Genetics and Supermodels

What do Kate Moss and recessives have in common? More than you think

By Denise Flaim
RRCUS Health and Genetics Chair

Successful breeding – whether you’re talking about rutabagas or Ridgebacks – requires an understanding of genetics.

Yet despite all the seminars and the books and the magazine articles, it’s astonishing that a good many people in dogs still don’t quite understand the basics of how dominant and recessive genes work.

Admittedly, the subject as it is taught in biology class isn’t exactly sexy. Genotypes, heterozygosity, alleles … See? I’m losing you already.

In this age of “Joe Millionaire” and “American Idol,” perhaps the standard template to explain the basics of genetics – the story of 19^th-century Augustinian monk Gregor Mendel and his pollination experiments with pea plants – doesn’t cut it anymore. Perhaps these theories would be better understood in a popular-culture context ... say, using supermodels.

There are two kinds of genes – dominant and recessive. But for our purposes, let’s call them Anna Nicole Smith genes and Kate Moss genes, respectively. (And when we think of Anna Nicole, let’s think of her in her reality-TV stage, before she became a Trimspa spokesperson and lost her, er, zaftig silhouette.)

Genes always come in pairs. So let’s imagine our two genes walk in a dressing room, and let’s assume that Annas and Kates can exist in multiples. If that’s the case, we can have three possible combinations: two Anna Nicoles, two Kate Mosses, or one of each.

In genetics, that’s called a “genotype”: The actual genes an organism has.

Imagine now that our supermodel genes need to get ready for the runway. There’s only one mirror in the dressing room, and the two fight for position to apply their MAC lipstick. If you look in the mirror as they jostle, what you see will depend on who your two supermodels are. If you have two Anna Nicoles, you’ll see at least one of those busty blondes in the reflection. If you have two Kate Mosses, the image in the mirror will be stick-thin, even if you only see one. When the two genes are the same like this, whether they’re both Annas or both Kates, that’s called “homozygous.”

But if you have one Kate Moss and one Anna Nicole – what the geneticists call “heterozygous” -- that’s a little more tricky. While Kate Moss is present, you wouldn’t know it. Looking in the mirror, all you see is bigger-than-life Anna, even though Kate is struggling right behind her.

This reflection is what is called “phenotype” – it’s what you see of the genes expressed in the actual animal.

Dominant genes do what our imaginary Anna has done to Kate – they block them. But just because you don’t see Kate in the mirror doesn’t mean she isn’t in the dressing room.

During reproduction, each parent contributes one of his or her genes to the new life being formed. In other words, one of the models in your dressing room goes to your offspring. Which model? That’s the unpredictable part.

What does all this have to do with dogs? In Ridgebacks, we know black noses are dominant and liver noses are recessive. So substitute “black nose” for Anna Nicole and “liver nose” for Kate Moss.

Let’s say a sire has two Anna Nicoles. In other words, he’s a dominant black nose. Let’s say he’s bred to a livernose bitch – in supermodel speak, that means she has two Kate Mosses. Their offspring will each inherit an Anna from him and a Kate from their mother. Because, following our metaphor, Anna hogs the mirror, they’ll all be born blacknoses. But they each carry a Kate, which means they can produce livernoses if bred to the right dog.

Here’s a more complicated scenario: You are breeding two dogs who are heterozygous for nose color. (That is, they each have one Anna and one Kate.) To figure out what the probability of their offspring’s nose color will be, you have to draw a Punnett square. Put the sire’s genes on the top of the box, and the mother’s along the side. Then, take the gene from each column and row, and place them in the corresponding box, like so:

Click on the picture above to view a larger image

The results? With any given puppy, there is a 25 percent chance he will be homozygous blacknose (two Annas), a 25 percent chance he will be livernose (two Kates) and a 50 percent chance he will be blacknose but carry the recessive gene for liver (one Anna and one Kate).

That’s all very nice, you think, but how does this help me with my breeding program? Well, substitute a genetic condition or conformation fault that is known to be linked to a simple recessive gene, and you have your answer.

Our supermodel scenario also helps to show how genes technically aren’t “diluted” by outcrossing. That is, a gene itself isn’t changed or weakened by outcrossing, anymore than you can shove Anna Nicole and Kate Moss into a dressing room and hope Naomi Campbell walks out instead. Annas still stay Annas, and Kates still stay Kates. While outcrossing might reduce the chances of two Kates walking out of your dressing room – and so preventing a trait from being expressed -- it can also help “hide” a trait, as that elusive Kate hides behind normal, dominant Annas, sometimes for generations.

Only by figuring out who’s a carrier – that is, whether there’s a Kate lurking behind Anna in that proverbial dressing room – can you hope to eliminate or breed out an undesirable trait.

In the end, drawing Punnett squares and guessing at genetic outcomes isn’t a guarantee, because genetics is based on probabilities. But then again, so is Las Vegas, and when it comes to the big picture, the casinos win more than they lose. For a breeder, understanding the risks of a potential genetic can provide more consistent results than just groping in the dark. And on a breed-club level, a focus on genetics will hopefully lead to the ultimate breakthroughs for our most nagging genetic problems: DNA tests that can conclusively identify where the Kates are hiding, and how to avoid them.

© Denise Flaim 2004

This article originally appeared in The Ridgeback Register