brother/sister mating

Question
what happen if a brother and sister rabbit mate together

Answer
Dear Jason,

Well, for one thing, they could produce babies.  And that's not a great thing for all the reasons here:

www.bio.miami.edu/hare/breeding.html

But it is also not good for the babies.  I don't know how much background you have in genetics, so here's a short primer.  Genes, as you probably know, are the units of inheritance that control our physical appearance and how our bodies run.  Most recent estimates suggest that a typical mammal has about 30,000 genes,

Every animal (including rabbits and humans) carries two copies of every gene: one inherited from mom, and one inherited from dad.  The two copies of a particular gene may not be exactly identical to each other.  This is why animals are so physically and functionally variable.  Different versions of the same gene are called *alleles*.  An individual may have two of the same allele of any particular gene, or may have two different versions (alleles) of that gene.  What does this mean?

A brief example.  There is a human gene that codes for the shape of the forehead hairline.  There are two versions of the gene.  One, which we'll call "W", codes for a small "V" of hair to point down onto the forehead (Widow's Peak--the Dracula hairline!).  The other version, which we'll call "w", codes for a straight hairline.  In this gene, the W allele (Widow's peak) of the gene will *mask* the expression of the w allele (Straight hairline) if a person has one of each allele.  Thus, the W allele is said to be *dominant*, and the w allele is said to be *recessive*.  So if every person has two copies of this gene, then the possible combinations are:

WW - Widow's peak (Two dominant alleles:  the individual is homozygous dominant)
Ww - Widow's peak (One of each allele:  the individual is heterozygous)
ww - straight hairline (Two recessive alleles:  the individual is homozygous recessive)

Some traits are more complicated than hairline in humans, and may be controlled by *several* different interacting genes, each with two or more versions (alleles).  This means that the different versions can combine and interact in unpredictable ways to produce a wide range of phenotypes (physical appearance).

Different versions of genes are the result of mutations:  changes in the genes from one generation to the next.  And sometimes these changes can be harmful.  In most cases, harmful mutations produce recessive alleles, and they will not be expressed (i.e., show up in the phenotype) unless the animal has two copies.  In that case, the harmful trait will show up.  Sometimes such traits are so harmful that they are lethal, and the animal cannot survive.

In a brother/sister mating, there is a greater chance that the babies will inherit two copies of the same harmful, recessive alleles because siblings have a greater chance of sharing such alleles, even if they are not expressing them (because they are heterozygous).  In rabbits, there are several known harmful mutations, including that which produces dwarf rabbits.  If two *dwarf* rabbits mate, an average of 25% of their offspring will be homozygous for a lethal gene that causes them to be doomed "peanuts."

Even if your brother/sister rabbits are not dwarf rabbits, they may still have harmful alleles that will have a high chance of being expressed in their offspring.  So please have both bunnies spayed/neutered and allow them to live happy lives together in bonded joy.  Please read:

www.bio.miami.edu/hare/spay.html

and find a good rabbit vet here who can help you through this process:

www.rabbit.org/vets

I hope this helps.

Dana