Beginning Genetics

Beginning genetics for Pit Bull People

By Scot E. Dowd Ph.D.

Introduction:

I was asked, encouraged and finally talked into producing an article that will ultimately be a series of articles. These chapters when taken together will serve as an in-depth primer on Dog genetics and the science (and art) of breeding.

I do not see an easy 1 page way to present the past 100+ yrs of research related to genetics and inheritance, therefore I will publish one section at a time and this chapter serves as the first segment.

This primer will introduce the premier concepts of genetics and inheritance and will introducing terminology that is vital to the discussion of future and much more advanced topics.

I hope you find my writing style easy to follow. I will do my best to lead you gently into the arms of the science of Dog Breeding so you can better challenge your art (or lack thereof) with knowledge.

WHAT IS THE ART OF DOG BREEDING?

One of the finest examples of red nose phenotype

TRUE ART

True art in the breeding of dogs is an inherent GIFT some would say. It is not a talent that you can truly learn. Such skills can be sharpened by long experience. As an example, Rembrandt had a "God given" gift for painting. I am not a good painter yet I could after a hundred yrs of study learn to paint a picture that looks like a Rembrandt. Yet, I would probably never come close to true artistry would I? All I would be painting is a carefully refined imitation; I might as well put a real Rembrandt into a scanner and save myself a hundred years. Similarly if you do not have a true talent for breeding that shows in how many titles the puppies you produce earn then maybe you should leave breeding to those who do have the talent. Maybe I have fun painting, maybe I become good at it, maybe I make money (this does not apply to ethical breeders today however), yet a true artist or a true art fancier would spot my fabrication from a mile away.


Rembrandt's (TheFeast of Belshazzar)

So why learn genetics if I am gifted?

Still using the painting example, the primary rule is that a great painter never divorces his art from science. Even if a breeder is blessed with this elusive “gift” (but more importantly without it) the breeder must rely heavily on knowledge and careful refined and well planned experimentation to ultimately develop the embodiment of their "Ideal APBT".

I STRESS "KNOWLEDGE" HERE. Even a moron can experiment with watching their dogs mate. You must develop and earn knowledge of the science behind dog breeding to ever be truly successful. This is where art ultimately converges with science. Let me state that merely knowing and being able to spout a few genetic terms such as “line-breeding” or “recessive” does not give one an honest or full understanding of breeding principles, let alone the untold genetic complexity contained within a single dog.

Just to give you an understanding of how complex the breeding of dogs can be, think about the following: The dog has 78 (39 pairs) Chromosomes, the human being has 46 (23 pairs), the green pea has 14 (7 pairs), and the fruit fly only 8 (4 pairs). Yep it is probably much easier to breed good human stock than good dog stock. You could say it is twice as difficult to breed a good dog as a good human.

I hope this has given you some idea of the magnitude of my challenge to you. My challenge to you is to actually learn and comprehend dog genetics and the remoteness (unreachable remoteness) of obtaining complete understand of what is happening genetically, when you breed two dogs together. (YEP, there it is!!!!!? Let me say it plainly "no matter how much you know, you really do not, nor will you ever, know enough "PERIOD"). HERE I SAY IT a different way, A TRUE breeder WITH ETHICS MUST becomes a lifelong student of genetics and inheritance. A lifetime of learning will not dissuade a dedicated breeder, but will excite them. If you do not have "THE LOVE" the true and honest desire to be the best, you will probably never find the time to learn about genetics, you will find many excuses not to continue to read this primer for instance.

YEP, I hear it in the back of your mind already "Look at the great dogs I have produced... I did this without genetics... I have the gift... IF you examine your thoughts truthfully and this is your conclusion then please go take your dogs to a spay/neuter clinic. If you think your dogs are perfect you have what is known as kennel blindness. Even the back yard breeder with scatterbred mix breeds thinks his dogs are exceptional representations of the breed. Personally I see tons of faults in my ADBA and UKC Grand Champion show dogs. I see things they are lacking, or characteristics that are overdone, and I see many qualities that keep them from being the perfect piece of dog art. I love to learn about EVERYTHING but especially about dogs and genetics and art.

Here is the challenge I give to you and the challenge you should give yourself, if you are unwilling or unable to dedicate the time to become a student of genetics (you can quite honestly start here with this primer), then I suggest you spay and neuter your dogs and leave breeding to those who love it enough to CONTINUALLY better themselves and in so doing to FIND MORE IMPROVED TECHNIQUES to better the breed.

