genetic theory

J

jay

Well-Known Member
20+ year member
Is there someone who is an expert, or at least very knowledgable on genetics on this forum?
My knowledge is a bit rusty.

If in breeding programs the idea is to retain as much of the genetic diversity as possible (the figure is I think around 90-95%), then how id this assured. If an animal has one young then they are only going to pass on half of their genetic inheritance. Having two young won't help as they may pass on a similar lot of genes as in their first young. The more young they have the better as it is more likely that they will pass on the majority og genes that they have. Yet this is impossible as this would overfill zoos with just one bloodline. What is the ideal number of young which will give the most likely chance of acheiving the most genetic divirsity?
 
jay said:
Is there someone who is an expert, or at least very knowledgable on genetics on this forum?
My knowledge is a bit rusty.

If in breeding programs the idea is to retain as much of the genetic diversity as possible (the figure is I think around 90-95%), then how id this assured. If an animal has one young then they are only going to pass on half of their genetic inheritance. Having two young won't help as they may pass on a similar lot of genes as in their first young. The more young they have the better as it is more likely that they will pass on the majority og genes that they have. Yet this is impossible as this would overfill zoos with just one bloodline. What is the ideal number of young which will give the most likely chance of acheiving the most genetic divirsity?
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Hi Jay,

The minimum recommended starting number for a population like this is 20 pairs of unrelated animals. Hence the need for lots of spaces being available before a breeding prograim is considered. And conversely, lack of this number of founding animals is one of the reasons for reviewing if it is worth even starting a population, or phasing out small populations of related animals, when further recruitment of unrelated animals is highly unlikely.
 
And how many young would each individual animals have to have to pass on the max. amount of their genes without having too many?
 
The general number for a population to be viable is 500. of course this would depend on a lot of factors. It has been a while since I did genetics and conservation biology so there may be some refinement since then. But really, you would need to have maximum genetic diversity in founders or you will get genetic drift and the population will be less viable if the genes left are not good for a sudden change in environment.
 
jay said:
If in breeding programs the idea is to retain as much of the genetic diversity as possible (the figure is I think around 90-95%), then how id this assured.
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There is theoretical estimate, how big variability is. How many animals over how many generations lose how much variability. It depends from population size, generation time and mating system.

Sadly AFAIK they don't take into account real genetic variability. E.g. all animals in breeding programme might come from one wild subpopulation which was not representative for whole species.

jay said:
If an animal has one young then they are only going to pass on half of their genetic inheritance. Having two young won't help as they may pass on a similar lot of genes as in their first young. The more young they have the better as it is more likely that they will pass on the majority og genes that they have. Yet this is impossible as this would overfill zoos with just one bloodline.
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But you have relatively many animals and few gene alleles to pass on.

jay said:
What is the ideal number of young which will give the most likely chance of acheiving the most genetic divirsity?
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If you have stable population - two. In practice, few zoo populations are stable - you have new founders coming, overbred and underbred animals etc. In tiger plan, in was once hoped that underrepresented founder should leave five young, and overrepresened - one.
 
jay said:
And how many young would each individual animals have to have to pass on the max. amount of their genes without having too many?
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It depends on the amount of space available in zoos and the strength (over-populaton) of the animal's genetics. In the US, recommended population sizes average about 200 individuals. (There are only 218 AZA facilities, and not all of them are zoos)

But is important to note that population managers dont necessarily know the answer to this question until that animal's offspring have all reached sexual maturity and are breeding. Especially with genetically important individuals, you dont want to minimize their offspring in the event some were to die. Also, in order to maximize the potential of one's genes, it would be important to breed (or have offspring) with as many different partners as possible to create the most genetic diversity.

I would also think that since each individual animal is genetically distinct, that every individual should breed at least once. However, this can be nearly impossible in well established populations due to space constraints.

To answer your question, I would have to say that an animal should produce the maximum amount of offspring to truly allow population managers to maximize that indiviual's genetics.
 
It's strange how some species seem to thrive with only a small founder base.
Aren't all the hamsters in the world descended from just one female? And aren't the world's cheetahs virtually identical genetically, suggesting a genetic "bottleneck" occurred somewhere in their evolution?

Himalayan Tahrs and Barbary Sheep (Aoudads) in Australian zoos are going along merrily in terms of successful breeding generation after generation despite having very few founders. (They are listed for phase-out, but nobody's told them!)
 
Ara said:
It's strange how some species seem to thrive with only a small founder base.
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Small founder base is random - may lead to establishing genetic disorders and extinction, but may also lead to purging genetic disorders.

