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Intro To Plant Genetics Definitions


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#1 BloodShotI'z

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Posted 13 November 2007 - 11:24 PM

Info provided by: Greg Green's Cannabis Breeder's Bible

Genes - Genes are the units of heredity transmitted from parent to offspring, usually as part of a chromosone. Genes usually control or determine a single characteristic in the offspring. There are genes responsible for each feature of your plant. Including leaf color, stem structure, smell, potency etc.

Gene Pairs - All life is mad up of a pattern of genes. Similar to the two sides to a zipper. One side (gene) is inhereted from the mother and the other side (gene) is inherited from the father. Each gene occupies a specific locus on the chain (zipper) and controls information about the eventual characteristic of the plant. Each gene locus contains two genes, one from each parent.
These gene pairs are denoted by a pair of letters (ex. BB, Bb, bb).
Any letter can be applied to any gene pair. "B" can represent "Big Buds" while "b" can represent "small buds" in this instance.

Chromosone - A thread like structure of nucleic acids and proteins in the cell nuclei of higher organisms that carries a set of linked genes, usuall paired.

Locus or loci - A position on a chromosone where a particular gene pair is located.

Allele - Allels are any number of alternative forms of one gene. For ex. the gene for purple bud color may have two forms, or alleles, one for purple and another for dark red.

Homozygous - Having identical alleles at one or more genetic loci, which is not a heterozygote and breeds true. Your plant is said to be homozygous for one feature when it carries the same gene twice in the responsible gene pair, which means both genes of the gene pair are identical (ex. BB)

Heterozygous - Having different alleles at one or more genetic loci. Your plant is said to be heterozygous for one feature when the genes of the responsible gene pair is unequal or dissimilar (ex. Bb)

Phenotype - The summary of all features you can detect or recognize from the outside of your plant. Ex. Color, smell, taste etc.

Genotype - The genetic constitution of your plant as distinguished from the phenotype. The genotype charachterizes how your plant looks from the inside. It is the summary of all genetic information that your plant carries and passes on to its offspring.

Dominant - Dominant is used to describe a gene or allele that is expressed even when inherited from only one parent. It is also used to describe a hereditary trait controlled by a gene and appearing in an individual to the exclusion of its counterpart, when allels for both are present. Only one dominant allele in the gen pair must be present to become the expressed genotype and eventually the expressed phenotype of your plant.

Recessive - Recessive describes a gene, allele or hereditary trait expressed only in homozygotes, being masked in heterozygotes by a dominant allele or trait. A gene is called recessive when its effect can not be seen in the phenotype of your plant when only one allele is present. The same allele must be present twice in the gene pair in order for you to see it expressed in the phenotype of your plant if it's a recessive trait.

Dominant/Recessive genetic notation - Assume that the dominant "B" allele carries the hereditary trait for Big Bud. While the recessive "b" allele carries the hereditary trait for small bud. Since "B" is dominant, a plant with the Bb genotype will always produce Big Bud. The "B" is dominant over the "b". In order for a recessive gene to be displayed in the phenotype, both genes in the gene pair must be recessive. So a plant with "BB or Bb gene will always produce Big Bud. Only a plant with "bb" genes will produce small bud.

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#2 BloodShotI'z

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Posted 13 November 2007 - 11:35 PM

When breeding cannabis. One must not only identify phenotypes but they also need to know if the genes responsible for what they see or smell are:

Homozygous Dominant - BB = Big Bud
Heterozygous - Bb = Big Bud
Homozygous Recessive - bb = Small Bud.

The Big/Small buds are phenotypes. The BB, Bb and bb denote the genotypes. Because "B" is the dominant allele, A plant with a"Bb" genotype will produce Big Buds not small buds.

Most phenotypes are visual characteristics but some like taste, are phenotypes that cant be observed by simply looking at the plant.
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#3 blakeb

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Posted 14 November 2007 - 03:59 PM

welcome to bio 101 lol

#4 SHAMAN

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Posted 14 November 2007 - 09:34 PM

very cool!!!