ME

Brief words about me. I love the breed, I knew a true artist, I realized (and this famous dog man told me) that the future road to being a true artist was gaining advanced scientific knowledge, I went to college to study genetics, got a Ph.D., then and only then did I feel I could step in and probably breed successfully, OHHH let's not forget I have become one of the most avid students of breed type, working temperament, and conformation. To give you an example of the first and most important step to improving the breed.. It is something that I mentioned previously: I see more faults in my own dogs than anybody possibly could. I study my dogs and challenge myself to critique them. Hey! I am my own dogs biggest critic. Don't get me wrong, I am also my dogs biggest fan!

I have proven, maybe not that I am an artist of dog breeding (I did produce the first ever Dual GRCH ADBA/UKC Grand Champion and my foundation bitch is now the top producing UKC dam), but more importantly however (and what you should be concerned with as you read).... is someone highly qualified to teach genetics. I am also someone who loves this breed and wants to give something back to the breed, I do this by providing something free of charge to those who love them as much as I do. This primer of genetics and inheritance is a gift! I hope you appreciate it and take time to read it and let me know what you think.

Prelude to the genetic primer: What separates the APBT from the German Shepherd?

Lets start by defining BREED from a genetic standpoint: A specific breed of dog has been developed throughout the years by breeding one dog to another (duh!). Over time the dogs were eventually and selectively chosen for a particular function and ultimately they become highly specialized at the particular task for which they were being selected. The APBT was developed for a wide range of tasks from herding and guarding sheep, to protecting children on the farms, to catching rank bulls, and yes they were also developed to be really good at fighting other dogs.

After a hundred or so years (60 or so generations) these specialized animals in the United States begin to develop a particular look (type). During this process of selective breeding, what has happened genetically is that a great many phenotypically characteristic gene pairs became properly aligned or homozygous among all members of the breed. The key here and what actually defines a particular breed is that these gene pairs will remain aligned if any member of the breed is bred to any other member. In other words the gene pairs that create the overall look, temperament, and drives of the APBT have been focused in such a way that the breed has a specific, recognizable, and standard type. Even when very diverse germ lines are bred together these cornerstone gene pairs will remain aligned.

This is good news because they will breed true for hundreds and hundreds of characteristics.

(NOTE: COME BACK TO THIS AFTER THE PRIMER AND READ ITAGAIN YOU WILL REALLY APPRECIATE IT THEN!)

BYBers and Breeding

Because the breed is established and so many gene pairs (alleles) have become properly aligned it is also unfortunately true, that someone with no knowledge of genetics (or desire to read even a fun lecture such as this) and an ignorance of APBT standards and “type” can allow any two randomly chosen, backyard bred, newspaper bought, pit bulls to copulate (as long as another (german shepherd) mutt down the street does not get involved) and this will produce "something” that looks like an APBT. The "breeder" will even convince themselves and unwary buyers that these dogs are truly awesome examples of the breed (This is known as Kennel Blind).

To the “true” artist and connoisseur of breed standards, breed Conformation, and working type, the “APBTs” produced by this genetic pair may be the equivalent of a 3 yr olds finger painting (or my previous imitation of Rembrandt). Yet still the pups WILL carry a great many of the characteristic traits that broadly (I repeat broadly) define the APBT. To the publics untrained eye they will look like a "pit bull".

MUTTS HEINZ 57s- Not pit bulls or even Pit bull mixes.

Similarly if an APBT is crossed with another breed or a mutt many of these aligned traits will be carried over and many phenotypic traits of the APBT will be dominant and the resultant MUTT will resemble to a lesser or greater extent an APBT. This mutt, to the untrained eye, will also look like an APBT.

I hope from this you see the problem in relation to BSL? Suddenly we have something that is no longer an APBT, yet is a creature that still looks something like an APBT. What happens if this mutt bites someone?? The dog is a mutt genetically, is no longer an APBT, but because it has retained some APBT breed type and has phenotypic traits similar to the APBT it is called a pit bull.

