# Inbreeding (Split from Are my mice pregnant or just fat?)



## kittygirl991 (Sep 16, 2011)

even so if inbreeding is good, by doing so the babies end up crippled or some faults


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## jadeguppy (Jun 4, 2011)

kittygirl991, you are posting assumptions as facts. If you have good genetics, then the babies will have good genetics. If you have bad genetics, yes you can end up with bubs that have faults. However, it is through careful inbreeding that those faults can be shown and eliminated. Top show breeders do this all the time to keep their top quality mice producing top quality.


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## SarahY (Nov 6, 2008)

> even so if inbreeding is good, by doing so the babies end up crippled or some faults


Wrong. Kittens do not end up deformed or cripples or faulty because of inbreding, they get that way because of bad genes. Inbreeding is an invaluable tool, it is outcrossing which is dangerous. Outcrossed animals have what is called 'hybrid vigour', which means they look healthy because they have only one copy of any nasty recessive genes. A breeder who continually outcrosses has no idea what his or her mice are carrying and those faults could be hiding there all along.

I inbreed my mice massively and outcross very, very rarely, and I have never, ever had a deformed kitten born. But if I did, it would highlight a problem in the line and I'd be able to do something about fixing it.


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## Mouse Queen 96 (Jul 11, 2011)

Inbreeding is 100% fine!  Like i said i just had mice born that were inbred. It make's their genes either stronger, or it will show their defaults so you know not to breed them again. It 100% make's their genes come through which could be benificial to you. So i would highly actually let people know that i do/did it. It in no way if your mice don't carry "bad" genes will harm your mice. They don't think of it as you mating with your father/brother/mother/sister, they forget. I had some of the most beautiful inbred mice, and all were sold to breeders because of quality.


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## kittygirl991 (Sep 16, 2011)

yeahh but its gross! would you have a child with your brother xD


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## maddeh (Jul 14, 2011)

If it was a choice between someone related that had no genetic problems or someone who was unrelated but had possible genes predisposing them to cancers,etc then actually, for the health and happiness of the baby, yes


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## SarahY (Nov 6, 2008)

> yeahh but its gross! would you have a child with your brother xD


Not a good attitude when it comes to mouse breeding I'm afraid  It's necessary, and it's only humans who have made it 'gross'. If humans were selectively bred to the extent that mice have been, it'd more than likely be perfectly safe for us to inbreed. We haven't though, which means all those nasty hidden recessives are lurking.



> If it was a choice between someone related that had no genetic problems or someone who was unrelated but had possible genes predisposing them to cancers,etc then actually, for the health and happiness of the baby, yes


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## jadeguppy (Jun 4, 2011)

kittygirl991 said:


> yeahh but its gross! would you have a child with your brother xD


This is a higly opinionated statement that has nothing to do with the health of the mice. As you have expressed a desire to breed mice, it is in their best interest that you look at it from a scientific aspect or not breed mice. There is nothing wrong with choosing not to breed. However, choosing to ignore best practices because it is gross will be to the determint of the mice. Inbreeding is the responsible thing to do to get a healthy line of mice with no hidden problems. It is one of the reasons that well bred mice rarely, if ever get some of the common tumors or other genetically influenced problems.


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## Laigaie (Mar 7, 2011)

The human disgust at the thought of inbreeding is a combination of cultural and biological issues. Since our culture need not influence our breeding practices, let's look at the biological. For humans, there are a lot of genetic disorders that are carried as recessive genes. That means that unless you're having children with someone else who carries it, your babies won't have those disorders. What's more, by mixing your genes with someone who's better than you at some things, say, who has perfect vision, is taller, and is more height-weight proportionate, improves the chances that your children will do well. 
With mice, however, we try to only breed the "best" mice, whether that's the typiest mouse or the prettiest mouse or the strongest mouse, or some combination of those factors (along with health). We're not necessarily concerned with breeding every single mouse, like humans are. We're concerned with breeding the best mice together. If the two best mice are related, all the better! That means that they will share a lot of the things that make them the best, which gives you the best chances for having mice at least as good as their parents, possibly better. If you're breeding for pets, inbreeding allows you to be certain that you're not passing along bad genes to your pet owners. If you're breeding for feeders, inbreeding allows you to build a better feeder breed mouse. If you're breeding for show, inbreeding is the only way to improve your line.


