Down The Rabbit Hole: Understanding Genetics

The ever-expanding field of science, while providing answers to many questions, also generates endless confusion. Genetics is a vast realm of discovery, information, and further questions. In the canine genome, there are 76 chromosomes arranged in 38 pairs, containing genetic information. However, the actual genetic information in these chromosomes amounts to over 3 billion pairs. Among these pairs are coding genes, which contribute to inheritable traits, whether they are expressed or not. Not all coded pairs are activated within the DNA strand; some are only activated when linked with specific other pairs. Gene sequencing involves testing and documenting these genes to identify which genes are associated with specific alleles, leading to recurring traits or their mutations. Alleles are variations of a gene that differ from each other and are responsible for phenotypes, defined by the Merriam-Webster dictionary as "observable characteristics or traits of an organism produced by the interaction of the genotype and the environment."

When we are introduced to genetics in high school, the Mendelian Punnett Square is guaranteed to be drawn. This method of displaying dominant and recessive gene inheritance is classic in its historical importance for understanding trait inheritance. The Punnett Square serves as a visual tool that allows students to predict the probability of certain traits being passed from parents to offspring based on their genotypes. By filling in the squares with the alleles contributed by each parent, students can easily see the potential genetic combinations that could result from a particular cross, such as a monohybrid or dihybrid cross.

However, while the Punnett Square provides a foundational understanding of simple inheritance patterns, it does not account for the complexities that we have learned exist within the field of genetics. For instance, the real world of genetics is not always as straightforward as the dominant and recessive traits depicted in these squares. Many traits are influenced by multiple genes, a concept known as polygenic inheritance, where multiple alleles contribute to a single phenotype. This can lead to a continuous range of traits, such as height or skin color, rather than distinct categories.

Additionally, the interactions between genes can result in phenomena such as incomplete dominance and codominance, where neither allele is completely dominant or recessive. In incomplete dominance, the phenotype of heterozygous individuals is a blend of the two parental traits, while in codominance, both traits are fully expressed in the phenotype. These complexities highlight that the simple Mendelian model cannot encompass the full spectrum of genetic inheritance.

Moreover, epigenetics introduces another layer of complexity, demonstrating that gene expression can be influenced by environmental factors and experiences, leading to changes that can even be passed down through generations without altering the underlying DNA sequence. This challenges the traditional view of inheritance and suggests that our understanding of genetics must be expanded to include these dynamic interactions.

Furthermore, the role of sex-linked traits, which are associated with genes found on sex chromosomes, adds another dimension to inheritance patterns. Traits such as color blindness and hemophilia are examples of conditions that follow different inheritance rules, particularly affecting males and females in distinct ways due to the presence of X and Y chromosomes.

As such, while the Mendelian Punnett Square is an invaluable educational tool that lays the groundwork for understanding genetic principles, it is essential to recognize its limitations. The complexities of genetics encompass a vast array of interactions and influences that go beyond simple dominant and recessive traits. As our knowledge of genetics continues to evolve, so too must our approaches to teaching and understanding these intricate processes that govern heredity and variation in living organisms.

Typically, genes result in the display of more than one trait within an animal. Often if a particular gene is expressed, or turned "on" to make proteins, there can be a cascading effect on the expression of other genes and the resulting traits. In addition, while some mistakes in the code may inactive a gene and others may increase or add activity to a gene, the majority of these changes have little or even no consequences to the . The role of a specific protein is not always clear-cut and can lead to years of study to determine the full extent of its effect.

Geneticists have developed methods of using DNA Single Nucleotide Polymorphism (SNPs) to compartmentalize their area of study within the genome. These SNPs enable the examination of 100 thousand markers on the genome to be studied at one time, limiting the examination to a single area of sequence on the DNA strand that has been replaced by another. However, the data presented is only as useful as the series of rule-outs that can be applied to determine what these data spots mean; rule-outs, or associations, are determined by calculating the difference in frequency of each marker in the dogs with a disease or trait being studied, versus dogs that do not have the disease or trait. The most recent dog SNP chip has over 170,000 SNPs, and these SNPs must be be screened and compared to determine to what trait they are possibly tied to; not quick work.

In the canine world, many disorders or illnesses are labeled as "genetic" because they stem from genes within the animal's DNA. However, calling these disorders "inherited" can be misleading. While it's true that for these disorders to manifest, the genes must be present in the DNA and thus in the parents, considering that a DNA strand contains over 3 billion gene pairs, which transform into alleles and thus phenotypic traits (including these disorders), attributing an issue solely to genetics is simplistic. We understand that gene expression can depend on the presence of other genes in the genome, but the conditions that cause one gene to influence another are not yet fully understood (such as the proximity of genes in the code or the necessity of an additional protein for interaction), and multiple genes may be needed to create the specific environment for this expression. Therefore, labeling a disorder as merely "genetic" is inaccurate. Environmental factors can also activate certain genes, triggering a chain reaction that affects other genes. The vast potential on genetics of a constantly changing environment is beyond comprehension.