Linebreeding

A world apart from the previous example we also see breeders that are more educated or maybe lucky enough to take a much safer road in the breeding game. These are the individual breeders that obtain quality dogs and line-breed a well developed and established line that has been created by a true artist. In all likelihood the art will continue to be copied to various extents. Just like in a Xerox machine. It may never be as good, in a few instances it may be better. With line bred dogs and a bloodline that has been established by a breeder-artist (hopefully using sound genetic based breeding practices and ethics) there are many more desirable gene pairs aligned than there could ever be in the scatter-bred dog for instance. Because of this increase in focused and desirable alleles, those who line-breed, within this bloodline, will continue to maintain homozygous alignment of many more traits than our scatter-breeder BYBer from the previous example (this will make more sense the further you make it in this primer). There may never be a dramatic improvement in the quality of the artwork and in all probability with continual line-breeding without constant and consistent and appropriately chosen outcrossing (or backcrossing), there will tend to be an increasing thinning of the paint “so to speak”. There is a term for this and a reason which we will discuss in time. Still, this type of line-breeding is a great thing and is very honorable and those who spent their lives developing such a bloodline may even appreciate someone maintaining it or developing off of it. Indeed these breeders will or should encourage these new generation breeders to become educated in the science of breeding. This is true mentoring!

(We will also discuss mentoring in other chapters of the encyclopedia).

A more in-depth look at the concepts of line breeding, the intricacies and importance of out-crossing, the stupidity of scatter-breeding, and the importance and dangers of inbreeding will all be discussed as this primer progresses.

Note of history

One thing I MUST stress about the art of breeding: There is a saying that” Art and beauty are always in the eye of the beholder” and only the rare artist produces work that is adored by all. In the case of dogs, art must be expressed within the boundaries of working type (canvas if you will). We must seek the favor of the breed art critics (Conformation judges) even if we feel that WE KNOW BREED TYPE. We may think a big huge bowling ball of a head is what an APBT should have, but in actuality this goes directly against breed type. IT is against the functional characteristics that defined the breed during history. If you do not know why a huge head is wrong from a Conformation perspective on a “truly standard APBT” please read more on the Conformation site especially on the head page. If you also think that an overabundance of bone and substance is what is “typical” or "looks good" for the APBT, then I defy you to show me any dogs from back in the original working dogs (fighting dogs for instance) that had bodies short-wide and thick, like an English Bull Dog.

No the pit bull dogs were all around gladiators, not sumo wrestlers. We as breeders cannot (and still be considered artists of the breed) redefine the original performance perfected standard. We cannot take a dog that should be able to compete AND Excel in agility, Obedience, herding, weight pulling (all at the same time) and turn them into a overdone tank that cannot get all four feet off the ground at the same time. Why would we turn a dog that has been optimized for performance into something that cannot jump a 3 foot hurdle in agility?

see the GR CH from history page in the pit bull galleries pictures site if you need a refresher on proven breed type).

Fad verses Fact. Do you want to be a true artist or considered to be a Fad Breeder?

The message I am trying to convey and I will fall back on my analogy is that, we as breeders cannot be impressionistic in our art, we must be classical artists, perfect the breed, not Surreal Impressionists that breed for outrageous characteristics.
.

Classical Breed Standard Interpretations (Michelangelo's Adam from the Sistine Chapel)


not impressionistic or Surreal Interpretations (Salvador Dali's The degeneration of the Persistence of Memory)

In the art of dog breeding!(Note: One of my favorite painters is Salvador Dali, but let us not seek impressionistic interpretations of the APBT standard)

THE FIRST STEP OF THE PRIMER ON genetics

Genetic Beginnings (are you willing to learn?)

This is where it all begins.? Ask yourself “Do I really want to learn this genetics and inheritance stuff”? If the answer is NO or "I don't have time for this" or "I'll do it later" etc. etc., I'll say it again, then you should load up all your dogs and pay a visit to a spay/neuter clinic. However, if you are fascinated, not too pissed off from my challenges above, and you do decide to continue on, then you are on the right track. I will try and stick to genetics rather than fluff from here on out!

HERE WE GO:

Let us start this by providing an overview of Mendelian genetics. The goal is to introduce you to the most basic laws of inheritance.

The first concept is that DNA encodes the essential "information" that determines all breed characteristics. The working structures that make up an APBT can be thought of as form or substance, which is at the most fundamental level defined genetically. Note: the term substance in genetic terms does not refer to heaviness of muscle or bone as used when discussing breed type. In other words, "DNA encodes all the information that is needed to give type."