#5 BloodShotI'z

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Posted 14 November 2007 - 10:30 PM

Asking the question: If purple bud color is a dominant trait, why do some of the offspring of my purple bud strain have green buds?

or

I have been selecting Indica mothers and cross-breeding them with Mostly Indica male plants...but I have some Sativa leaves...why?

The 1st question reflects a common misconception: The dominant allele will always have the highest frequency. Thats not always the case. A dominant trait will not always spread to the entire population....Nor will a recessive trait always die out.

Gene frquencies can occur in high or low ratios regarless of how the allele is expressed. The allele can also change depending on certain conditions. Changes in gene frquencies over time result in different plant characteristics.

continued.....
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#6 BloodShotI'z

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Posted 14 November 2007 - 10:38 PM

A genetic population is basically a group of individuals of the same species (Cannabis Indica, Sativa or Ruderalis) or strain (Skunk #1 or Masterkush) in a given area whose members can breed with one another.

This means that they must share a common group of genes. This common group of genes is known as the gene pool. The gene pool contains the alleles for all the traits in the entire population. For a step in evolution-a new plant species, strain or trait to occur, some of the gene frequencies must change.

The gene frequency of an allele refers to the number of times an allele for a particular trait occurs compared to the total number of alleles for that trait in the population. Gene frequency is calculated by dividing the number of a specific type of allele by the total nunmber of alleles in the gene pool.

#7 BloodShotI'z

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Posted 14 November 2007 - 10:48 PM

The Hardy-Weinberg Model of genetic equilibrium describes a theoretical situation in which there is no change in the gene pool. At equilibrium there can be no change or evolution.

Consider a population whose gene pool contains the alleles for "B" and "b".

Assign the letter "p" to the frequency of the dominant allele "B" and the letter "q" to the frequency of the recessive allele "b".

We know that the sum of the alleles must equal 100% so:

p + q = 100% or p + q = 1

And all the random possible combinations of the members of a population would equal:

p2 + 2pq + q2

p = frequency of the dominant allele in the population
q = frequency of the recessive allele in a population
p2 = percentage of homozygous dominant individuals
q2 = percentage of heterozygous recessive individuals
2pq = percentage of heterozygous individuals

continued...
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#8 BloodShotI'z

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Posted 14 November 2007 - 11:12 PM

Imagine that you've grown a population of 1,000 Black Domina plants from seeds obtained from a well known bank. In that population, 360 plants emit a skunky smell, while the remaining 640 plants emit a fruity smell.

You contact the breeder to ask which smell is dominant in this strain. Hypothetically, they tell you that they selected for a fruity smell and the skunk smell is a recessive genotype. Lets call this recessive genotype "vv" and use the formula above to answer the following questions:

Q: According to the Hardy-Weinberg law, what is the frequency of the "vv" genotype?

A: Since 360 out of the 1,000 plants have the "vv" genotype, then 36% is the frquency of "vv" in this population of Black Domina.

Q: According to the Hardy-Weinberg law, what is the frequency of the "v" allele?

A: The frequency of the "vv" allele is 36%. Since q2 is the percentage of homozygous recessive individuals, and q is the frequency of the recessive allele in a population, the following must also be true:

q2 = 0.36
(q x q) = 0.36
q = 0.6

Thus, the frequency of the "v" or recessive allele is 60%.

Deduction will also tell you that the frequency of the "V" or domainant allele is 40%.

Q: What is the frequency of the genotypes "VV" and "Vv"?

A: Given what we know the following must be true:

VV = p2
V = 0.4 = p
(p x p) = p2
(0.4 x 0.4) = p2
0.16 = p2
VV = 0.16

The frequency of the genotype "VV" is 16%

VV = 0.16
vv = 0.36
VV + Vv + vv = 1
0.16 + Vv + 0.36 = 1
0.52 + Vv = 1
Vv = 1 - 0.52
Vv = 0.48 or 48%

So 48% of the population carry the heterozygous allele (Vv).

