The easy answer to the question, “How Many Chromosomes Do Dogs Have?’ is 78, or 39 pairs. However, understanding just how the number of chromosomes your dog has affects them requires a bit of explanation.
What Are Chromosomes
Chromosomes are the basic building blocks of any animal, plant, and most other organisms. They are paired, with one coming from the mother and one from the father. They carry DNA, or deoxyribonucleic acid, which is the material that makes the genes that make each and every living creature unique.
Every trait, nerve, organ, and appendage are programmed into those deoxyribonucleic acid DNA strands and the genes they contain. If you have blue eyes it is determined by your chromosomes. If you own a Siberian Husky – a dog breed with blue eyes– his eye color, as well as everything that makes them a husky and not a Yorkshire terrier, are also the result of the information contained in their chromosomes.
Every species of animal or plant has a specific number of chromosomal pairs. Human beings, for instance, have 23 pairs of chromosomes, horses 32 pairs, and maple trees 26 pairs. While the exact number of chromosomes varies from species to species, the number of chromosomes found within a species always remains the same. Amazingly, the tiniest of chihuahuas have the same number of chromosomes and the largest of mastiffs.
A Quick Genetics Review
So, how dogs, and everything else, get their 78 chromosomes. The easy answer is from their sire and dam, but again, some explanation is necessary.
Before sire meets dam, a process is known as meiosis happens. This is a two-step process during which the 39 pairs of chromosomes separate through cell division. Half of the soon-to-be parent’s genetic material is now contained in two different cells. Cell division happens again. Now you have four reproductive cells, sperm cells in the males and eggs in the females, each containing one-half of the original chromosomes. The cells that contain these sex chromosomes are known as gametes.
All the types of DNA and genes contained in the gametes of both genders are exactly the same as the ones they will encounter when they merge with another gamete, except for the sex chromosomes that determine the sex of the offspring. In the sex chromosomes, referred to as the X chromosome (female) and Y chromosome(male), the female gamete contains an extra piece with additional DNA not found in the male chromosome. If 2 X chromosomes meet then the result is a female offspring. If an X chromosome meets a Y chromosome then the result is male.
This means that a female can only donate X chromosomes to the reproductive process or more simply, all eggs are female until fertilized. Males can donate either X or Y chromosomes, in effect male or female sperm. Therefore, it is the sperm that determines the gender of the offspring.
Through the mating process, the male dog’s sperm is deposited into the body of the female dog where the egg and sperm can meet. Once this happens, the individual chromosomes and all of the DNA they contain, merge together to form a new pair containing part of the genetic makeup of each parent.
This new cell, called a zygote, begins to divide and grow. Everything that it will become, from tiny teacup poodle to massive Newfoundland, is already programmed into those 39 pairs of chromosomes.
It’s All in The Genes
Genes are made of DNA and are the specific coding used to determine the function of each cell in your dog’s, or any other creature’s body. Similar to code written for computers, genes are programmed to send specific information to the cells to get them to behave in a specific way. Each gene contains material from both of the paired chromosomes and so is affected by the genetic makeup of both parents.
Genes are responsible for every trait an animal, plant, or human has. Like computer programming, sometimes there is a glitch and the information does not get passed on correctly. This is known as a genetic mutation.
Cell Division and Genetic Mutation
Occasionally, something goes wrong when the chromosomal pairs separate and then reform with new DNA. Pieces can get broken off or not separate properly leading to missing or extra genes. This leads to a situation in which either incomplete or incorrect information is passed onto the cells that are dividing rapidly to form a new dog. Many chromosomes contain mutated genes.
Sometimes these mutations have drastic effects resulting in the death of the fetus or a puppy that is born horrible disfigured. Sometimes the effects cannot be seen at first but can lead to diseases such as diabetes, cancer, and heart problems. Other times the mutation is as harmless as a hair of a different color or a dog that is larger or smaller than expected.
It is these harmless mutations and their propensity to be passed on to the next generation that led to the transition from wolf to a dog and then the development of such drastically different dog breeds.
Genomes and Genomic Testing
Genomes are basically a map of the genes contained on a DNA strand. They tag the normal location of each gene. Creating a genome for a species used to be a time-consuming and labor-intensive process but new technology and a better understanding of genetics have made it much quicker and simpler.