Painting a mental picture of how DNA fits into the big picture

Think of all the characteristics of your dog as individual paired packets of information. The black nose, the red nose, the temperament, strong working drive, dog aggression, good angulation, straight front, laziness, weak underjaw, tendency to be fat, tremendous muscle tone, big head, too long of a tail, straight topline, short back, powerful reach and drive and essentially all other characteristics that make up, or are missing from, a specific “breed type” or “line type”. All these traits are determined by paired packets of information encoded in DNA. In a simplistic form the sire of a dog provides one packet and the dam provides the second packet to create the dual packets of information for the puppy. The two packets determine how the puppy’s characteristics will develop.

So if you pair together a dam with good angulations with a sire with good angulations you will get puppies with good angulations right? Well THIS IS NOT PRECISELY TRUE, WE WILL LEARN WHY SOON. HOWEVER, LETS KEEP IT SIMPLISTIC AT FIRST BEFORE DELVING INTO THE SUBTLETIES OF INHERITANCE.

DNA within the grand scheme

To help with the understanding I like the following symbolisms to put together a mental image.

Take “your” perfect image of “your” perfect APBT (hopefully something that fits the breed standard perfectly). Think of this perfect dog as the perfect BOOK (DOG = BOOK). This BOOK is a masterpiece, leather bound and hand stitched lettering, the best edition of the best book you have ever seen and read (Top 10 #1 dog of all time) and has all of your favorite fonts and pagination (type). The book is written in a particular language that is universal (genome), the book is divided into chapters (chromosomes), these chapters are made up of paragraphs (loci). The paragraphs are made up of sentences (genes), these sentences are formed by words (codons), and these words are created by single letters (Deoxyribonucleic acid or DNA molecules). Thus, we see that DNA is the most fundamental unit of heredity.

goes to goes to

DNA:

DNA is an amazing molecule (even to a geneticist) and its primary and most magical characteristic is that it has, over billions of years of evolution, developed the ability to replicate. In other words it is able to make exact copies of itself. This ability to make functional copies is the basis for heredity. It is not the parent’s genes which are passed on to the puppies but copies of the parental genes. Another thing I’d like to throw in here is that: It is not copies of all the parental genes (remember the dog has two of every gene) it is only half of the parental genes that are passed to any given puppy, as we shall eventually see.

The example noted above of pairing two dogs with correct type (angulation for instance) to produce dogs with good type does hold true to a certain extent. It is logical but we will find out more about the why and how, as we proceed. This example does lead us nicely to our primary inheritance topic.

The issue that we will drive home in this first segment of our primer. If you pair together a dam with too little angulations with a sire with too much angulations will they combine together to create dogs with perfect angulations? The answer is NO! Yet, I have heard this from so many breeders. I just smile and node in agreement because...well you know why! Ok why is this faulty logic? The reasoning behind it is simple and will become very clear as we move along in this tutorial and the rest of the chapters that will follow. The prevailing notion I find when I listen to, or read, what breeders say about genetics is that they feel the spermatozoon and egg contain a sampling of “essences” from the various parts of the parental body. Magically; at conception, these essences are somehow blended perfectly together to resulting in the development of the new offspring. This idea of blending inheritance is thought to account for the fact that offspring typically show characteristics that are similar to or a perfect mixture of both parents. The truth of this is that off-spring are rarely an intermediate blend of their parents' characteristics.(This Blending inheritance was the most popular model of inheritance hundreds of years ago but now is a discredited model.

We now know that the characteristics of an individual do not result from the smooth blending of fluid-like influences from its parents. As we stated before inheritance is particulate in nature, not fluid.

INHERITANCE 101:

The first stage of inheritance is the production of either the sperm or the egg.

Do not view the sperm and the egg as perfect little genetic representations of each parent. Do not consider that when these two "sex" cells combine (one from rover and one from foxy) and that there is a blending to create "roxy". We noted previously that combining a dog that lacks angulation with a dog with too much angulations will NOT likely produce a dog with perfect angulation. Again this concept cannot be stressed too much, or too often, at the beginning of our learning: There is no melting together or blending of genetic traits. Most likely from such a cross you would get half the litter that has poor angulation and half the litter that has too much angulations (a couple pups may have great angulation but this is probably because the grandparent had good angulation). This prediction and example are also too simplistic but it serves to distinguish between blending and particulate inheritance.

Particulate inheritance means that genetic information is transmitted from one generation to the next in discrete unchanging (not accounting for evolutionary and mutation events ;-) units ("genes").