Or alternately, "Vv" is 2pq, therefore:

Vv = 2pq
2pq = 2 x p x q
2pq = 2 x 0.4 x 0.6
2pq = 0.48 or again....48%

The frequencies of "V" and "v" (p and q) will remain unchanged generation after generation as long as the following five statements are true:

1. The population is large enough
2. There are no mutations
3. There are no preferances, for example "VV" male does not prefer a "vv" female by its nature.
4. No other outside population exchanges genes with this population.
5. Natural selection does not favor any specific gene.

The equation p2 + 2pq + q2 can be used to claculate different frequencies. Although the equation is important to know about, we make use of other more basic calculations when breeding. The important thing to note here is the five conditions for equilibrium.

Early we asked the question:

"I have been selecting Indica mothers and cross breeding them with mostly Indica male plants...But I have some Sativa leaves...Why?"

The Hardy-Weinberg equilibrium tells us that outside genetics may have been introduced into the breeding program. Since the mostly Indica male plants are only MOSTLY Indica and not pure Indica, you can expect to discover some Sativa charactheristics in the offspring. Including the Sativa leaf trait.
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#9 Guest_HighPhi_*

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Posted 15 November 2007 - 03:09 PM

shit man are you some kind of scientist hehehe,

#10 BloodShotI'z

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Posted 15 November 2007 - 03:57 PM

Some may ask the question:

"How do I know if a trait such as bud color is homozygous dominant (BB), heterozygous (Bb) or homozygous recessive (bb)?"

If you've been given seeds or a clone you may have been told that a trait such as potencyis homozygous dominant, heterozygous or homozygous recessive. However you will want to discover this for yourself, especially if you intend to use thoise specific traits in a future breeding plan. To do this, you will need to perform what is called a test cross.

Determining phenotype of a plant is fairly straightforward. You look at the plant and you see, smell, feel or taste its phenotype. Determining the genotype cannot be achieved through simple observation alone.

continued.....

#11 BloodShotI'z

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Posted 15 November 2007 - 04:06 PM

Generally speaking, there are three possible genotypes for each plant trait. For example if Golden Bud is dominant and Silver Bud is recessive, the possible genotypes are:

Homozygous Dominant: BB = Golden Bud
Heterozygous: Bb = Golden Bud
Homozygous Recessive: bb = Silver Bud

The Gold and Silver bud colors are phenotypes. BB, Bb and bb denote the genotypes. Because B is the dominant allele, Bb would appear Golden and not Silver. Most phenotypes are visual characteristics but some, like bud taste are phenotypes that cant be observed by the naked eye and are experienced through other senses.

For example, looking at a Mostly Sativa species like a Skunk plant you will notice that the leaves are pale green. In a population of these Skunk plants you may notice that a few have dark green leaves. This suggests that this Skunk strain's leaf color is not true breeding, meaning the leaf trait must be heterozygous because the homozygous dominant and homozygous recessive traits are true breeding. Some of the Skunk's pale green leaf traits will probably be homozygous dominant in this population.

#12 BloodShotI'z

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Posted 15 November 2007 - 04:31 PM

You may also be asking: "Could the pale green trait be the homozygous recessive trait and the dark green leaf the heterozygous trait?"

Since a completely homozygous recessive population (bb) would not contain the allele for (:banghead: for heterozygous expression (Bb) or for homozygous dominant (BB), it is impossible for the traits heterozygous (Bb) or homozygous dominant (BB) to exist in a population that is completely homozygous recessive (bb) for that trait.

If a population is completely homozygous for that trait (BB or bb), then that specific trait can be considered stable, true breeding or 'will breed true'. If a population is heterozygous (Bb) for that trait then that specific trait can be considered unstable, not true breeding or 'will not breed true'.

