Genetics have always been an interest of mine. Various genes display and express various traits and outcomes. I decided to create a blog post for those of you who may not be especially genetically savvy when it comes to Punnet Squares and the color outcomes in rabbits. These PDFs that I am including in this post are primarily for Silver Fox (and SF/NZ crosses) that I breed because they only cover the base, dilute, and broken genes. I’ve also included a How To Use file, see below.
To start, let’s talk vocab. You need to know some basic words if you’re going to even begin trying to understand genetics, regardless of species and traits.
– Allele – a variation or form of a gene (ie. B and b); there are 2 copies of an allele per genetic trait or genotype (ie. BB, bb, or Bb) since genes work in pairs
– Dominant – the primary expressed gene, often expressed by a capital letter (ex. B vs b where B is the dominant trait)
– Recessive – the secondary expressed gene, often expressed by a lower case letter (ex. B vs b where b is the recessive trait)
– Homozygous – two copies of the same alleles, can either be dominant or recessive homozygous (ie. BB or bb)
– Heterogyzous – two copies of different alleles (ie. Bb) – it is a general rule that heterozygous animals will produce the largest amount of genetic variation in offspring
– Genotype – the genetic constituents of an organism, or the genetic code
– Phenotype – the traits expressed by the genetic code (aka what you see)
Now, more specific traits pertaining to Silver Fox and New Zealand rabbits.
– Base color: expressed either B or b; B is dominant, b is recessive; BB or Bb displays the color black, while bb displays the color chocolate. An animal that is heterozygous for base color is said to be “black carrying chocolate” (Bb). BB is homozygous dominant base. bb is homozygous recessive base. Chocolate and black are the two base colors.
– Dilute color: expressed either D or d; D is dominant, d is recessive; DD or Dd displays no dilution; while dd displays dilution of the base color. DD is homozygous dominant dilution (no dilution), Dd is heterozygous dilution (carries but does not display dilution), and dd is homozygous recessive dilution (displays dilution of the base color). Dilution of black is blue. Dilution of chocolate is lilac.
– Broken pattern: expressed either En or en (ignore double letters, it really could be just E and e); En is dominant, en recessive. enen is a self animal that displays no broken pattern, aka solid color (homozygous recessive); Enen is a broken animal that displays the “ideal” pattern/amount of white (heterozygous), and EnEn is a charlie animal that displays minimal pattern and max white (homozygous dominant). Broken genes work somewhat differently as they display with only one copy of the dominant gene, and with two copies they display a “maxed pattern” of the gene.
– I have not included the REW gene in this overview as I don’t breed for it, and it is simply a masking gene that does not affect underlying color. REW acts like a blanket and is expressed when two animals who carry OR express REW are mated, producing a REW. The basis for this is an unaffected animal (rewrew), carrier (REWrew), and expressing animal (REWREW). It works similarly to the dilute gene, animals can carry it but may not express it.
Dilute and base genes work in tandem with one another. The dilute gene is a modifier of the base coat. I breed for the four colors that are modified via base and dilute genes – black, chocolate, blue, and lilac. I also cross in broken New Zealands so the pattern gene (which does NOT affect base or dilute color) is also at work in some animals.
To begin, you need to understand how to use a Punnet Square. See my How To Use file. A Punnet Square is simply a fairly easy way to call out an animal’s genotype and figure out what phenotype(s) will be expressed when bred to an animal of another genotype. It’s a great tool to use to predict what colors you’ll get from a breeding, and can also help you decipher what genotype your rabbit (or other animal) may be.
For black animals, there are four possible genotypes: BBDD (homozygous black); BbDD (black carrying chocolate); BBDd (black carrying blue); and BbDd (heterozygous black carrying both chocolate & blue). An animal is said to be a “carrier” of a phenotype (color) if they carry one copy of the gene that expresses said color (ie. b for chocolate, d for blue) but does NOT display that color. I have listed out the possible color combination outcomes for black animals below:
For blue AND chocolate animals, there are two possible genotypes for each color: BBdd (homozygous blue); Bbdd (blue carrying chocolate); bbDD (homozygous chocolate); bbDd (chocolate carrying blue). I have listed out the outcomes for blue and chocolate color combinations below (and see above black combinations for outcomes with black animals):
For lilac animals, there is only one possible genotype: bbdd. That is because lilac is a double, homozygous recessive trait. bb for chocolate and dd which is expression of dilution, in this case diluting chocolate, which expresses lilac. All lilac outcomes are listed in files above, and when a lilac is bred to a lilac, they will ALWAYS produce 100% lilacs.
For broken animals, the genotypes and their expressions were listed above. Broken genetics are simple, and can easily be guessed. Regardless, I have included Pattern Breeding Outcomes in my PDFs so you can see visually. Double pattern (EnEn) will always produce patterned offspring (either brokens or charlies).
Hope this hasn’t been too confusing. I keep these PDFs for personal use so I don’t have to do Punnet calculations every time I breed a new animal. It also helps me determine parent genotypes via offspring phenotypes (ie. if I breed my black doe to my lilac buck and only have black offspring [in a sizeable litter of 5+], I know that doe is homozygous black BBDD based on the Punnet for that cross). I will make some blog posts in the future regarding other colors – thinking about reds, etc. that can also be seen in NZs. Don’t ask me about a lot of the mods such as otter, etc. Once you understand Punnets, however, you should be able to create and calculate your own breeding outcomes just fine 🙂