severe inbreeding does not decrease variation

interesting real population

Hope this works better than it seems to do on preview.

The article worked fine for me.
Interesting - but the first thing I'm wondering is if you could really go from 2 to 700 sheep in 20 years?

2 to tenth is over 1,000...so there has been plenty attrition.

I have been waiting for this to be posted on the sheep board...for the "guru" to expound upon

Let us first and foremost assume that this kind of sheep has one lamb at the time.
Then assume some are lost along the way. The flock needs only to grow by some 34,1% per year.
Bear in mind that half of this growth will be rams. 100 ewes will need to give birth to 34 surviving lambs, or roughly one lamb in three years per ewe.
I would call this type of growth possible, giving room for many to lamb their first in their second or even third year.

outsidethebox wrote:

2 to tenth  is over 1,000...so there has been plenty attrition.

I have been waiting for this to be posted on the sheep board...for the "guru" to expound upon  

Would be a total waste of effort as any mountainside climb up to the perch of the sheep guru(s). That site is full of gurus as are many "advanced" or "advantaged" animal sites. They can clearly see the peaks where little occurs but wind and storms but during all the while the real of life and true breeding is below the clouds. Their concern is how they buy animals, bought the wrong animals, paid too much, talk up animals, market animals, link animals, depend on outcrossed individual animals or breeds, isolate others from their animals, or talk individual plans while honestly either following the crowd, reverting to regionalism or retreating to isolation and irrelevance. Hurrah to Megan and others who defend their turf with actions and words in the business of producing food and fiber. There are too many wimps, snipers, irrational non-thinkers and apologist in the ag industry anymore.

I find studies like this to be interesting in that a highly inbred population can thrive, maintain high fertility and defy what we would call the "odds". It enthuses me to keep breeding tight on lines and to let the animals and lines cull themselves or select themselves. But I am fully aware that without human selection this isolated population would most likely have low economic value to most commercial operations. There's give and take to all.

Feel free to run it up the flagpole if you care to.

The weakness' resulting from the levels of inbreeding in theory and mindset from groupthink , dwarf any reality of what happens genetically.

Grassfarmer wrote:

The article worked fine for me.
Interesting - but the first thing I'm wondering is if you could really go from 2 to 700 sheep in 20 years?

surely not without any records or pedigrees

a longer read...

http://www.mysteriousbritain.co.uk/england/staffordshire/folklore/chartley-white-park-herd.html

EddieM wrote:

outsidethebox wrote:

2 to tenth  is over 1,000...so there has been plenty attrition.

I have been waiting for this to be posted on the sheep board...for the "guru" to expound upon  

Would be a total waste of effort as any mountainside climb up to the perch of the sheep guru(s).  That site is full of gurus as are many "advanced" or "advantaged" animal sites.  They can clearly see the peaks where little occurs but wind and storms but during all the while the real of life and true breeding is below the clouds.  Their concern is how they buy animals, bought the wrong animals, paid too much, talk up animals, market animals, link animals, depend on outcrossed individual animals or breeds, isolate others from their animals, or talk individual plans while honestly either following the crowd, reverting to regionalism or retreating to isolation and irrelevance.  Hurrah to Megan   and others who defend their turf with actions and words in the business of producing food and fiber.  There are too many wimps, snipers, irrational non-thinkers and apologist in the ag industry anymore.

I find studies like this to be interesting in that a highly inbred population can thrive, maintain high fertility and defy what we would call the "odds".  It enthuses me to keep breeding tight on lines and to let the animals and lines cull themselves or select themselves.  But I am fully aware that without human selection this isolated population would most likely have low economic value to most commercial operations.  There's give and take to all.

Feel free to run it up the flagpole if you care to.

Oh no, I am not about to take on that group...though there would be significant entertainment value in it.

From my simpleton view nature resorts to many different way to restore "enough" variation.

Simple logic would tell me inbreeding has to reduce variation in the genotype (although the title implies otherwise), not so much maybe the phenotype... at least of what I have seen here.

But in this case if I refer to Larry's mating systems chart, this supposed "severe" inbreeding only occurred I assume when forage was in abundance providing extra nutrition to the possibly regressed and small in numbers population.

As the population would grow in numbers it would move away from the left side of the chart and move toward centre no longer "severe" inbreeding and of course as the numbers increase even more, variation increases and nature takes care of that with a shortage of food to cull the extremes and keep the population in the middle.

I know here the tightly bred cattle need more inputs to survive and multiply then the general population does.

Here is the real story:


http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1766376/

The theory that inbreeding causes weakness in a population does not work if nature culls weak individuals, thereby lessen the frequency of bad alleles. So there are not much left of the "bad" genes (the lethal and deleterious genes)
after a number of years.
Second thing due to the heterosis effect, certain rams have an advantage both when it comes to fighting for ewes and for fertility, thus leaving more and more genetically diverse progeny than more homozygous rams do. In this way the odd alleles are conserved, simply because the more unusual an allele becomes, the more it tends to help its bearers in form of heterosis, and the more common it becomes again.
The same phenomenon of course in the ewes, the more heterozygous, the more survival and reproduction.
So from time to time there are numbers of more inbred individuals, they just leave less progeny than the less inbred do.

Clearly, a population will suffer more from genetic drift if it is small than if it is big, this population is not small enough.

A couple of interesting things in that info tulip. The numbers didn't rise exponentially from 1957-1977 they were increasing very slowly for the first 10 years - was there a genetic reason for the slower population growth at this time? Where numbers really took off around 1972.

"Haute Island is rocky with a weak grass cover (only 30% of the island) and, in 1972, fodder grass was introduced to increase the foraging resources of the island."

Coincidence? Maybe not relevant to the genetic variation topic but it sure looks like it may have something to do with the population explosion.

tulip wrote:

Here is the real story:


http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1766376/

Thanks,

That gives a little more perspective, defiantly over my head but basic just seems to be what you'd expect.

This tidbit made me smile  

"However, longitudinal genetic data of natural populations are very scarce. Furthermore, migration or population demography may interfere with drift making genetic changes in natural populations difficult to predict."

Hilly wrote:

tulip wrote:

Here is the real story:


http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1766376/

Thanks,

That gives a little more perspective, defiantly over my head but basic just seems to be what you'd expect.

This tidbit made me smile  

"However, longitudinal genetic data of natural populations are very scarce. Furthermore, migration or population demography may interfere with drift making genetic changes in natural populations difficult to predict."

it was Tyler moment for me

http://www.ted.com/talks/tyler_dewitt_hey_science_teachers_make_it_fun/transcript?language=en

edited to add Kendra`s comment about the above link for any skimmers reading

This might get a little annoying and sappy, enjoyed the message though as I think it has a lot of relevance in pointing out the disconnect between teaching and learning as well as the myth that complicated language must be used to prove the credibility and validity of the information