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## kittygirl991 (Sep 16, 2011)

so... should i breed for better genes? should i go back to the pet shop in which i bought maisie and millie and buy there brothers? cause then i would defiantly get a satin baby... but i havnt got enough houses to hold, the girls, the future babies and 2 seperate tanks for the boys


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## Laigaie (Mar 7, 2011)

If the brothers at the shop appear to be better than the male you have currently, possibly. If, however, you're unable to house additional bucks on a permanent basis, I'd advise working with what you have until such a time as those individuals can be replaced. If I remember correctly, you're not breeding for show or feeders, but for pets and for the experience of breeding. In that event, for your uses, you are probably better off with fewer mice rather than more. The purpose of the discussion on inbreeding, though, was to explain that it isn't necessarily a bad thing, and instead has quite a few uses.


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## jadeguppy (Jun 4, 2011)

If you don't have the tanks, don't breed them. If you cull you can eliminate extra males, but if you don't you can end up needing dozen more cages. If you want satin and your females are satin, you need a satin male. As you don't have a proven line, I'd pick the healthiest looking satin male in the color you want and start inbreeding at the second generation. Being from a pet store, you can't be sure who is related or what their genetics are. After the first litter you will hopefully have a better idea of what genes you are working with. You will basically be doing a test breeding to determine genetics and then carefully watch the mice grow to check for health, temperment, and type. It will also allow you to pick the best ones to breed back into the line. To get a line going, it is important to keep as many of the babes as you can to see if long term problems show up in a line. If they do, you need to stop breeding the line. Breeders will often have several lines from a family of mice going for a particular type (black, blue fox, etc.) until they are sure they have bred out all the problems possible.


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## tinyhartmouseries (Dec 30, 2010)

Don't breed if you don't have tanks. Even if you get enough for this generation, you'd just need more when you bred again.


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## moustress (Sep 25, 2009)

The issue of inbreeding mousies depends entirely on the quality of the line you are breeding to or from. I've been breeding for twelve years now. When I started, I tried not to inbreed, as I knew nothing about the genetics of the my pet store stock. After five or six years, I had weeded out most of the harmful recessives and felt it was okay to inbreed when I wanted to.

At the present time I rarely see any sort of deformity or chronic health problem that I would attribute to inbreeding. I now inbreed regularly, and my mousies are bigger, healthier, and more reproductively vigorous. Having good stock is the key, and for the breeders of show quality animals, inbreeding is not only OK, it's the key to producing nice big typey mousies.

On the other hand, if and when I notice a problem in a line of meeces, I will take a year or two to sort it out by use of culling, outcrosses, giving much consideration to the genetics in order to achieve my goal and eliminate that problem.


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## kittygirl991 (Sep 16, 2011)

oh ok thanks


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## Mouse Queen 96 (Jul 11, 2011)

kittygirl991 said:


> yeahh but its gross! would you have a child with your brother xD


In the old times even humans bred to their closest blood to keep their bloodlines pure. We are learning about it in History now. A couple hundreds of years ago, it didn't matter who was related. Alot of show breeders do it to keep their lines pure as well. If you have no bad lines, you won't have any problems.


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## SiamMeece (Sep 21, 2010)

In a lot of cultures it's still commonplace to marry within the family (though not brothers and sisters) usually for economical reasons (property stays within the family) I have a Turkish colleague who is married to a full cousin - just like his parents - and in the village he and his wife come from, about sixty procent of the people share the same last name.


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## tinyhartmouseries (Dec 30, 2010)

I have just heard someone state that lab mice suffer from inbreeding depression and they are very fragile because of this. This person stated that inbreeding generation after generation is SURE to cause inbreeding depression and create very sick mice, and there are scores of studies showing this. Does anyone have documentation of this?
I stand by the opinion that if you select for healthy mice and cull any mice showing ill health, no harm will come of it, only hardier mice.


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## SiamMeece (Sep 21, 2010)

All you need to know about inbreeding depression :idea: 
http://www.fancymice.info/inbred.htm


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## Laigaie (Mar 7, 2011)

And from there, the takeaway: " The depression in breeding will begin to fade away by the F8 generation with the elimination of all of the deleterious alleles. Inbreeding depression will not occur when a new inbred strain is begun with two parents who are themselves already inbred because no deleterious genes are present at the outset in this special case."