The entire genomic sequence for all 39 pairs of chromosomes found in dogs has been mapped. Using this as a guide, scientists are able to find the exact genes responsible for certain genetic mutations in dogs as well as many other species, including human beings.
Using this information, it may someday be possible to cure ailments and illnesses caused by genetic mutations and perhaps even prevent them from happening at all. For now, genomic testing, or the testing of a strand of DNA for genes that are out of place, missing, or doubled up, is useful to prevent the breeding of dogs with recognized mutations. These days, there are home dog DNA test kits available to pet owners.
The next step in the genomes to figure out what each gene in the sequence does. Remember that each gene is responsible for the presence or absence of a specific trait. Sometimes they work alone and sometimes multiple genes work together to define the parameters of a given trait. By learning which trait or traits each gene or group of genes is responsible for, we can not only predict the outcome of a breeding pair but perhaps also determine it.
There is also work being done on removing specific genes or sequences of genes and replacing them with other genes. While this may bring to mind the terrors of The Island of Doctor Moreau, where the genetics of different species, including humans were spliced together to create horrendous monsters, the actual work being done is much less scary.
This work, known as genetic modification, is being used to create things like drought-resistant crops and mice with certain diseases. While many people fear the possibilities that arise from genetic modification, it has the possibility to significantly improve the lives of both humans and animals around the world.
Recessive and Dominant Genes
Most genes can be described as either recessive or dominant. These terms are used to describe how they react when paired with one another when the two chromosomes merge to form a zygote. As the name suggests, dominant genes win out in pairings that have both dominant and recessive genes. This means that the coding from information from the dominant gene is the coding that the cells receive and respond to. The information from the recessive gene is hidden or masked and cannot be seen in the offspring.
Recessive genes are only expressed if both parents pass them on to their offspring. For example, blue eyes in humans are a recessive trait. You can’t have a child born with blue eyes if both parents haven’t donated the gene for it to the zygote. However, a parent may carry the gene for blue eyes that have been masked by the dominant gene for brown eyes and still pass the blue eye gene on. This means that it is possible, although statistically unlikely, for two people who have brown eyes to have a child that has blue eyes if both parents passed on the recessive gene for it.
Best Breeding Practices are Vital
Many of the genetic mutations that negatively affect the offspring are recessive in nature meaning that both parents have to carry the damaged gene for it to be expressed in the offspring. This is why breeding programs for purebred dogs have to be so careful about choosing mating partners that are not closely related. Dogs, or any animals, that are closely related are more likely to carry the same genes. This makes it more likely that a recessive gene will partner with another recessive gene, thus allowing the coding from that gene to be expressed, or sent on, to direct the cells’ actions.
Irresponsible breeding practices are what lead to the negative trends that are sometimes seen in purebred dogs. Things like hip dysplasia in German Shepherds and skittish and aggressive behavior in Doberman Pinschers are the direct result of breeders frequently using related dogs for breeding. Once a recessive trait has become prevalent in a closed community, like purebred dogs, it is very hard to find individual animals that do not carry the negative trait for breeding purposes, especially if it is one that does not show its effect until after a dog has reached breeding age.
Breeding practices that allow negative recessive genes to become prevalent can be devastating to a breed of dogs. Once that gene has become widespread in a population it is very difficult to remove it without introducing DNA from other breeds of dogs. This, of course, results in a puppy that is no longer considered a purebred dog.
The prevalence of recessive genes in purebred dog populations is why mixed breed dogs tend to have longer, healthier lives. It also explains the new popularity of hybrid dogs, like Labradoodles or Yorkipoos. By combining the genetics of two different purebred breeds you significantly lessen the chances of negative recessive traits being expressed while still maintaining the favorable characteristics of both breeds.
Combatting negative genetic traits is one of the most promising aspects of genomic testing. Testing young dogs for the presence of these recessive genes, whether they are expressed or not allows breeders to make informed decisions about their breeding animals.
Every trait that your dog possesses is a direct result of what is contained in those 39 pairs of chromosomes. While you may never be able to actually see those chromosomes or the DNA and genes they contain, their effects will determine your dog’s appearance, behavior, health, and longevity. If you choose to own a purebred dog, only buy from reputable breeders. This will not only improve the quality of life for your dog but also help to protect the breed itself from being degraded by irresponsible breeders that do not respect those 78 chromosomes.