There are natural examples of animals which got second scenario, e.g. european beavers and badgers.

BTW - can anybody confirm if all Laysan Ducks descend from one clutch of last female, so for short time population size was 1?
 
Ara said:
Himalayan Tahrs and Barbary Sheep (Aoudads) in Australian zoos are going along merrily in terms of successful breeding generation after generation despite having very few founders. (They are listed for phase-out, but nobody's told them!)
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what will they put on the mountain at Taronga if they phase out Tahrs?
 
Are there any examples of captive breeding programs that have followed the book with recommended number of unrelated founders. I'm know that most of the famous ones, Pere davids deer, arabian oryx, californian condor etc, also sumatran tiger were not started in favourable conditions. What about the Ne-Ne?
 
I did read once all Arabian Oryx were bred from nine animals brought togeather from a handful of zoos which was then named the "world herd"
 
Jurek7 said:
BTW - can anybody confirm if all Laysan Ducks descend from one clutch of last female, so for short time population size was 1?
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That is supposedly the story.... I'm not sure if its really true however, or whether other ducks were found still living there at a later date..

Pinta Island(Galapogos) Tortoise still has a population of one(lonesome George) unless they can ever find him a mate.
 
MARK said:
I did read once all Arabian Oryx were bred from nine animals brought togeather from a handful of zoos which was then named the "world herd"
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That's correct although I'm not sure it was as many as nine(?) The 'World Herd' was established at Phoenix Zoo Arizona (which has similar climatic conditions to Arabia) and I think the founder animals were donated by an Arab Shiek- plus one female 'Caroline' from London Zoo(their only Arabian Oryx at that time) Not sure if the Sheik retained some-I think he may have done so...

Because of its extreme rarity, the Arabian Oryx was treated almost like a 'fabled' animal then- a far cry from nowadays with several thousand captive bred animals awaiting release and London Zoo's small herd now banished to some stalls and a hardstanding at Whipsnade..:(
 
jay said:
What about the Ne-Ne?
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NeNe were struggling in the wild when a private rancher called Shipman established a small captive flock (circa 1940/50's). He later sent a pair to Slimbridge UK- these were in fact two females so a male(named Kamehameha) was then sent over to join them. Slimbridge's flock are descended from that trio though I'm sure they've had several infusions of new blood since. Although Slimbridge are popularly associated with saving the species, the Hawaian rancher, Mr Shipman, was really the initial mover in this effort.

I don't think NeNe became extinct in the wild- just very low numbers.
 
Yer I know I have the figures here filed away some where but I am real sure it was only nine of them in the herd.

The founders for all the Przewalskis horses in zoos today were only 11 animals, not that many really
 
i read that there was two lineages of mongolian horses, one pure, one slightly hybridised with domestic blood, but still appearing true to the wild type?

lab mice are disgustingly inbred on purpose - it better to compare virtually genetic clones when doing experiments.

i read that cheetah were so inbred that they were essentially almost all as related as siblings, even twins! which always made me wonder? why do zoos even bother attempting to maintain genetic diversity - if its true then there is none!!

yes, some animals thrive despite low founders and rapidly rediversify. apparently the fact that just a single pair of brushtail rock wallabies founded the wild hawaiian population has done little to affect them. they apparently are quite genetically healthy and already adapting both physically and behaviourally into their own species.
 
the cheetah is an interetsing one, a thousand or so yrs ago people came in and killed a heap, and disease and everything- basically just a really bad trot for the old cheetah.

that left maybe 200 animals or something random, then they inbreed so much, they now are all really related- AND due to this males have low sperm count, and low fertility due to what sperm is created is very low quality- hence low successful pregnenceys and births in our programs.

I to heard they are closely related as twins, though i guess eventually they will be able to diverge somewhat. well untill they come out will 10 eyes and 8 legs (wow tht will be afst) then i guess we should keep trying to breed them
 
Another species that has a low founder population is - wait for it - humans!
Apperently in one ice age the number of humans alive on the planet at one time got down to as few as a couple of thousand. Despite the fact that physically we are very diverse, it is a shallow divirsity. Our gene level divirsity is very low. Source New Scientist though I haven't a clue what issue.
 
jay said:
Another species that has a low founder population is - wait for it - humans!
Apperently in one ice age the number of humans alive on the planet at one time got down to as few as a couple of thousand. Despite the fact that physically we are very diverse, it is a shallow divirsity. Our gene level divirsity is very low. Source New Scientist though I haven't a clue what issue.
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Wouldnt that explain a large number of the people on the forum :D!
 
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