Here is a question for you breeders. “Would you rather have a dog with an good body structure and a poor head piece OR a dog with the best headpiece ever, but poor body structure?” – My answer is that I would take the former. Stick around for subsequent segments of this primer and we will find out why!

Let us attempt to analyze the patterns in which phenotypes (breed types “sort of”) are inherited in the APBT. We shall see that many of these patterns are ultimately regular and predictable on an individual level. HOWEVER, there are other factors that come into play that make logical breeding much more difficult than combining two dogs with good traits. Yet it is this regular pattern of inheritance, as we shall see, that first led to the concept of the gene and the theory of inheritance. It is here we have begun our journey.

PATTERNS OF INHERITANCE:

(purple flowers and red noses: or black is better to sniff white with) read this joke again and when you understand it you are beginning to understand genetics.

In 1865 Gregor Mendel (a monk) refuted the theory of blended inheritance (GRIN It was popular back then, not just among dog breeders, but the entire scientific community) and instead he proposed a theory of particulate inheritance. According to Mendel's theory, characters are determined by discrete paired units of information that are inherited intact down through the generations (read that sentence 10 times until you memorize it! Trust me this will help cement the concepts). Mendel’s experiments were simple and elegant and now they serve as a framework or introduction to a more detailed understanding of the mechanisms of heredity.

READER: OK that’s it!? IF you talk about peas I am leaving!
ANSWER: Well if you cannot grasp the concept of inheritance through the following simple and logical Mendelian experiments then you should go visit the spay/neuter clinic immediately.

Gregor Mendel was at a monastery at Brünn, where he began experimenting with plant hybridization (breeding). HE became famous through a series of classical studies that posthumously (after he died) earned him the distinction as the founder of the science of genetics. Mendel's studies constitute an outstanding example of good scientific principles. Good scientific principles are something from which your art-science of breeding will benefit tremendously. Mendel chose research material with defined phenotypes (color, texture etc.), he carefully constructed experiments, he documented his results carefully, and he used statistical analysis to validate his hypothesis.

Yep, Mendel studied the garden pea. The pea has only a few chromosomes, and compared to the dog's massive number of chromosome, it is a very simple model for breeding. Maybe before breeding dogs, you should learn to breed a better pea. If you can do this then you might attempt to tinker with something as complex as the dog genome. Mendel chose seven different characters to study (we will discuss at least one of these). The word character in this regard means a specific property of an organism (phenotype); geneticists use the term phenotype as a synonym for "characteristic" or trait.

OK for those of you who have stuck around this far (congradulations) I will also temper this dry discussion of peas, by throwing in a parallel virtual APBT experiment using black nose and red nose APBTs.

DOMINANT AND RECESSIVE

MENDEL: For each of the characters that he chose, Mendel obtained and bred stable lines of the garden pea. To ensure these lines were stable he selectively bred them for two years to make sure that they were pure (IN other words he linebred and inbred different groups of peas for specific characteristics). A pure line is a population that breeds true for (shows no variation in) the particular character or phenotypes being considered; Mendel had made a clever beginning: he had established a fixed line of plants for his future studies so that any changes observed, subsequent to deliberate manipulation in his research, would be scientifically meaningful.

APBT BREEDER: In our experiment we have created two bloodlines of APBT. One of these bloodlines always produces black nose dogs, the second separate bloodline always produces red nose dogs. We have bred these bloodlines for 4 generations to ensure that this particular trait always breeds true. The red nose never produces a black nose and the black nose never produces a red nose.

MENDEL: Two of the pea lines studied by Mendel bred true for the phenotype of flower color. One line of peas bred true for purple flowers; the other, for white flowers. Any plant in the purple-flowered line when crossed with other plants from the same line produced seeds that all grew into plants with purple flowers! The white-flowered line, similarly produced only white flowers through all generations. Each pair of Mendel's plant lines can be said to show a stable trait or phenotype (flower color). Thus, Mendel has good contrasting phenotypes to start his experiments on heredity.

DEFINITION: The term phenotype (derived from Greek) literally means"the form that is shown"; it is the term used by geneticists today. Phenotype is the form that is shown, but the term Genotype is more important from a breeding standpoint. The genotype is the form that is shown combined with the form that is hidden.

