February 12, 2023
by Robyn Paterson
The Bengal cat falls into a category of cat breeds known as hybrids, but this label is not scientifically accurate. The confusion this creates can be problematic for the so-called hybrid breeds. Breeds labeled hybrids are, essentially, backcrossed breeds. What is backcrossing? How is it different from hybridizing? Why is the difference significant for the Bengal cat?
Hybridizing versus Backcrossing - What is the difference?
Hybridizing is when two different types of animals (species or breeds) are bred together. Hybridizing aims to combine the desirable characteristics of both types into a single offspring. The F1 Bengal is a hybrid; one parent is a leopard cat, and one parent is a domestic cat - often, but not always - a Bengal. To continue a line of hybrids, both genders must be fertile. F2 hybrids come from two F1 hybrids breeding together. This is not possible with the F1 Bengal hybrids.
The male F1 hybrid between a leopard cat and a domestic cat is not fertile. Therefore, two F1 Bengals cannot be hybridized to make F2s. Thus, F2 and F3 Bengals cannot be created. Backcrossed Bengal males remain sterile until the fourth generation. Even then, fertility can be unreliable at the fourth and fifth generations when too much leopard cat DNA has passed down. Therefore, female F1 Bengal hybrids are backcrossed to fertile domestic Bengal males.
Backcrossing is when an individual from a hybrid population is bred back to one of the original parent types (species or breed). Backcrossing aims to transfer specific traits from the leopard cat to the Bengal population while retaining the desirable characteristics of the Bengal cat. The first cross between a leopard cat and a Bengal is a hybrid; however, every generation after that is a backcross.
F1 females are backcrossed to a domestic Bengal cat to create the second generation. This generation is scientifically called N1 or BC1. However, this terminology can cause confusion within the Bengal breeding world because N1 or BC1 could easily be confused with F1 creating a misunderstanding of how many generations the cat is removed from the wild species. To keep the generations from the wild species clear, Bengal breeders started using G as an abbreviation for generation. Instead of calling the second generation an N1 or BC1, we call them a 2G for second-generation backcross. 3G stands for the third-generation backcross. At four generations away from the leopard cat, over 50% of both genders are fertile. This is considered the true start of the Stud Book Traditional (SBT) Bengal breed.
The distinction between hybridizing and backcrossing is important for the Bengal cat. When hybridizing, one is maintaining equal parts of both species. When backcrossing, the leopard cat genetics reduce, and the domestic Bengal cat genetics increase with every generation. The goal of the Bengal breed is to create a domestic cat with the appearance of the leopard cat, but the personality of the domestic cat.
How much leopard cat DNA does a Bengal have?
Through Chris Kaelin's recently released research study, we have learned more about the limited number of genes that the leopard cat passes down to the Bengal. The leopard cat's genes are not evenly spread through Bengal DNA. Furthermore, they had passed down at a lower rate than expected, suggesting that there may have been times when only certain types of leopard cat genes were selected to be passed down. Researchers studied the genes of 722 Bengal cats and found that only a few of their genetic regions showed signs of leopard cat DNA. Problems with incompatible genes appear to have limited how much leopard cat ancestry Bengal cats have.
It isn't easy to bring a new leopard cat line down to SBT Bengal. For example, we have one 2G female who did not produce her first litter until she was seven years old. Not every breeder has the patience to work with cats who do not breed quickly; thus, some hybrids never contribute to Bengal cat genetics. This creates a situation where only some leopard cats' genes get passed on, leading to some genetic bottlenecks.
After the F1 generation, some leopard cat genes simply do not pass down. In the study of 722 SBT cats, researchers learned 7% of the Bengal cat genome does not have any leopard cat genes in any of the SBT Bengals. The leopard cat DNA ranged from .4% to 16% in SBT Bengals. The average Bengal cat has less than 3% leopard cat DNA.
Why is all of this important?
As regulations on wildcats spread worldwide, the Bengal cat must be recognized for what it is - a domestic cat. At times the Bengal cat is misrepresented as the genetic equivalent of a liger or coydog because they are called a hybrid breed. Bengals are NOT a hybrid breed. The breed begins with an F1 Hybrid, but after three successive generations of backcrossing to domestic Bengals cats, the offspring are genetically domestic cats. It is important that breeders, owners, and legislators all recognize the Bengal as the domestic cat that it is.
Kaelin, Christopher B., et al. "Ancestry dynamics and trait selection in a designer cat breed." bioRxiv, Cold Spring Harbor Laboratory, 12 December 2022, https://www.biorxiv.org/content/10.1101/2022.12.12.520105v1.full.pdf. Accessed 12 February 2023.
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