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## Roland (Aug 17, 2009)

SiamMeece said:


> All you need to know about inbreeding depression :idea:
> http://www.fancymice.info/inbred.htm


There is a little bit more to know:

INBREEDING - LINE BREEDING - OUTCROSSING

What is Inbreeding and what is it usefull for?

Inbreeding is the reproduction from mating of two genetically related parents.

Breeding in domestic animals is selective breeding primarily. Without the sorting of individuals by trait, a breed could not be established, nor could poor genetic material be removed.
Inbreeding is used by breeders of fancy mice to fix desirable genetic traits within a population or to attempt to remove deleterious traits by allowing them to manifest phenotypically from the genotypes. Inbreeding is defined as the use of close relations for breeding such as mother to son, father to daughter, brother to sister.

Systematic inbreeding and maintenance of inbred strains is of great importance for biomedical research. The inbreeding guarantees a consistent and uniform animal model for experimental purposes. Therefore many inbred mouse strains have been constructed, an example is the strain C57bl. Per definition a strain can be called inbred strain, after more than 20 generations of brother x sister matings. Many of the wellknown inbred strains go back to 1930, so they are stable strains now after more than 200 generations of brother x sister matings.

What is Inbreeding Depression ?

Inbreeding may on one hand result in more recessive deleterious traits manifesting themselves, because the genomes of pair-mates are more similar: recessive traits can only occur in offspring if present in both parents' genomes, and the more genetically similar the parents are, the more often recessive traits appear in their offspring. Consequently, the more closely related the breeding pair is, the more homozygous deleterious genes the offspring may have, resulting in very unfit individuals. For alleles that confer an advantage in the heterozygous and/or homozygous-dominant state, the fitness of the homozygous-recessive state may even be zero (meaning sterile or unviable offspring).
As a result, early generation inbred individuals are more likely to show physical and health defects, including:
•	Reduced fertility both in litter size and sperm viability
•	Increased genetic disorders 
•	Lower birth rates 
•	Higher infant mortality 
•	Slower growth 
•	Loss of immune system function

Another mechanism responsible for inbreeding depression is overdominance of heterozygous alleles. This can lead to reduced fitness of a population with many homozygous genotypes, even if they are not deleterious. Here, even the dominant alleles result in reduced fitness if present homozygously.

How could the laboratory inbred mouse strains develop nevertheless ?

Inbreeding depression is not a phenomenon that will inevitably occur. Given enough time and a sufficiently (but not too) small gene pool and a high number of individuals, deleterious alleles may be eliminated by natural selection by and by.
In a population where inbreeding occurs frequently, most offspring will have some deleterious traits, so few will be more fit for survival than the others. In populations with a large numbers of matings, the fittest will be selected and will survive. Breeders must cull unfit breeding suppressed individuals and/or individuals who demonstrate either homozygosity or heterozygosity for genetic based diseases. 
In laboratories the high number of animals allows the eradication of deleterious traits and selection of the fittest, while in smaller populations of private mouseries the inbreeding depression often results in a dead-end street, without a chance to move back.

What is hybrid vigour (Heterosis effect) ?

Heterosis, or hybrid vigor (or outbreeding enhancement), is the increased function of any biological quality in a hybrid offspring. It is the occurrence of a genetically superior offspring from mixing the genes of its parents.

Heterosis is the opposite of inbreeding depression, which occurs with increasing homozygosity. The term often causes controversy, particularly in terms of the selective breeding of mice, because it is sometimes believed that all crossbred mice are genetically superior to their parents; this is true only in certain circumstances: when a hybrid is seen to be superior to its parents, this is known as hybrid vigor. When the opposite happens, and a hybrid inherits traits from its parents that makes it unfit for survival, the result is referred to as outbreeding depression. 
Two competing hypotheses, not necessarily mutually exclusive, have been developed to explain hybrid vigor. The dominance hypothesis attributes the superiority of hybrids to the suppression of undesirable (deleterious) recessive alleles from one parent by dominant alleles from the other. It attributes the poor performance of inbred strains to the loss of genetic diversity, with the strains becoming purely homozygous deleterious alleles at many loci. The overdominance hypothesis states that some combinations of alleles (which can be obtained by crossing two inbred strains) are especially advantaggeous when paired in a heterozygous individual. The concept of heterozygote advantage/overdominance is not restricted to hybrid lineages. This hypothesis is commonly invoked to explain the persistence of many alleles which are harmful in homozygotes; in normal circumstances such harmful alleles would be removed from a population through the process of natural selection. Like the dominance hypotheses, it attributes the poor performance of inbred strains to a high percentage of these harmful recessives.