In his next step after developing two "true lines" of pea flowers, Mendel pollinated a purple-flowered plant with pollen from a white-flowered plant. We call the plants from the pure lines the parental generation (P). Strangely enough, all the plants resulting from this cross had purple flowers. This first generation is called the first filial generation (F1). (The subsequent generations produced by backcrossing the F1 are symbolized F2 , F3 , and so forth.)

APBT BREEDER: The breeder crossed a black nose sire with the red nose dam. The sire and dam from the original pure lines are the parental generation (P). In this case all of the puppies (F1 generation) from this breeding had black noses. What happened to the red noses? Shouldn't we see something like reddish black? NO!

MENDEL: If one pure-breeding parent is purple flowered and the other is white flowered, all plants in the F1 have purple flowers. The purple flower color in the F1 generation is identical with that in the purple-flowered parental plants. In this case, the inheritance was not a simple blending of purple and white colors to produce some intermediate color. To maintain a theory of blending inheritance, we would have to assume that the purple color is somehow "stronger" than the white color and completely overwhelms any trace of the white phenotype in the blend.

Why was the red nose phenotype (or the white flowers) not expressed in the F1 pups? Mendel actually coined the terms dominant and recessive to describe this strange phenomenon. The purple flower/black nose is dominant to the white flower/red nose and the white flower/red nose phenotype is recessive to the purple flower/black nose phenotypes. Thus we can see that if we breed a true line of black nose dogs to a true line or red nose dogs the F1 (first filial generation) will be black nose because the black nose gene is dominant.

As we already mentioned and continue to stress, it becomes very difficult to apply the theory of blending inheritance to devise an explanation of these results.

GENES OCCUR IN PAIRS

Mendel then selfed the F1 plants (purple flowers), allowing the pollen of each flower to fall on its own stigma. Because pea plants have both sex organs (flower and stigma) they can be bred directly to themselves. This is termed selfing.? (different from inbreeding) Here is where it got interesting for Mendel~! While most of the flowers were purple some of the resulting plants actually had white flowers. Like magic, the white phenotype had reappeared.

Mendel did something that was amazing for the times and something which earned him the title of Father of Genetics: he counted the numbers of purple flowers and white flowers. Mendel counted 705 purple-flowered plants and 224 white-flowered plants. He noted that the ratio of 705:224 is almost exactly a 3:1 ratio (in fact, it is 3.1:1).

APBT BREEDER: With dogs the closest we could come to selfing, would be inbreeding an F1 male to an F1 female (brother and sister). After doing this virtual inbreeding we find that out of 8 puppies two were red noses. The other 6 had black noses like their F1 parents. Like magic these two black nose F1 dogs produced two red nose (F2) puppies. Importantly, just like in Mendel’s experiment this is also a 1:3 ratio of red nose to black nose.

WAIT: It is easy to understand if black is dominant and we breed a black nose P sire to a red nose P dam that all the F1 generation puppies would have black noses, but how in the world did we get red nose puppies when we breed two black nose F1 dogs?

YEP THERE IT IS: The overwhelming lesson from this is that, even though the F1 dogs were black nosed, the dogs themselves carried the hidden ability to produce rednose F2 pups (genotype).
The answer is simple and gives us our second concept: GENES (actually chromosomes) IN DOGS OCCUR IN PAIRS, EXCEPT IN THE EGG AND SPERM (remember we keep repeating this to ourselves from above).

Lets say it again, Genes occur in pairs in the dog. The dog has 39 chromosome pairs (total of 78 chromosomes). This is what is meant by diploid (diploid = double). There is another term of importance which is haploid (haploid = half) that describes the genome of the egg and sperm. Those definitions are not precise but will make the terms easier to remember. The figure below, in addition to showing haploid and diploid, will help us illustrate several more terms and concepts we need to understand.




GO OVER OUR RED nose BLACK nose EXPERIMENT USING THE DIAGRAM
In the figure above the top blue blob represents our original pure blacknose homozygous B/B (Parental strain of black noses) the yellow blob represents our original pure (parental) strain of red noses homozygous b/b . Notice that there are two letters in the blobs. Yep, these represent the gene pairs (diploid-double). B= Black nose gene and b = red nose gene. Each of these original bloodlines has been line bred and the characteristics of the specific nose colors have been aligned.

TERM: The word we use to describe when we have two exact or functionally exact copies of the same gene on both the maternal and paternal supplied pairs is homozygous. Thus both of the P generations are homozygous for their respective nose colors.

