Genetics for the Poodle Lover’s Soul (Part I)

Author: Katherine Bryce, CPDT, CMG
               The Family Dog
               Santa Fe NM USA

Please see the Glossary at the end of this article to find definitions. Also, I’ve done a fair bit of research for this article and included my sources at the end. Don’t be shy! Learn new words and find out what’s going on in a very interesting field!

First, let me make it clear that I am NOT a geneticist! I don’t even have an advanced degree. I am simply a dog person who has studied how genetics works so I could both breed better dogs and understand why some dogs can go so far wrong. This series of articles seeks to make everyday sense of a very complex subject so both the beginner and the hobby breeder can learn how how genes work to create a beautiful, sound and healthy dog of any color.

One of the reasons I'm attracted to Partis is because of the larger gene pool and greater outcrossing potential (and thus lower COI and hopefully fewer issues like SA, HD and PRA). We can breed to both solid-colored dogs and Partis to get the best of both worlds, and often outcrossing brings that ole parti gene to the surface - a “horrible thing” for solid-colored dog fanciers, but great for those of us who appreciate spots and patterns too.

As head of a small Standard Poodle rescue organization, I see many dogs come through my door. I've not seen many Partis in rescue, but most of those few have been poor specimens of the breed. If I didn’t know that better dogs existed, I would never have wanted to get one based on those I’ve seen!

If we are all about breeding a better dog, we must educate ourselves on how breeding works. The late Dr. John Armstrong's articles are good primers (and we’ll discuss his work in a future article), but first we need to review the basics, like Gregor Mendel's work on peas. Remember your high school biology classes? -- those boxes with the big Es and little Es and how they can combine? Let’s take a look at those peas . . .

GENETICS FOR PEOPLE WHO ARE ALLERGIC TO SCIENCE
In this section, you might get a mild rash, but you won’t come down with terminal science-itis! Relate what you read to the dogs you love: when I say “peas”, you can think “dog” - and change the traits to things like black or white, soft coat or harsh, normal eyes or abnormal eyes.

For thousands of years, primitive farmers (mostly women, as men were the hunters!) chose the best seeds to save for the next year’s crop. They had no idea why it worked, but more often than not those seeds did grow better plants. The same thing happened with animals: as people tamed sheep, cows, and horses, they discovered that limiting the best males’ access to the best females often resulted in better stock. A monk named Gregor Mendel was curious about how this worked.

Mendel liked to garden at the monastery when he wasn’t teaching high school math, physics, and Greek to teen-aged boys. He noticed that plants (peas in particular) seemed to pass certain characteristics to later generations, and that some of those traits even skipped generations, seemingly hidden for generations before they surfaced again. He studied how these traits showed up and from what plants they came, even published his research, but no one paid attention to it. In his later years, he put aside his scientific work to become the abbot of his monastery, but his research remained for biologists to find years after he died.

Mendel's research was with plants, but what he discovered applies to every living thing because the way traits are inherited are essentially the same for all.

WHAT MENDEL FOUND
Gregor Mendel bred pea plants over many generations and discovered that certain traits show up in offspring without any blending of the parents’ characteristics (also called “traits”). For instance, pea flowers are either purple or white--he never got pink or lavender. Mendel saw seven traits in peas that only showed up “this way” or “that way”:

1. Flower color is purple or white
2. Flower position on the stalk is sideways or at the end
3. Stem length is long or short
4. Seed shape is round or wrinkled
5. Seed color is yellow or green
6. Pod shape is puffy or flattened
7. Pod color is yellow or green

The idea that traits could be “either-or” was a surprise. Experts in those days thought all inherited traits blended from generation to generation, similar to some misguided dog breeders today who think that if they breed a refined dog to a chunky dog, they will get moderate dogs. It’s MUCH more complicated than that.

Similarly, others thought there were hereditary "particles" that were affected by the things that happen during a lifetime -- the "inheritance of acquired characteristics”. According to this theory, dog breeders felt that if they docked their dog’s tails for many generations, puppies would be born without tails. It just is not so! Those are not the types of characteristics that can be inherited.

Back to Mendel: he used garden peas because they are easy to grow and can pollinate either themselves or each other. He bagged the peas to isolate them and used brushes to pollinate them the way HE wanted. He kept careful notes; without records, he would not have been able to keep track of which pea was doing what with another pea, and how the “kids” turned out.

