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A basic guide to tortoise genetics for Breeders


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#1 Guest_MichaelDevonUK_*

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Posted 23 March 2006 - 04:07 PM

A basic guide to genetics for Tortoise breeders.

By Michael Babb 2006.


I have written this article for those individuals interested in breeding tortoises.

Most tortoises captive in the UK resulted from wild caught specimens taken before the trade ban in the1980s.

We have an ageing population of tortoises and we wonít be able to replace them when they are gone!

Many of the tortoise species kept in the UK are generally very scarce or even very rare in their native homelands.

In my opinion propagation, breeding of these tortoises is vitally important and plays an active role in the conservation of species.

Sharing our breeding experiences both positive and negative can only improve our overall understanding of tortoises and in turn allowing us all to gain a greater understanding of their ecology and requirements.


So where do I start?

This is where we all start a Male and a female from different sources and probably no guarantee of exact origin, when I say that they may have been imported before the trade ban from Algeria but then of course they could be Algerian Testudo Graeca Graeca or possibly Furculachelys Whitei (Gilbert Whites Tortoise) also found in Algeria.

Even greater regional variation occur in Moroccan specimens carapace markings are varied according to the race, part of Morocco the individuals are found.

Well firstly find tortoises of the correct species e.g. Testudo Graeca Ibera (Turkish Spur-thighed Tortoise).

Itís no good having a Hermans Tortoise (Testudo Hermanni Hermanni) and then attempting to breed it to a (Testudo Graeca Ibera).

Breeding from different species is only doomed to failure as often males might refuse to mate with their partner and if they did successfully sterile offspring may be produced or the offspring resembling no other tortoise on the earth!

Letís look quickly at the definition of a Pure Breed as defined by pedigree animal breeders all around the world.

They use a basic knowledge of genetics to produce offspring of standard size, colour, etc.

Pure breed Basically means that if two individuals are mated together all the potential offspring will resemble both their mother and Father in appearance and characteristics such as size shape etc.

So we need to match our tortoises well to produce offspring of good type and to ensure they inherit the general characteristics of their parents.

It is very easy to add genes but very difficult to take them out!

Predictable breeding can only be achieved if an individual ancestry past is known when I say that I mean you could take a female ibera for example and she could well look like any other ibera but was actually produced from a father of a different species. The Ibera genes were expressed dominantly and she looks like an ibera but in fact she is a hybrid and carrying genes which are not characteristical of the species.


Another breeder buys her and attempts to produce his own offspring he or she is shocked when the hatchlings look very unlike their mothers a bit like no other tortoise on earth.

My examples are hypothetical just to give you an idea of what I mean.

Genes can be carried and donít always express themselves but do have a habit of showing up further down the line often generations later.

Hybrids are created when two different species are mated together. The resultant progeny then being classed as ĎHybridsí.

It is very important to manage our existing tortoises within the UK to keep these breeds pure and not to produce a generation of hybrids.


Future serious breeding would produce unreliable and unpredictable genetical inheritance.

If youíre in any doubt about your tortoises species join a group such as the Tortoise Trust or (BCG) British Chelonia Group.

Both of these groups have experts only too willing to help with identification of your tortoises.

Finding a compatible pair of tortoises can often be difficult. The Classification of tortoises and the sub-species debate is still going strong to this very day.

Try your best ask the experts and listen to them thatís my advice.

Identification can be difficult as I have found out during the last year with my Testudo Graeca Graeca!

I have a group of Testudo Graeca Graeca but their origin extends from Algeria through Morocco and into Libya.

Males of species prefer to mate with individuals resembling that of their individual race carapace markings, base colour etc.

The Genetics transferred from this type of mating will usually guarantee hybrid vigour, strength but also produces individuals of a more unpredictable type, natural variation.


Offspring could all look like one of the parents a mixture looking like both or have the same coloured skin for instance of the Female but the head shape of the Male.

There are no predictable results from outcrosses and some strange looking hybrids may result so I advise leaving well alone!


This mating would rarely form in the wild as tortoises are quite sedentary and form distinct populations and races.


There is much regional variation in Testudo Graeca Graeca found in Libya for example. All exhibit basic features of the Holotype but carapace markings can vary considerably.


In-Breeding.

This type of breeding involves mating individuals who are often distantly related. Although populations may interbreed the population size combined with some genetical variation allow the population to thrive and maintain strength.