What is Outcrossing ?

Outcrossing is the practice of introducing unrelated genetic material into a breeding line. It increases genetic diversity, thus reducing the probability of all individuals being subject to disease or reducing genetic abnormalities by inbreeding depression. but it actually can serve to increase the number of individuals who carry a disease recessively, so has to be done carefully.
It is used in line-breeding to restore vigor or size and fertility to a breeding line. 
Outcrossing is now the norm of most purposeful breeding, contrary to what is commonly believed. The outcrossing breeder intends to remove unwanted traits by using "new blood" with better traits. With dominant traits, one can still see the expression of the traits and can remove unwanted traits whether one outcrosses, line breeds or inbreds. With recessives, outcrossing allows for the recessive traits to migrate across a population. It may actually increase the number of individuals carrying a disease. This technique of 'improving' fancy mice by outcrossing should therefore be persued with some caution and should never be applied to the entire stud until the full effects have been studied carefully. A great deal of selection has gone into the varieties now available and, of course, selection has been for different characteristics in different varieties. So whilst improving one aspect of the stock byan outcross may well bes setting other aspects back for many years.
However one may increase the variance of genes within the gene pool by outcrossing, protecting against extinction by a single stressor from the environment.
As we will see, a good mix of methods is linebreeding, which seems to be the best way to improve a bred and to combine the advantages of inbreeding and outcrossing: Line breeding

What is Linebreeding ?

Linebreeding is a form of inbreeding practiced by most successful breeders to "fix" desirable traits in a bred of animal, without as high a risk of producing undesirable traits that may occur with close inbreeding.

The Inbreeding Coefficient makes the difference between inbreeding and line breeding. The coefficient of kinship is defined as the probability that the alleles at a particular locus chosen at random from two individuals are identical. In the mouse, the coefficient of relationship between parent and offspring is 50%, meaning half of the offspring's genome comes from that parent. Half the genes are identical by descent. The inbreeding coefficient of pairing parents x offspring is 25%. The inbreeding coefficient is roughly half the relationship coefficient.
Line breeding differs from inbreeding by the pairings, which are allowed. 
In linebreeding it is not allowed to breed for inbreeding coefficients higher than 12.5%. This method is even helpfull to establish recessive traits. The homocygous offspring showing the recessive trait has to be selected.

Not allowed for linebreeding:
•	parent x offspring 25%
•	full siblings x full siblings 25%

Allowed for linebreeding:
•	grandparent X grandchild 12.5%
•	half siblings x half siblings 12.5%
•	first cousins x first cousins 6.25%
•	great grandparent x great grandchild 6.25%
•	second cousins x second cousins 3,125%

Linebreeding fixes desirable traits and allowes the introduction of superior traits. Therefor this is the best method to improve the quality of lines in a mousery.

What has to be done if you want to use line breeding for your mousery ?

Linebreeding in private mouseries consists of setting up two or three lines per variety from a common initial stock. Each line operates separately from the others and the objective is to try to select for improved features whilst as far as possible avoiding common parents. Once the lines are well established, since they all have been derived from a common initial family or a single buck, they can be used as outcrosses for one another - when it seems necessary - thereafter returning to the former system of line breeding and selection. If you like, line breeding is rather less severe than inbreeding. One mates members of the same line or strain rather than near relations of a family group. 
Start withn two not clesly related very good bucks and several very good but not closely related does. From the offspring start backcrosses as described under line breeding above.
A very occasional cross outside the strain may be used to correct or improve particular features or weaknesses, but this should be done carefully and selectively. Wholesale outcrossing which newcomers sometimes resort to, ususally results in a considerable deterioration in the medium to long term.

Regards, Roland
Chilloutarea Mousery - Tricolor , Splashed , Merle , Recessive Red


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