His starting peas each had two identical forms ( or alleles, pronounced “ah-LEELZ”)) of the gene for a color trait--2 yellows or 2 greens. In genetics talk, this means they were “homozygous” (ho-mo-ZY-gus; “homo-“ is Greek for “same” and -“zygous” refers to “gene”). Alleles don’t generally come singly; they come in pairs. For this reason, you can have two of one kind or one of each kind, one donated from each parent. This first generation had the same allele, one yellow-seeded, one green-seeded. If they were bred only by color, they would have only that color.

When he pollinated the greens with the yellows, he discovered all the peas in the first offspring generation (F1) were “heterozygous” (“hetero” means “different”) because these “children” peas inherited a yellow and a green allele from each of the parents. It becomes clearer when we use a Punnett square (see below) to look at the actual “genotype” (JEE-no-type; means “genetic traits”) of the pea plants instead of only the “phenotype” (FEE-no-type; physical traits we can see).

Setting up and using a Punnett square is easy once you understand how it works. You begin by drawing a grid like that for tic-tac-toe.

Next, you put the genes for one parent across the top and that for the other parent down the left. Only one letter goes in each box for the parents. It doesn’t matter which parent is on the side or the top. For example, if the parent pea genes were YY (for the yellow allele) and GG (for the green), it would look like this:

Next, fill in the boxes by copying letters across or down into the empty squares.  This shows what the first offspring generation (F₁) would look like.

Each of the F₁ plants got a Y allele from one parent and a G allele from the other.  When the F₁ plants bred, each had an equal chance of passing on either Y or G alleles to each offspring.

Think of it this way: we SEE a black dog.  Sometimes we KNOW, based on a litter from this dog, that he can produce white.  What we SEE is the phenotype (him being black); what we KNOW is the genotype (he can produce white).  Now, he might also produce, cream, blue, silver and brown, but we haven’t seen it, so we DON’T KNOW if those colors are in his genotype.  Yet.  Let’s keep it simple for now! 

When Mendel cross-pollinated peas that either produce yellow (Y) or green (G) pea seeds only, he found that the first offspring generation always had yellow seeds.  However, the next generation (F₂) consistently had a 3-yellow to 1-green ratio.

With all of the seven pea plant traits that Mendel examined, one form appeared to be “dominant” (the allele we see) over the other. It hid (masked) the other allele’s existence! So, when we SEE a yellow pea seed (when the genotype for pea seed color is YG [heterozygous]), the phenotype is the same: yellow. However, the dominant yellow allele doesn’t change the recessive (the hidden allele) green one in any way. Both alleles can be passed on to the next generation unchanged.

If you SEE yellow, but when you breed them together you get mostly yellows with a few greens, then you know the phenotype is yellow but the genotype is heterozygous (mixed) for green and yellow, i.e., YG.

If you SEE yellow, and when you breed them together you always get all yellows, then you know the phenotype and the genotype is homozygous (same) for yellow (YY).

If you SEE green, you will only get green: it has to be homozygous for green, as is the genotype (GG).

Clear as mud, huh? Keep practicing; it gets easier with time.
Translated to dogs, this doesn’t mean that, for instance, in a litter of four puppies, that three would be black and one parti every single time! It means that if the same dogs produced 20 litters of puppies in varying numbers (litters of 12, 3, 9, 7, 7, 10, 4, 11 and so on) that, over time, the ratio of all those litters would average three black puppies for every parti.

This 3:1 ratio happens in later generations too. Mendel came to three conclusions:

1. The inheritance of each trait is determined by "units" or "factors" that are passed on to descendents unchanged (these units are now called genes);
2. An individual inherits one gene from each parent for each trait;
3. A trait may not show up but can still be passed on to the next generation.

Mendel's work resulted in two principles:

1. The principle of segregation, which says that for any particular trait, only one allele passes from each parent to an offspring. Which allele is inherited is a matter of chance;

2. The principle of independent assortment, which means that different pairs of alleles are passed to offspring independently, making new combinations of genes possible.