This mating between individuals probably occurs readily in the wild where a small population size is present.

Selective in-breeding is carried out by pedigree breeders of animals all around the world with the goal of achieving a specific type look and predictable offspring being produced.

The disadvantage of this system lies in its ability to breed in Faults as well as improve the species.

Selection is paramount to success and individuals should have experience of breeding before attempting in breeding.

In general terms half of individuals genetical make up is inherited from the Mother and half from the father.


(A) Mother 50 % + (B) Father 50% = Offspring F1 50% A / 50%B


When for instance a Son for example is then mated back to their Mother the resulting offspring would achieve greater inheritance from the Female side of the mating.

(A) Mother + (Z) Son F1 = Offspring F2 = 75% (A) + 25% (Z)



The mother in this mating has a greater genetical influence in the resulting offspring 75% of the genetics inherited from the mother.

This genetical influence could be greater still if the F2 offspring shown above were again back crossed to the Mother (A).

This can be explained as a form of In-Breeding but I would not advice this if out crossing alternative described earlier can be achieved.

Another term commonly used by animal breeders for this mating would be Ďpairing down the lineí.

Considerable skill is required in mating specimens of good type and as said before you could possibly increase the incidence of bad faults e.g. deformities etc.

Mating Brother and Sisters together also restricts the possibility of diverse genetical diversity as the genes will be the same from both sides of the Brother and sisterís inheritance, genetical make-up.

This is a more extreme system of In-Breeding and in my opinion only attempted as a last resort.

Better to practice out crossing and pairing down the line wherever possible to achieve the greatest genetical diversity and variation.

I must add here that inbreeding can succeed for many generations if faults are identified and culled from breeding!


But on the downside faults deformities weakness can easily express themselves and form a dominant part of a tortoiseís genetical makeup.

Itís easier to put genes in than take them out again!

But I would stress that wherever possible try to select stock from similar geographical origin and likeness. If your tortoise pair look alike they are more likely to share a common genetical ancestry.

Finally genes express themselves by means of both Dominant and recessive factors. The combination of these factors will determine particular factors being expressed in resultant offspring.


Blue eye colour in humans is the result of a recessive gene in action.

In conclusion it is of paramount importance to breed from Captive bred stock in a logical way and mate, pair individuals from the same species and geographical regions.

These distinct races have evolved over thousands of years so letís all try to breed from compatible pairs wherever possible and aim for maintaining as wide a genetical diversity as is possible, whilst maintaining individuals offspring true to type e.g. Race.

It is left to us all as individuals to breed and maintain tortoises of similar genetical likeness, many of these tortoises are now very rare in their native homelands.

Once a tortoise becomes extinct their genes also become extinct and are lost to us all forever!


Michael Babb 2006 (Copyright).



#2 Guest_shootinglou79_*

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Posted 23 March 2006 - 04:22 PM

mikey this is superb hun, welldone, keep up the good work ;-)



linzi-lou

1.1.0. hermanns
0.1.2. spur thighs(ibera)
linzi-lou

1.1.0. hermanns
0.1.2. spur thighs(ibera)


#3 Guest_Darren_*

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Posted 23 March 2006 - 04:48 PM

mike am at work and read the first few lines only, fantastic i will print it out and read it later, and you are spot on with keeping the species going it great work, i am slowly building my collection of graeca's but no females yet !!!! URRRGGGGGGHHHHHHHHHH


#4 Guest_vale46_1_*

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Posted 23 March 2006 - 08:28 PM

Well said Mike.

Steve


#5 Guest_Calamity Jane_*

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Posted 23 March 2006 - 08:35 PM

Nice one!!
Good Info. ;)

Yours
Calamity Jane :*
www.tortoises.piczo.com
www.Testudo-hermanni-boettgeri.piczo.com
My Tortoises :D
2.3.2 Hermanns


#6 Guest_p1glet_*

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Posted 24 March 2006 - 09:49 AM

Hi Mike
Thats an exellent script i for support you and the TT-BCG 100% in all the work you do to keep true species lines true to type great one ,hope i to can contribute to the captive breeding programme for graeca spp in captivity with my my baby graeca , thanks also for all you help
Darren


#7 Guest_blondesarah_*

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Posted 24 March 2006 - 10:36 AM

Very well written, well done!


#8 Guest_simo_*

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Posted 24 March 2006 - 11:33 AM

Very interesting!!!





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