Out of each of the P parents we see a separate smaller yet similarly colored blob, representing the egg and sperm. Notice that the egg and sperm do not have paired letters. This is because they do not contain both pairs of chromosomes. They actually are haploid (half). To repeat this, the dogs themselves are diploid but the sex cells are haploid. In essence, all the paired genes from the parents are separated somewhat randomly and the spermatazoon and egg are formed from only half of the chromosomes of the original parent. (this is segregation and we will come back to this in the next segment of the primer). In the case of nose color, the only possible genes for nose color from the red nose homozygote P generation is b and the only possible gene from the black nose homozygous P generation is B . (note this has nothing to do with whether the rednose is a male and the blacknose is a female. The red nose homozygous P generation can only produce egg or sperm that is b. The black nose homozygous P generation can only produce egg or sperm that is B.

Segregation revisited (important concepts I will repeat)
The dogs themselves are diploid but both the egg and sperm are haploid, meaning that they (unlike the actual dogs) only contain one of the two alleles encoded by the dog. This is what is known as segregation. Segregation is the next concept of importance. Segregation as a concept is vital to understanding what goes on when you are doing outcrosses, family and line-breeding. We will delve more into segregation and random selection later. However, what we mean by segregation is that when the bitch produces eggs, her chromosome pairs are segregated equally into haploid states in the eggs. Meaning: The members of the gene pairs segregate (separate) equally into the gametes. The same is true for the male. His diploid genome is segregated equally into individual sperm which are haploid. A good example to use and one we will return to eventually is sex determinant. Thus the Gametic content states that each gamete (sperm or egg) carries only one member of each pair.


Thus, when the sperm and egg combine to create the new dog these two gene pairs (one from the male sperm and one from the female egg) are combined to form a new genotype B/b, which is completely different from either parent. The F1 generation is not homozygous (B/B or b/b) for nose color instead they are heterozygous(B/b). However, as we saw the phenotype (what we see) produced in the F1 generation is exactly the same as the black nose parent because the blacknose gene is dominant The genotype is different from either parent . This is seen by the large green blob representing the F1 generation. This F1 generation can produce sperm and egg which are of course haploid but when the separation of the chromosomes occurs when the eggs or sperm is produced equal portions of B and b haplotypes are formed.

PUNNET SQUARE

Next we notice that the F1 generation (green blob) has arrows that point to the top and side of a four squared box. This box is a Punnet-square and is used to visualize the possible recombination of genetic pairs in a diploid organism. Here the two possible sperm haplotypes are on the vertical axis and the two possible egg haplotypes are on the horizontal top axis. To create the data in the punnet square we simply drop the letters from the top of the box down into each cell in the column below it. Similarly the letters on the side are placed across in each box in their own row. Below is an example of how this is done.

If we continued to experiment with our dog inbreeding and produced a few more litters of F1 dogs. Then if at random we began breeding all the black nose dogs with only other black nose dogs, in the resulting F2 litters, we would begin to see as second trend. We would find a population of F1 black noses that would not produce red nose dogs no matter how often they are bred. We would also see a population about twice this size which (like the F1 generation) produced a few red nose dogs (about 1:3 ratio just like the F1). But if we inbreed the red noses from the F2 generation, only with the red nose dogs, we would only obtain red nose dogs no matter how many times we bred them. If you understood the dominant recessive concept you begin to understand what is occurring within this F2 generation.

The answer is that in the F1 generation we have a Phenotype (seen) ratio of 1:3 but we also have an actual genetic distribution (genotype) of 1:2:1 (1 B/B: 2 B/b: 1 b/b). Which is to say that 1 out of 4 of the F2 generation are homozygous (has two identical copies of the black nose gene BOTH FROM THE P SIRE) for the black nose. Two out of 4 dogs from the F2 are heterozygous for the black and red nose genes (ONE FROM P DAM ONE FROM P SIRE). This means that they carry the dominant black nose gene which is expressed phenotypically (they have blacknoses) and they also carry a copy of the recessive red nose gene, which is not expressed phenotypically because it is recessive. Finally we also have produced 1 out of 4 red nose puppies that is homozygous for the recessive genotype (BOTH GENES DERIVED FROM THE P DAM).

Continuing to drive home the point

For this reason when we breed the homozygous GENOTYPE dominant we obtain only black nose dogs. When we breed the heterozygous dogs we get the same phenotypic mixture (1:3) seen in the original F2 generation (1 out of 4 will be red nose). This is because this heterozygous F2 population has the same genotype (B/b) as the F1 generation. If we breed the homozygous recessives we get only red nose dogs.

