Beyond Mendelian Genetics
Polygenic Inheritance:
Many traits are influenced by multiple genes (polygenic), rather than a single gene. For example, traits like height, skin color, and weight in humans are controlled by multiple genes interacting together.
In dogs, traits such as coat color, size, and behavior are also polygenic, making them more complex to predict and understand.
Epistasis:
Epistasis occurs when the effect of one gene is modified by one or several other genes. This means that the expression of one gene can be influenced by the presence of other genes, adding another layer of complexity.
For example, in dogs, coat color can be influenced by multiple genes interacting with each other, which can mask or modify the expected outcome based on Mendelian genetics alone.
Incomplete Dominance and Codominance:
Incomplete dominance occurs when a heterozygous genotype results in a phenotype that is intermediate between the two homozygous phenotypes.
Codominance occurs when both alleles in a heterozygous genotype are fully expressed, resulting in a phenotype that shows both traits simultaneously.
For instance, in certain dog breeds, fur patterns and color can exhibit these types of inheritance, leading to a blend or coexistence of traits from both parents.
Genetic Linkage:
Genes located close to each other on the same chromosome tend to be inherited together, a phenomenon known as genetic linkage.
This can affect the expected ratios of inherited traits, as linked genes do not assort independently.
Environmental Influence:
Environmental factors can influence gene expression through a process called epigenetics. Factors such as diet, stress, and exposure to toxins can affect how genes are turned on or off, impacting the phenotype.
For example, the development and behavior of dogs can be significantly influenced by their environment and upbringing, in addition to their genetic makeup.
The interplay of multiple genes, environmental factors, and epigenetic modifications all contribute to the phenotypic outcomes in dogs. Understanding these complexities requires advanced genetic tools and techniques, which continue to evolve and enhance our knowledge of canine genetics.
Genome-Wide Association Studies (GWAS):
GWAS analyze the entire genome of many individuals to identify genetic variations associated with specific traits or diseases. This approach has uncovered many genetic variants that contribute to complex traits in both humans and dogs.
For example, GWAS has been used to identify genes associated with hip dysplasia and certain cancers in dogs.
Modern genetics has shown that the inheritance of traits is more complex than the simple dominant-recessive model proposed by Mendel...who himself I believe stated that his work on peas should not be so directly correlated to the much more complex human.
Dogs have 39 pairs of chromosomes, including 38 autosomes and 1 pair of sex chromosomes (X and Y). The canine genome contains about 2.4 billion base pairs and around 19,000-20,000 protein-coding genes. Over 340 dog breeds have been developed through selective breeding, each with unique physical and behavioral traits. However, selective breeding can also concentrate genetic disorders within breeds. Disorders include hip dysplasia, progressive retinal atrophy (PRA), epilepsy, cardiomyopathy, and others. For instance, the prcd form of PRA affects breeds such as American Cocker Spaniels and Labrador Retrievers.
cite
For more detailed information on dog genetics and the complexity of inheritance, you can explore resources from the AKC Canine Health Foundation, Embark Veterinary, and the Orthopedic Foundation for Animals.
