation, for any particular trait, the pair of alleles of each parent separate and only one allele passes from each parent on to an offspring. Which allele in a parent's pair of alleles is inherited is a matter of chance. We now know that this segregation of alleles occurs during the process of sex cell formation (i.e., meiosis).
    According to the principle of independent assortment, different pairs of alleles are passed to offspring independently of each other. The result is that new combinations of genes present in neither parent are possible. For example, a pea plant's inheritance of the ability to produce purple flowers instead of white ones does not make it more likely that it will also inherit the ability to produce yellow pea seeds in contrast to green ones. Likewise, the principle of independent assortment explains why the human inheritance of a particular eye color does not increase or decrease the likelihood of having 6 fingers on each hand. Today, we know this is due to the fact that the genes for independently assorted traits are located on different chromosomes.

    These two principles of inheritance, along with the understanding of unit inheritance and dominance, were the beginnings of our modern science of genetics. However, Mendel did not realize that there are exceptions to these rules.

    NOTE: Some biologists refer to Mendel's "principles" as "laws".

    NOTE: One of the reasons that Mendel carried out his breeding experiments with pea plants was that he could observe inheritance patterns in up to two generations a year. Geneticists today usually carry out their breeding experiments with species that reproduce much more rapidly so that the amount of time and money required is significantly reduced. Fruit flies and bacteria are commonly used for this purpose now. Fruit flies reproduce in about 2 weeks from birth, while bacteria, such as E. coli found in our digestive systems, reproduce in only 3-5 hours.

    Source: http://anthro.palomar.edu/mendel/mendel_1.htm
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  2. #2
    Seedling organic in ottawa's Avatar

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    Default breeding bump

    A good crash course and THIS ONE HAS PICTURES!
    oio

  3. #3
    Shadbot 4.20 Shadimar's Avatar

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    In all seriousness, every time I go to the local asian buffet I think of Mendel.

    It's the smooth and wrinkled peas in the fried rice that sparks the memory
    ♪♫♪♫♪♪♫♪
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  4. #4
    Flowering Member brainpain's Avatar

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    Very nice!
    peace to who all read
    there will be a day when cannabis is accepted as a helpful drug. so that everyone may take advantage
    Brainpain

  5. #5
    Vegetative Member Rockster's Avatar

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    Gregor Mendel?

    I kiss his dirty gardening shoe and I love the boy! ( A bit of bastardised Shakespeare- Henry the 5th )

    What an incredible scientist that through meticulous observation of tens of thousands of plant populations came up with an explanation for how an F1 inbred generation exhibited great differentiation and all this has been fully born out by genetic science.

    The man was one of the greatest scientists of our times and to glean so much info from smooth or wrinkled pea's or purple or white flowers just blows me away in massive respect and awe.

    I'm just not fucking worthy!

  6. #6
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    Quote Originally Posted by Rockster View Post
    Gregor Mendel?

    I kiss his dirty gardening shoe and I love the boy! ( A bit of bastardised Shakespeare- Henry the 5th )

    What an incredible scientist that through meticulous observation of tens of thousands of plant populations came up with an explanation for how an F1 inbred generation exhibited great differentiation and all this has been fully born out by genetic science.

    The man was one of the greatest scientists of our times and to glean so much info from smooth or wrinkled pea's or purple or white flowers just blows me away in massive respect and awe.

    I'm just not fucking worthy!
    Let me be the first in text to observe and document a cyber "leg hump" by a bipedal mammal of a historical corpse. It's interesting, I feel your warmth bro and I think I need a shower. jk. It's either a leg hump or a near religious kneeling thing going on. But I get ya. Our modern genetics is fruit of Mende'\ls labour.

    Yeah it was scientific leap to be sure. I have to read this over because it's been years. Thanks for posting it Smoking Moose it's excellent.

    A guy was saying the other day, that when a cancer spreads, that it doesn't actually mutate into a 'new' cancer, which I didn't know. So if you have a breast cancer, apparently it doesn't travel through the body mutating into a brain cancer or a lung cancer. Similarly a blood born cancer doesn't mutate into colon cancer. We have to think in terms of literally millions and millions of computations (replications) to understand the unlikelihood of cancer happening (and the likelihood) - the likelihood IS extremely small, but you're running SO MANY computations (replications) that occasionally, maybe because of the influence of environmental risk factors impacting on the system during replication, like radiation, or radon, or benzene, or whatever, (an ''environmental precondition" say) a mutation 'happens'. So it was explained to me that with humans is, it happens with cell division, and genes are 'translocated' or the equivalent of their values being 'swapped' (I suppose like the photocopy metaphor) by the fact that the number of times replication has happened is huge over a lifespan (I would guess) - this translocation happens and so the swap makes a mutation. The mutations are often deleted by the immune system(e.g., mutated cells). But the growth rate of the cancerous mutations 'can' get away from the immune system if that immune system becomes compromised, for example. In healthy people the immune system handles it; the less healthy usually get nailed with it. So apparently too, if a cancer gets blood born, it can end up in the brain, but still be a colon cancer cell, as I understand it.

    Point is: Knowing the genetic processes has made understanding cancer something even we can do or approximate, thanks to his thinking skills and devotion to the cause. So yeah, when you're finished kneeling bro, move aside so I can bend one knee. It's also a good example of how having a good theory helps you understand the world.

    What gets me is: Each process is dirt stupid. Who would have thought it?
    Last edited by Rickkus; 02-20-2013 at 09:12 PM.

  7. #7
    Vegetative Member Rockster's Avatar

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    Dirt stupid indeed yet others would posit it's some complex algorithm written with the pens of angels.

  8. #8
    Vegetative Member

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    Quote Originally Posted by Rockster View Post
    Dirt stupid indeed yet others would posit it's some complex algorithm written with the pens of angels.
    Math is dope. I don't know anything about angels. But math is dope. I wish I really understood genetics. But I think you have to know chemistry for it, biology, ha. Not me . But I'm glad someone does and Mendel did.

    So Smoking Moose, how would you set up a breeding program if you wanted to breed for say, smell of k'ush, the most awesome of smoke? Or say a Jack Herer? What advice would you give noobs? Or anyone feel to chime in I would guess making a good cross with a Jack Herer male you'd want a good yielding and strong female indica with good potency (say 25%) so the smoke isn't something that makes you buzz off into Pixieland or turn paranoid and stupid from the sativa in Jack Male. Pure sativas are ok, once in a while, but I want to build a good hybrid 50:50 strain with some sweet citrus smell and yield. Insanely potent sativa or overconsumption paranoia I don't need, thanks.

    I've been building k'ush strains by crossing with other known and personally experienced k'ush that I've grown and smoked with a really reliable female clone k'ush I got from a dispensary. I don't have the numbers count to do it right, I don't think. But I'm quite happy with the k'ush with the crosses I've completed so far.
    Last edited by Rickkus; 02-20-2013 at 11:50 PM.

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    Shadbot 4.20 Shadimar's Avatar

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    I think of Mendel every time I go to any Asian buffet.

    It's the smooth and wrinkled peas in the fried rice that does it to me
    ♪♫♪♫♪♪♫♪
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