The final concept we have to grasp is that of Random fertilization. The union of one gamete from each parent to form the first cell (zygote) of a new puppy occurs randomly. This means there is nothing guiding the good red nose genes to align with other rednose genes. Segregation and joining of alleles occurs without regard to which member of a gene pair is carried. (this is a difficult concept and we will develop it in future chapters)

REVIEW AND QUIZ

In our previous work we discovered that phenotypic traits are the product of genes. These genes are individual packets of information. Together all these paired-packets of information combine to create type. We also came to recognize that heredity is not a fluid blending of characteristics it is particulate in nature.

Mendel’s original experiments with peas and our experiments with inbreeding have taught us very important concepts. There are two copies of each genes within an individual dog (pea) otherwise how did we get red noses from black noses? When breeding what we will get is one copy of a gene from the dam and one copy of a gene from the sire (randomly), both of which are transferred to the puppy.

Alternative phenotypes of a particular trait (red nose or black nose) are determined by different forms of a single type of gene called an allele. In example, the heterozygous dogs contain alleles for both nose colors (a red allele and a black allele). One of these alleles may be dominant which means that if both are present only the dominant is seen phenotypically.

OK I INDICATED THAT MY RED nose ANALOGY IS NOT A PERFECT EXAMPLE, HERE IS WHY!
Since we are using the black nose red nose as our virtual science experiment or example, let us take a minute to explain the functional genomics behind the red nose and black nose phenotype. Actually this is not precisely what we are talking about and as I have stated I am using a lot of artistic license using the red nose/black nose analogy in this discussion but I think it is a good tactic to make it more appealing to the APBT breeder. As we have seen in the case of our discussion of APBTs, the dominant (black) is called B, and the recessive (red) is called b. A black dog may be either BB or Bb; the red dog is always bb. Two black dogs may have red puppies if both of these parents are Bb; the b can come from each parent to produce bb in the pups. If either parent is BB, though, the combination can't produce red pups.
If both parents are red, bb, then all their puppies will be red; there is no B available from either parent to make a black pup.

The end product of most genes is some sort of biochemical substance. In the black color, the chemical is a pigment called eumelanin. This is one of a group of pigments, the melanins, which cause color in animal skin, hair, and feathers. It is responsible for very dark brown or black color.

APBTs typically have in their hair a red version of melanin, called phaeomelanin. In the black dogs, the black eumelanin covers the appearance of the red. If you've ever looked closely at a black APBT in bright light especially after he has spent a lot of time in the sun, you will see a faint red glow to his hair. The eumelanin has been bleached by the sun, and the red color is showing through.

Only the dominant version of the color gene results in eumelanin production; if the dog has two copies of the recessive version, he will have no eumelanin. His hair will contain only the red pigment, and anywhere that he would otherwise have been black, he will instead be red.


QUIZ




Here is an actual case study at least up to the F1 generation ;-) (no inbreedings have taken place)


Try and answer the following questions before scrolling down to see the answers


In the breeding represented by the pedigree below, a top 10 black nose (B/B) was bred to a top 10 red nose (b/b). The resultant puppies (F1) are black nose phenotypes with heterozygous (B/b) genotypes.

Using a punnet square answer the following 3 questions:

(A) What would happen (in theory) if we inbred these two F1 (B/b) puppies? (you should know this from above) If we had 4 puppies from this inbreeding what would (without taking into account segregation and the randomness of fertilization at this point: These are future segments) the nose colors (phenotype) and the genetic Alleles (genotype) be in this F1 inbreeding??

Lets think ahead also:


(B) What genotype and phenotypes would we get if we crossed the F1 back to the? P dam (b/b)?

(C) What genotypes and phenotypes would we get if we crossed the F1 female back to the P sire B/B)?

(answers below)



END OF SEGMENT 1 if the APBT breeders GENETIC PRIMER


What we have learned is that there are hereditary determinants that are particulate in nature (they are not fluid). We now call these particulate determinants genes

Concepts: Inheritance is not a blending of traits. Genes are discrete packets of information that are passed intact down through generations.

Some genes are dominant over others!

Genes occur in pairs in the dog (diploid).? However, in the sperm and egg there is only one copy of this gene pair (haploid).

answers to questions: