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#109816 - 06/11/13 03:52 PM Definitions(genetic load and others)
Wieslaw Offline
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Classroom Professor

Registered: 09/18/09
Posts: 3770
Loc: Denmark
I have been trying to find a good and simple definition of the term " genetic load". I have found several, of which the most simple said something like " the number of lethal genes carried by an average individual of the species".

The majority of other definitions were phrased in such a way, that I usually lost the meaning halfway to the end.

Examples:
1)
Genetic load is the reduction in selective value for a population compared to what the population would have if all individuals had the most favored genotype.[3] It is normally stated in terms of fitness as the reduction in the mean fitness for a population compared to the maximum fitness.


2)
Genetic load is a number between 0 and 1 and it measures the extent to which the average individual in a population is inferior to the best possible kind of individual. The genetic load equals the relative chance that an average individual will die before reproducing because of the deleterious genes that it possesses. Ignoring frequency-dependent selection, it is calculated as follows:

Suppose there are a variety of genotypes in the population, each with its characteristic fitness; one genotype has a higher fitness than the rest and we call its fitness Wopt. We can also measure the average fitness of the whole population; it is just the fitness of each genotype multiplied by its frequency: it is called mean fitness and is symbolised by v.


What is correct?

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#109823 - 06/11/13 10:18 PM Re: Definitions(genetic load and others) [Re: Wieslaw]
Canuck_Bock_RAT Offline
Chicken

Registered: 01/05/12
Posts: 104
Loc: Alberta, Canada
Heel low:

These three seem concise and to the point:


http://dictionary.reference.com/browse/genetic+load

Quote:
Genetic load
The extent to which a population deviates from the theoretically fittest genetic constitution.




http://en.wikipedia.org/wiki/Genetic_load

Quote:
Genetic load
In population genetics, genetic load or genetic burden is a measure of the cost of lost alleles due to selection (selectional load) or mutation (mutational load). It is a value in the range , where 0 represents no load. The concept was first formulated in 1937 by JBS Haldane, independently formulated, named and applied to humans in 1950 by H. J. Muller, and elaborated further by Haldane in 1957.




http://www.thefreedictionary.com/genetic+load

Quote:
Genetic Load
1. The relative difference between the theoretically most fit genotype within a population and the average genotype.
2. The aggregate of deleterious genes that are carried, mostly hidden, in the genome of a population and may be transmitted to descendants.


Hope one of the three works for you.

Doggone & Chicken UP,

Tara Lee Higgins
Higgins Rat Ranch Conservation Farm

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#109834 - 06/12/13 05:54 PM Re: Definitions(genetic load and others) [Re: Canuck_Bock_RAT]
Bushman Offline
Ruler of the Roost

Registered: 07/25/07
Posts: 1047
Loc: Wisconsin
What significance does the concept of genetic load hold to the average smallholder fancier, and how would he/she measure it?
_________________________
Pilgrim in a foreign land and true believer.
1st John 5:11-12

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#109837 - 06/12/13 06:52 PM Re: Definitions(genetic load and others) [Re: Canuck_Bock_RAT]
John Online   content
Chicken

Registered: 04/21/11
Posts: 78
Loc: Michigan
Quote:
Genetic load
In population genetics, genetic load or genetic burden is a measure of the cost of lost alleles due to selection (selectional load) or mutation (mutational load). It is a value in the range , where 0 represents no load.

So with chickens would the most pure (wildtype) Red Junglefowl be a "0"?
_________________________
John W Blehm
http://FowlStuff.com

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#109848 - 06/13/13 05:51 PM Re: Definitions(genetic load and others) [Re: John]
Wieslaw Offline
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Classroom Professor

Registered: 09/18/09
Posts: 3770
Loc: Denmark
I'd like to translate the notion of genetic load into Polish. There is an old thread where Ron Okimoto(?) mentioned that genetic load for people is 5 and for chickens is 6(or 4 and 5?). This is something I understand. But now I'm a little confused by those others definitions. How could I possibly use them in a sentence and on what purpose?

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#109878 - 06/17/13 12:39 PM Re: Definitions(genetic load and others) [Re: Wieslaw]
Canuck_Bock_RAT Offline
Chicken

Registered: 01/05/12
Posts: 104
Loc: Alberta, Canada
Heel low:

Originally Posted By: John
Quote:
Genetic load
In population genetics, genetic load or genetic burden is a measure of the cost of lost alleles due to selection (selectional load) or mutation (mutational load). It is a value in the range , where 0 represents no load.