If the trait for BB or BB cannot exist in a bb population for that trait, then bb is the only trait that you will discover in that population. Hence, bb is true breeding. If there is a variation in the trait, and the Hardy-Weinberg law of equilibrium has not been broken, the trait must be heterozygous. In our Skunk example there were only a few dark green leaves. this means that the dark green leaves are heterozygous and may possibly be homozygous dominant too.

You also notice that the bud is golden on most of the plants. This also suggests that the Golden Bud color is a dominant trait. If buds only on a few of the plants are Silver, this suggests that the Silver trait is recessive. You know the only genotype that produces the recessive trait is homozygous recessive (bb). So if a plant displays a recessive trait in its phenotype, its genotype must be homozygous recessive (bb). A plant that displays a recessive trait in its phenotype ALWAYS has a homozygous recessive genotype.

But this leaves you with an additional question to answer as well: Are the Golden Bud or pale leaf color traits homozygous dominant (BB) or heterozygous (Bb)? You cannot be completely certain of any of your inferences until you have completed a test cross.

A test cross is performed by breeding a plant with an unknown dominant genotype (BB or Bb) with a plant that is homozygous recessive (bb) for the same trait.

This brings us to an important rule: If any offspring from a test cross display the recessive trait, the genotype of the parent with the dominant trait Must be heterozygous (Bb) and not homozygous (BB or bb).

#13 BloodShotI'z

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Posted 15 November 2007 - 04:52 PM

In our example, our unknown genotype is either BB or Bb. The Silver Bud genotype is bb. We'll put this information known as Punnett squares.

b b
B
?
We start by entering the known genotypes. We do these calculations for two parents that will breed. We know our recessive trait is bb and the other is either BB or Bb, so we'll use B? for the time being. Our next step is to fill the box in with what we can calculate.

b b

B Bb Bb

? ?b ?b

The first row of offspring Bb & Bb will have the dominant trait of Golden Bud. The second row can either contain Bb or bb offspring. This will either lead to offspring that will produce more Golden Bud (Bb) or Silver Bud (bb). The first possible outcome (where ? = :banghead: would give us Golden Bud (Bb) offspring. The second possible outcome (where ? = :banghead: would give us Silver Bud (bb) offspring. We also can predict what the frequency will be.

Outcome 1, where ? = B:
Bb + Bb + Bb + Bb = 4Bb
100% Golden Bud

Outcome 2, where ? = b:
Bb + Bb + bb + bb = 2Bb + 2bb
50% Golden and 50% Silver Bud

Recall:

Homozygous Dominant: BB = Golden Bud
Heterozygous: Bb = Golden Bud (due to dominant allele :scream:
Homozygous Recessive: bb = Silver Bud.

To determine the identity of B?, we used another cannabis plant of the opposite sex that was homozygous recessive (bb) for the same trait.

Outcome 2 tells us that:

*Both parents must have at least one b trait each to exhibit Silver Bud in the phenotype of the offspring.

*If any Silver Bud is produced in the offspring then the mystery parent (B?) must be hetrozygous (Bb). It cannot be homozygous dominant (BB).

Figure the rest out for yourselves.
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#14 GreenWeaver

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Posted 19 February 2014 - 08:26 PM

MUTATION!.....once in a unpredictable time you will get the "ONE".  


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#15 KnuckleDragger

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Posted 20 February 2014 - 01:50 PM

Genetics really isn't terribly hard, it's just really complex. If your really interested, this is the book to read.

I wish some of the so-called breeders would read it.


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#16 AstheCROWflies

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Posted 21 February 2014 - 12:52 PM

Thanks again KD and Bloodshotl'z, great info.



#17 1mojavegreen

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Posted 22 February 2014 - 02:17 PM

hell yeah, this thread rocks!

rasta.nana.gif

kudos knuckle & blood!

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