We hear of such concerns as Addison's disease, Sebaceous Adenitis, and Cushing's Syndrome and are taught that these issues are a result of the parents' of the dogs; as discussed above, this in a basic principle is correct, however, as the method of inheritance of the genes responsible for these disorders is complex and not fully understood, to proclaim the parents' as badly bred would be unlawful. Even a major concern such as hip dysplasia is not yet understood, although we are taught to rely heavily on radiographs to rule out phenotypic expression of this structural deformity. So far it has been discovered that two genes when apparent on the genome may be related to the expression of this issue; but they have not yet narrowed down the primary genes responsible, nor how these genes may be activated. As such, we know as little about hip dysplasia know as we essentially did fifty years ago. A breeder's lines may not exhibit hip dysplasia ever, but a particular combination (of dogs identified as 'clear' of the issue) may still result in this phenotype; we just do not know what is responsible for it genetically. For an issue such as Sebaceous Adenitis, it is thought to be an autosomal recessive issue (as explored in Poodles), however, its sporadic expression from lines without issue in other breeds (including Akita and Pyrenees) decries a straight forward inheritance. With these complications it is so far impossible to genetically test for these disorders, and breeders cannot prevent or plan around them.

Breeders once believed inheritance was similar to the Punnett Square, but as science has progressed, we've gained a better understanding. We now know that if an issue arises, the parents should not be bred together again, and the affected dog should not be bred; this is logical. The challenge lies in deciding whether to breed other offspring from the same pair that do not show any issues. Discussions with veterinarians about certain issues, like Addison's, focus on the undeniable fact that there is no way to test for it, and we cannot assume that every puppy in the litter inherited the problematic gene combination. Nor should we disqualify a dog that might carry some of the genes when it's more likely to be bred with another dog that does not carry the necessary genes, thanks to genetic variability. As a veterinarian advised my aunt in the 1970s, "Don't throw the baby out with the bathwater" when it comes to breeding. For issues like Dwarfism or NDG, which are clearly defined as autosomal recessive on known genes and can be tested for, the process is simpler: affected dogs should not be bred, and carriers should not be bred with those of unknown status. Dog breeding is not as straightforward as "101 Dalmatians" led us to believe as children.

Does this mean we should give up on genetic testing? No. What it does mean is that breeders (and owners) should be forthcoming when issues arise. It is crucial for them to reach out and communicate with genetic authorities and research institutions, such as the University of California, Davis, or the University of Minnesota genetics departments.  This data is essential for researchers to understand the underlying genetic mechanisms that contribute to these disorders. The DNA from those affected, and the patient's history, is what we need to learn from in order to begin narrowing the view on what causes these issues.

When a genetic issue is identified, whether it manifests as a physical anomaly or a behavioral concern, it is imperative that breeders document these occurrences meticulously. This documentation should include DNA samples from the affected individuals, as well as comprehensive patient histories that detail the symptoms, age of onset, and any other relevant medical information. By sharing these examples with genetic researchers, breeders and owners contribute to a collective database that can help scientists identify patterns and potential genetic markers associated with various conditions. Without such examples and the accompanying data, the scientific community lacks the necessary information to draw meaningful conclusions or to develop effective strategies for prevention and treatment.

Furthermore, collaboration between breeders, pet owners, and geneticists fosters an environment of shared knowledge and innovation. It encourages the development of more refined genetic tests and screening protocols that can ultimately lead to healthier breeding practices. This collaborative effort can also enhance the overall welfare of the animals involved, ensuring that future generations are less likely to suffer from inherited disorders.

In conclusion, the intricate world of genetics extends far beyond the simplistic frameworks often introduced in educational settings, such as the Mendelian Punnett Square. As we delve deeper into the complexities of gene interactions, polygenic inheritance, and epigenetic influences, it becomes clear that our understanding of heredity and trait expression is continually evolving. The challenges faced by breeders in identifying and managing genetic disorders in canines underscore the importance of recognizing the multifaceted nature of genetics. While genetic predispositions can play a significant role in the health and traits of dogs, environmental factors and the interplay of multiple genes further complicate this picture. As the field of genetics advances, so too must our approaches to breeding and understanding the myriad factors that contribute to the health and diversity of canine populations. Embracing this complexity will not only enhance our knowledge but also promote responsible breeding practices that prioritize the well-being of future generations of dogs.