So with chickens would the most pure (wildtype) Red Junglefowl be a "0"?


Careful John.

If we use this definition of genetic load (The extent to which a population deviates from the theoretically fittest genetic constitution) I propose that the Red Junglefowl (Gallus gallus) is not the fittest genetic example for my particular situation! Course we need another definition, which I will provide, "What is genetic fitness?"

http://dictionary.reference.com/browse/genetic+fitness

Quote:
Genetic fitness
The reproductive success of a genotype, usually measured as the number of offspring produced by an individual that survive to reproductive age relative to the average for the population.


A Red Junglefowl cannot always be zero because it would not be the best suited to my environment AND a survivor to replicate progeny (that live to replicate more of themselves) better than say my heavily mutated pseudo Red Junglefowl, the Chantecler! LMBO

I think with chickens, the "0" would be labeled on the most adapted (therefore it could also be the most "mutated" from wild type) individual with the most successful future; survival of the fittest. laugh

As Wieslaw says in his example provided, "measures the extent to which the average individual in a population is inferior to the best possible kind of individual."

The "best kind" of chicken for me is the Chantecler. I do keep ones that are not as fit, say the Booted Bantam with a single comb that may freeze and hurt, put a chicken off their game to replicate. So said, may I then use the "zero" rating for genetic load for the Chantecler and go forward from zero to a maximum of 1 to explain how UNfit the Booted Bantam is to my Chanteclers in my specific environment and my expected use for the chickens?

Course if I think about it, the Red Junglefowl could be a zero if raised in the jungle? Is this not then making your statement correct too? Nature knows best perhaps? Uh oh!

I am not positive, but I expect there are no perfect zeros for any chicken pending the circumstances of where the bird is, what purpose the bird is expected to be for, how it is raised, etc.

To each one of us, the "best possible kind of individual" is as variable as what the single word "good" means to each of us. Define a "good" bird and you'll have as many answers as there are those willing to respond.

I would expect genetic load of 0 is the best suited that survives to make more...chickeny perfection for each one of us. I would hate to tell you that your birds are nearer a one because they might not flourish in an Alberta blizzard! I think it key to know the boundaries of the "population" in question. My Province, your State; which continent North America, Europe. I guess I just simply get hung up over geography in regards to genetic fitness of a population! Even animal husbandry differences would come into play.

Who sets the criterion, who gets to say when the sample is closed within what parameters? Yes, largest number of offspring making more offspring is the deciding factor...but you can't sample the entire population ... or can you? <<wicked laughter>>

I suppose it depends on who is funding the $$research project$$...

Originally Posted By: Wieslaw
There is an old thread where Ron Okimoto(?) mentioned that genetic load for people is 5 and for chickens is 6(or 4 and 5?). This is something I understand.


I guess I don't understand. I am uncertain how Dr. Ron Okimoto is able to say 5 or 4 or 6 if what appears to be the traditional genetic load scale is measured from 0 to 1? How BAD are humans or chickens for that matter at level SIX...eep! Maybe 0 to 1 is not the correct definition for genetic load? Maybe 0 to 10 is the scale that he was using.

In that case, may I be a "negative 10" just to mess up any logical progression made here? :-p

Interesting topic.

Doggone & Chicken UP,

Tara Lee Higgins
Higgins Rat Ranch Conservation Farm

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#109879 - 06/17/13 01:32 PM Re: Definitions(genetic load and others) [Re: Wieslaw]
Canuck_Bock_RAT Offline
Chicken

Registered: 01/05/12
Posts: 104
Loc: Alberta, Canada
Heel low:

Originally Posted By: Wieslaw
But now I'm a little confused by those others definitions. How could I possibly use them in a sentence and on what purpose?


How about this...

Genetic load would measure the benefit of a male chicken having a Cushion comb wanting to replicate (fertilize females) in winter (therefore giving MORE opportunity to have more offspring) balanced by the negative measure of a pure Rose combed breed (lacking Pea comb) of male chicken and the number of offspring he would sire to survive to replicate offspring themselves. Since pure Rose comb has sperm that lives half the time of a non-pure or not Rose comb (Crawford & Smyth, 1964), the use of the measurement for genetic load would be able to account for the negative over pure Rose comb combined with the benefit of adding Pea comb to Rose comb to make a Cushion comb. The Cushion combed male would be "fitter" than a Single combed male with frostbite and be closer to zero than the Single combed male. Factoring in the pituitary gland requirement of over 14 hours of daylight for better fertilization by male chickens, of course. smile

A Single comb male nursing frostbite into April here, would by simple pain, not be interested in females and reproduction--he would lose his advantage over the Cushion combed male who's sperm lives half as long...put both males in a flock of females and the Cushion combed male would overcome his negatives to his good "genetic load" of having a pure Pea comb because someone bothered to select and add Rose comb to the genetic soup. He will breed and he will sire offspring while the Single combed male will be more concerned about his "head ache" than breeding females.

