What types can dogs be divided into based on coat characteristics?
The dog's coat is an important skin derivative that protects the dog from adverse external environmental influences and maintains a constant body temperature. The form and color of the coat are important characteristics of dog breeds, and a gorgeous coat is a second life for many toy dogs.
The dog's coat consists of top hair, undercoat, and decorative hair. Top hair, also called outer hair, is the main part that constitutes the dog's coat color; it is generally long and coarse, with medullated hair making up the majority, and it mainly serves to keep the dog warm. Decorative hair refers to the hair growing on the ears, tail, and lower limbs that serves a decorative function. According to coat length, dogs are generally divided into short-haired dogs, hairless dogs, long-haired dogs, and silky-haired dogs.
(1) Short-haired dogs: such as the Shar-Pei, Greyhound, Boxer, Great Dane, Dalmatian, Egyptian Hound, and others. The short-haired trait in dogs is controlled by the dominant gene L. When a dog homozygous for gene L is crossed with a long-haired dog, the first generation all shows the short-haired trait, and only the second generation shows trait segregation, that is, a small number of long-haired dogs are produced.
(2) Hairless dogs: Generally speaking, hairless dogs are limited to abnormal offspring, but some dogs have this characteristic, such as the Chinese Crested Dog and the Mexican Hairless Dog. Under normal circumstances, these two breeds are not completely hairless; rather, hair grows only on areas such as the head, lower limbs, and tail. Research has shown that the hairless trait is controlled by the dominant H gene. When this gene is homozygous, it is lethal, so all living hairless dogs are heterozygotes Hh. Its inheritance pattern has sex-linked genetic characteristics, and most living hairless dogs are female. The Chinese Crested Dog has a history of more than 400 years and is also called the "Chinese Naked Dog." Its average weight is 5.5 kg, its height is 23-30 cm, its appearance resembles the Italian Greyhound, and its skin is pink or white, smooth, soft, and wrinkle-free. The Mexican Hairless Dog is similar in body size to the Chinese Crested Dog and has two types. The larger type is almost entirely limited to Mexico, where scholars strictly control its breeding; it weighs 11-16 kg and stands 40-51 cm tall. The smaller type is distributed outside Mexico, is petite, and has a more graceful build.
(3) Long-haired dogs: such as the straight-haired German Shepherd, the fringed-haired Rhodesian Ridgeback, the curly-haired English Setter and Cocker Spaniel, the heavily coated Old English Sheepdog, and the wire-haired Airedale Terrier, among others.
The long hair of long-haired dogs is controlled by the long-hair gene e and is inherited recessively, meaning that the long-haired trait appears only when this pair of genes is homozygous. Because the expression of gene e is affected by many factors, many long-haired types with different morphological characteristics are produced. Some dogs do not have very long coats, with hair lying flat over the body, limbs, and tail while still showing the long-haired trait, such as the English Setter; some dogs have coats that are thick and dense all over the body, such as the Chow Chow; some dogs have coats that are long and abundant, as well as coarse, thick, and fluffy, such as the Old English Sheepdog; some dogs have long coats with a wavy structure, such as the Cocker Spaniel and Poodle; some dogs do not have very long hair on the head, but the coat on other parts is very long, such as the Pekingese, Rough Collie, Shetland Sheepdog, Pomeranian, Japanese Chin, and Papillon; some dogs have both long hair and short hair, such as the Dachshund, Chihuahua, and St. Bernard.
(4) Silky-haired dogs: Many long-haired dogs in the world have coats that are soft and silky, such as the Japanese Chin, Maltese, and Papillon.