| The Basics of Inheritance |
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The value of studying genetics is in understanding how we can predict the likelihood of inheriting particular traits and help us to produce rabbits with desirable qualities. Genes are inherited equally in pairs - one from each parent for each trait. Breeding systems: Inbreeding - A system of breeding using very closely related rabbits such as dam to offspring. Line Breeding - A less intensive form of inbreeding using rabbits that are distantly related to each other. Outcrossing - Mating unrelated stock of the same breed. Cross Breeding - Mating rabbits of different breeds. (Sometimes referred to as “hybrids”). Benefits of inbreeding: Producing rabbits with consistent, desirable traits. Choosing rabbits with desired characteristics increases the chances of producing offspring with those same desired traits. The diverse breeds we have today were created by selecting individuals with unique traits and using them in a breeding program. Drawbacks of inbreeding: Inbreeding Depression (lowered vitality, less resistance to disease, smaller litter size, more chance of inheriting congenital disorders). Simple mode of inheritance - Dominant & Recessive Genes Dominant: Masks the effects of recessive genes. Recessive: Gene masked by the effect of a dominant gene. Must be inherited by both parents in order for it to be expressed. Dominant genes are written in capital letters “B“; recessive in lower case “b“. Genotype: The inherited genes of a rabbit. Phenotype: The physical appearance of a rabbit. Homozygous: inheriting the same gene for a trait from each parent Heterozygous: inheriting a different gene for the same trait from each parent. An example of Dominant inheritance - English Spotting Gene “En” The broken gene only needs to be inherited from one parent for the gene to express itself. Two self rabbits bred together can never produce a broken. (But do remember that a ruby eyed white may be hiding the broken gene!) Broken x Self = 50% broken; 50% self Broken x Broken = 50% broken, 25% self; 25% charlie Broken x Charlie = 50% broken, 50% Charlie Charlie x Self = 100% broken An example of Dominant inheritance - Dwarfing Gene DW - The gene need only be inherited from one parent for the offspring to show the trait. When 2 dwarfs are bred together, 25% of the litter will inherit the dwarfing gene from each parent. This homozygous form of dwarfism is fatal (Dwarfing gene inherited from both parents). Dwarf Buck: DW dw bred to Dwarf Doe: DW dw Offspring: 25% normal size (BUD or BUB) dw dw - 50% desired dwarf size DW dw - 25% lethal homozygous dwarf (peanuts) DW DW An example of Recessive Inheritance (Albinism cc) - The gene must be inherited from both parents to show the trait: If 2 black rabbits "C" are bred together which each carry the albino "c" gene, 25% of the litter will be black, 50% will be blacks that carry the recessive albino gene and 25% of the litter will be albino. Cc x Cc = CC Cc Cc cc How genes determine the sex of a rabbit: Male XY Female XX Offspring will be 50% male & 50% female: XX XX XY XY Genes can also be inherited in other complex modes that may combine effects or effect how other genes are expressed. Some genes may also be expressed or controlled depending on the sex of the rabbit. F1 (filial) generation - The first generation resulting from the cross of two unrelated lines or breeds. Subsequent inbreeding produces each new generation subsequently numbered: F2, F3, F4, etc. Rabbits are generally considered to be “purebred” by the 3rd filial generation when an entire 3 generation pedigree can be filled out. This term is frequently used by Lionhead breeders. Tips for success! Set goals for herd improvement. Avoid “barn blindness” by having a friend help to evaluate your herd. Breeding only the healthiest rabbits can help to produce a strain resistant to many diseases and parasites! Using a top quality buck will have the fastest impact on your herd. Good sanitation, excellent ventilation, fresh feed and water will enhance the quality of your herd. |