Dogs are descended from the grey wolf (Canis lupus) and were domesticated in Southeast Asia around 33,000 years ago ^[1][2][1,2]. Canine ancestors migrated alongside humans to Africa and the Middle East around 15,000 years ago, and then to Europe around 10,000 years ago [3].

Domestic dog breeds (Canis familiaris L.) were the earliest domesticated animals, with over 400 breeds around the world [4], and more than 150 being bred in Korea ^[5][6][5,6]. These dog breeds have evolved into a broad collection of breeds with diverse morphological and physiological features through domestication, and natural and artificial selection [1]. Some are stray dogs throughout the world, mostly in villages and cities near humans [7]. Domestication of a canine ancestor is very likely to have occurred during first settlements and early agriculture and is accepted as a first population bottleneck during which the size of genetic variation within the population was effectively reduced ^[8][9][8,9]. Regardless of the precise timeframe, it is undeniable that for many years, people have been selecting for certain behavioural traits such as peacefulness, agreeableness, non-aggressiveness, and loyalty, as well as physical characteristics such as coat colour, coat length, height, and facial appearance ^[10][11][10,11].

Dogs have evolved into one of the most common domestic species, as well as the most common carnivore. Their global population is estimated to be close to 900 million, and it is undoubtedly growing ^[12][13][12,13]. Modern dog breeds differ from other domesticated species due to the large amount of phenotypic variation caused by human selective desire [14], and because of their intelligence and behavioural abilities. The dog has evolved into hundreds of races with various variations, ranging from the Chihuahua’s height of a few tens of centimetres to the Irish Wolfhound’s height of more than one meter [15]. Thus, their appearance and behaviour are significantly different [16].

The development of a new generation of domestic dog breeds entirely dependent on genetic variation as observed through genetic differences within and between breeds [17]. However, the process of domestication has resulted in genetic bottlenecks, which have impacted the evolution of modern dog breeds [4]. Genetic bottlenecks are evolutionary events that cause a random decrease in the genetic variation, resulting in small founding populations and genetic drift [18]. The first bottleneck occurred >15,000 years ago during the domestication from the grey wolf ^[19][20][19,20]. The second bottleneck was caused by the isolation of the current dog breeds during the past >300 years, resulting in a smaller number of potential parents. The third bottleneck was from the use of popular sires after an intense selection for exterior traits [21].

Furthermore, most dog breeds are closed populations with no gene flow from outside, and only a small number of dogs are utilized for breeding ^[22][23][22,23], resulting in a loss of genetic diversity within and between breeds [24], and inbreeding with the occurrence of genetic defects and depression in fitness traits. Therefore, genetic variation management is necessary to prevent high levels of inbreeding, the loss of genetic diversity, and the emergence of genetic disorders in small populations [25].

2. The Importance of Keeping Dogs

The dog has been man’s faithful companion throughout history. They help with daily activities and make their families happy [26]. Dogs can be a source of comfort in times of emotional difficulty, as well as having positive psychological and physical health impacts [27]. Different behavioural responses, or temperaments, have resulted from the diversity of dog breeds, making dogs ideal for a variety of roles ranging from pets to working dogs. However, the owner’s expectations of the dog may differ from what the dog is required to provide [28]. It is, therefore, the owner’s responsibility to give appropriate care to the dog, and to realize that it is a descendant of the wolf and should have the possibility to show its natural behaviour. Some dogs are calm in nature, while others are aggressive, which changes their utility as they perform many roles for mankind [29]. Law enforcement uses service and working dogs to assist the police and military, while government agencies use them for a variety of purposes such as explosives and drug detection [30]. They were used for a wide range of purposes, including heading, pulling loads, therapy, sports activities, medical and genomics research, customs, rescue, security work, identifying biological material, companionship ^{[6][31][32][33][34]}[6,31,32,33,34], as a fighter, hunter, hauler, and source of food and fur [13]. Dogs are also used to help people with disabilities, such as guide dogs for the blind, seizure alert dogs, and hearing dogs ^[35][36][35,36]. People have also used dogs in specialty positions in which their superior sense of smell has been used to seek out termites, missing persons, and, in some instances, malignant tumours, due to their ability to learn and be directed by humans [11]. Ownership of a dog is likely to benefit the owner’s physical and mental health, including decreased depression, increased oxytocin levels, and lower blood pressure and cholesterol levels ^[37][38][37,38]. Dogs also encourage their owners to exercise on a regular basis, lowering the risk of cardiovascular disease for both parties [39]. Exercising with their owner is likely the primary source of exercise for a companion animal, and therefore it is strongly influenced by owner-related factors such as their physical and social environment, personal capabilities, interests, motivating factors for exercise, and relationship with their dog [40]. Dog owners promote social contact among themselves, which reduces feelings of loneliness [41]. Owning a dog has been shown to have positive psychological impacts, including less stress effects, a larger social communication network, and a high sympathetic ability and sense of mercy. Furthermore, people who live with dogs are less likely to become ill because of their gratifying life with the dog [42]. Companion animals are also ideal research subjects for investigating the genetic and environmental factors that influence human behaviour, personality, and psychiatric diseases [43]. Domestic dogs are important for many economic reasons [44]. Pet dogs are the driving force behind a multibillion sector that includes food production, veterinary care, specialty services, and, of course, dog breeding [45]. Breeding and selling dogs accounts for 5% of all dog-related income in Belgium and is a major source of employment [46]. However, because of genetic improvement, the focus of breeding shifted away from working ability and toward morphological characters (such as coat colour, texture, size, and skull shape) [28]. Consequently, this phenotypic selection of around 400 breeds is now regarded as the second bottleneck [28]. Therefore, conserving dogs with special abilities in these situations will preserve the genetics underlying them, allowing for their continued use and study [47]. The United Kingdom Kennel Club recognizes 215 dog breeds and separates them into seven divisions by function. Hound group hunting dogs are those that hunt by scent and sight. Gundog track (Pointers and Setters), hunt (Spaniels), and recover game (Retrievers). The terrier category consists of canines that were used to hunt vermin or foxes. Utility dogs were originally employed for working or guarding but are now largely companions. Working dogs were used for house guarding, and hunting. Pastorals herd and guard livestock [48]. Because of small body sizes, toy dogs are mostly kept as pets [48].