Is that a conversation you could have regarding "genetic load?"

"Cushion comb has less of a negative impact on genetic load than pure Rose comb by itself because the addition of Pea comb overcomes frostbite issues for reproductive interest in breeding males."

Doggone & Chicken UP,

Tara Lee Higgins
Higgins Rat Ranch Conservation Farm

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#109880 - 06/17/13 01:54 PM Re: Definitions(genetic load and others) [Re: Canuck_Bock_RAT]
SDWGame Offline
Bantam

Registered: 01/19/13
Posts: 59
Loc: Greenville, SC USA
Anyone who has raised a variety of chicken breeds including game fowl knows which breed of chicken has the highest survival potential. Some of the reasons are perfectly straightforward.

1. Bred for 6,000-8,000 years in which selection is based on the most athletic, aggresive and game is very similar to natural selection and insures reproduction of the fittest.
2. Often living outdoors with little or no shelter has increased hardiness, flying ability and inate predator avoidance skills.
3. Breeding crosses of unrelated individuals is the norm to achieve the benefit of heterosis (hybrid vigor)thereby increasing the genetic diversity of the individuals.

Say it ain't so and I'll convince you by introducing my 5 lb. rooster to your 9 lb. rooster.

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#109884 - 06/17/13 03:36 PM Re: Definitions(genetic load and others) [Re: SDWGame]
Wieslaw Offline
Moderator
Classroom Professor

Registered: 09/18/09
Posts: 3770
Loc: Denmark
I have actually found one of the threads

http://www.the-coop.org/forums/ubbthreads.php?ubb=showflat&Number=28843&Searchpage=1&Main=4086&Words=%22genetic+load%22&Search=true#Post28843

It was 2,5 for human and 6 for chickens

I will try to find the original(links do not work)

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#109885 - 06/17/13 07:21 PM Re: Definitions(genetic load and others) [Re: Wieslaw]
KazJaps Offline
Classroom Professor

Registered: 08/30/02
Posts: 2807
Loc: Australia
Probably R.Okimoto was using different scale to express the same thing (eg 0.5 = 50%)?

The Coop: CREATING A DARK EGGER

R. Okimoto:
The Coop: Inbreeding thread #2
Quote:
Inbreeding is the only way to purge detrimental alleles from a population. The less inbreeding that occurs in a species the higher the genetic load. This happens because recessives can build up in a population if they are never made homozygous. If you never inbreed, detrimentals can reach a higher frequency in your population. Chickens probably have a lower genetic load than quail because they have been domesticated in small local populations for 10,000 years and detrimentals have been slowly selected against.

Humans have a pretty low genetic load. It is estimated to be less than half what it is in chickens (around 2.5 instead of 6). Modern humans seem to have had a population bottle neck around 100,000 years ago where the world population may have dropped to only around 1000 effective individuals that can account for all the humans that we see today. Humans have about 1/5 the genetic variation that you find in chimps or just about any other species. It is sort of scarry, but back 100,000 years ago humans may have been just as endangered as most of the great apes are today.



The following from D. Caveny: The Coop:Bantamising a Breed
Quote:

When DeKalb started their inbreeding of fowl in the 1940's they used 25,000 pairs of bro x sis matings. 2 years later they had 250 pairs that were only 75% inbred. This illustrates how many undesireable traits had shown themselves and been eliminated.

Any time there is inbreeding individuals become more homozygous for traits and the bad ones effect viability or fitness to a great degree. My opinion is that inbreeding is a hocus that was championed early last century in an attempt to increase differences of lines prior to crossing in an attempt to maximize heterosis when the lines were crossed. Work in the last half of the 20th century illustrated that good nickability (and viability) could be had when lines were minimally inbred.


----------------------------------

So basically 'Genetic Load' is in reference to the accumulation of deleterious genes in a population.

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