For example, a pea inherits the gene for purple flowers instead of white ones (PW, maybe, or PP). This does not mean it will also inherit the ability to produce yellow pea seeds (YY or YG). The genes for independently assorted traits are located on different chromosomes.

Some readers are beginning to suspect there is more to this. “Hmm,” they say, “If there are independently assorted traits, I’ll bet there are dependent traits.” Smart reader! Yes, there are. This is why we have cream-colored dogs, or blues, or odd-eyed dogs in some breeds. We’ll talk more about those in a future article. These types of traits directly affect the health, mental soundness, and physical looks of our dogs. If you don’t understand them, you will forever be in the dark when you are breeding; and if a buyer doesn’t understand them, they will buy poorly bred dogs when it’s possible to learn, buy, and breed smarter.

Genetics for the Poodle Lover Glossary 

TERM	DEFINITION
allele	Form of a gene
autosomal recessive	One way a trait, disorder, or disease can be passed.  An “autosomal recessive disorder” means two copies of an abnormal gene must be present in order for the disease or trait to develop.  Sebaceous Adenitis is suspected of being an autosomal recessive.
blending	An inheritance pattern of incomplete dominance. The children inherit characteristics that are in between those of the parents.
carrier	Not something you put your puppy in! This is an individual who has a hidden (recessive) trait that will only show up if bred to another with the same hidden trait.  Carriers often do not show any signs of the trait but can pass it on to their offspring.
codominance	The situation in which two different alleles for a trait are expressed unblended in the phenotype of heterozygous individuals.  Neither allele is dominant or recessive, so that both appear in the phenotype or influence it.  Type AB blood is an example.  Such traits are said to be co-dominant.
Co-efficient of Inbreeding	A way of gauging how close two siblings (littermates, members of group with same father and mother) are genetically to one another. The coefficient of inbreeding is the probability that a person with two identical genes received both genes from one ancestor.
COI	Co-efficient of Inbreeding
dominant	Form of a gene or allele that masks the other one.
F	The symbol for the coefficient of inbreeding.  We use F1 to note the number of genes in common in the first generation from parent, F2 to symbolize the grandchildren etc. A measure of how close two individuals are genetically to each other.
genotype	The genetic makeup of an individual.
HD	Hip dysplasia
Hip dysplasia	A condition where the hip joint is not formed properly. The socket is shallow and the head of the femur is not well rounded.  Thought to be partly or wholly hereditary in many species.
independent assortment	Different pairs of alleles are passed to offspring independently, making new combinations of genes possible.
masking	An interaction in which one gene suppresses the expression of another.
non-dominant	When both alleles on a gene are partially expressed, often producing an intermediate phenotype.  For instance, a red flower and a white flower may produce a pink flower.
Outcrossing	The crossing of two unrelated parents, to produce seed/offspring as genetically variable as possible
phenotype	The outward appearance of an individual.
Polygenic	Two or more genes.  Eye color is polygenic, determined by a number of genes.
PRA	Progressive Retinal Atrophy
Progressive Retinal Atrophy	Progressive retinal atrophy (PRA) is a group of genetic diseases seen in certain breeds of dogs and, more rarely, cats.  Characterized by the degeneration of both retinas, causing progressive vision loss ending in blindness.
Punnett square	A way to figure out all the combinations of genotypes that can occur in children, given the genotypes of their parents.  It also shows us the odds of each of the offspring genotypes occurring.
SA	Sebaceous Adenitis
Sebaceous Adenitis	Inflammation of a sebaceous (oil-producing) gland. In dogs, sebaceous glands are found on the top of the tail near its base, and at the junction of mucous membranes with skin.
segregation	For any particular trait, only one allele passes from each parent to an offspring.
Thyroid disease	Abnormality of the thyroid gland and its production of thyroid hormone
von Willebrand’s disease (vWd)	A common inherited bleeding disorder (like hemophilia in humans) in which a dog is missing a substance (called a “factor”) which helps form clots.  All twelve factors are needed for clotting to happen.  Factor VIII is called 'Von Willebrand's factor.' Dogs with Von Willebrand's disease don’t have Factor VIII and bleed excessively when they are injured. Many breeds including Standard Poodles have this inherited disease.  There is now a test to prove whether or not a dog can pass it on; a “genetically clear” dog cannot carry the disease.