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Horse Genetics Nature ordained that _____________ be applied to horse breeding long before there were geneticists. Prior to the domestication of horses, there was __________ _______ for speed and stamina. One of the most important defense mechanisms of the horse was to outrun its enemies. Natural selection was probably very effective in improving speed and endurance, since the slower horses were eliminated by predators. Horse Genetics Many horse _______ have been _________ genetics as they concern themselves with the are of ________. Their guiding concept of heredity is that “like begets like”. Breeders in the 18th century made a tremendous contribution pointing the way toward horse ________ before Mendel’s _______ became known to the world. As knowledge of genetics developed, there ________ an understanding of the science that underlies the art of horse breeding. Horse Genetics Genetics The _________ of animals are made up of millions or even billions of _________ cells. Each cell contains a __________ in which there are a number of pairs of bundles called _____________. In turn, the chromosomes carry ________ of minute particles called ________, which are the basic hereditary material. The nucleus of each cell of a horse contains ____ pairs of chromosomes, or a total of _____. Horse Genetics Genetics There are _______ of pairs of genes on each chromosome. Genes determine all the ________ characteristics of animals from the _____ type to the _____ of the hair. The mule has an ______ number of chromosomes and cannot __________. The ________ of an animal refers to the specific genes it possesses on its chromosomes. __________ describes the complete set of “instructions” for making an organism. Horse Genetics Genetics __________ gene expression has a full allele effect. An example would be when a gray horse produces a gray horse. ___________ character appears only when both members of a pair of alleles are alike. The job of __________ qualities from one _________ to the next is performed by the gene cells- a _______ from the male and an ______, or ______ from the female. Horse Genetics Genetics There are alternate forms of each gene. The _______ gene forms are referred to as alleles. If the alleles are the same, the condition is referred to as ___________. If the alleles are different, the condition is called ___________. _________ and ____________ are the tools through which the horse breeder may obtain stallions and mares whose chromosomes and genes contain ____________ hereditary determiners-animals that are genetically more homozygous. Horse Genetics Genetics Gene changes are known as ________. A mutation may be defined as a _________ variation that is later passed on through ____________ and that results from changes in a gene or genes. Horse Genetics Simple Gene Inheritance (Qualitative Traits) In the simplest type of inheritance only _____ pair of genes is involved. Thus, a _______ of genes may be ________ for the color of body hair in horses. The idea that certain basic colors may have a rather ______ explanation of inheritance should not alter the fact that other genes may play an important role through their ___________ on basic schemes. The possible gene ____________ are governed by the laws of chance. Horse Genetics Simple Gene Inheritance (___________________) Other possible examples of _________ gene inheritance in horses might include _____ color and the set of the ears on the head. Horse Genetics Dominant and Recessive Alleles A dominant ___________ may cover up a recessive allele. Therefore, a horse’s breeding ____________ cannot be recognized by its _______________ (how it looks). ____________ genes can be passed on from generation to generation, _____________ only when ______ animals, both of which carry the same recessive allele, happen to mate. Horse Genetics Dominant and Recessive Alleles Reputable breeders have an obligation, not only to themselves, but to their customers. Purebred animals must be __________ of _________ genes by ___________ those stallions and mares that are known to have transmitted the undesirable recessive gene. Horse Genetics Incomplete Dominance In some cases, dominance is neither __________ nor _____________, but __________ or ___________ and expresses in a variety of ways. Perhaps the best known case of this type in horses is the ____________ color. Genetic studies of the Palomino indicate that the color is probably ___________- that it cannot be made _______ breeding, no matter how long or how persistent the effort. Horse Genetics Multiple Gene Inheritance (Quantitative Traits) Important characters such as speed are due to many genes; thus, they are called _________-__________ characters. _____________ inheritance refers to the ________ to which a characteristic is __________. For example, all Thoroughbred horses can run and all inherit some ability to run, but it is the degree to which they inherit the ability that is important. In quantitative inheritance, the extremes (either good or bad) tend to swing back to the average. Horse Genetics Horse Color Recent advances in ________ have allowed us to understand better how coat color is inherited, thus making it possible to plan __________ that will produce foals of a certain color. Horse Genetics Gene _______ Genetic __________ of black color restricted to the points of a horse is through gene A, or the A allele. The ______ allele is _________. A uniformly black horse has the ________ genotype ____. Horse Genetics Gene ___ Gene E, or the E allele, ________ the expression of black hair on the body. The _________ form _____, results in uniformly redcolored horses. The ____ gene is related to (and can mask) the A gene. Horse Genetics Gene ____ ________ coloring is due to the dominant gene _____. Any horses with the _____ allele will be ______; ___________ horses will have the genotype _______. Gray horses can be born ______ color. Horse Genetics Gene _______ Solid ________ coloring is controlled by gene _____. The __________ homozygous (______) condition is ________; thus, all white horses have the genotype. All non-white horses have the genotype ______. Horse Genetics Gene ______ and _______ The ___ and ____ alleles are _______ alleles. Gene C affects only ______ pigment and causes the pigment to lighten. The C gene does not affect ________ pigment. Gene D _________ from gene C in that it can dilute both _______ and __________ pigment. With the D allele, _______ is diluted to a _______ or _________, and _________ is diluted to a yellow-tan. Horses with the D allele also show ________ marks such as the dorsal stripe, shoulder stripes, and leg barring. Horse Genetics Gene _____ The spotting of paint and pinto horses is controlled by the ___________ gene TO. The tobiano color pattern is _________; thus, __________ must have the genotype ________. Homozygous TOTO horses are _______ and are sought after by horse breeders for their ability to always produce _________foals. Genetic tests are available to determine whether a horse is homozygous. Horse Genetics Heritability of Performance Traits Relatively little scientific work has been done on the heritability of ___________ of horses- on the genetics of ________ ability, _________ ability, ________ ability, etc. The horse is the ______ farm animal to which the science of genetics has been added to the ______ of breeding. Differences in the performance ability (working, racing, jumping) are due to _______ major forces - _________ and _________. Horse Genetics Heritability of Performance Traits The important __________ factors in determining the _________ performance of horses are _________ (both prenatal and postnatal), _____ care, quality of ________, _______ of the handler, and _________. An important genetic ___________ is that traits as such are not inherited. The ability to respond to a _______ set of environmental conditions in order to produce a trait with a measurable effect is inherited. _________ estimates on the heritability of performance traits in horses are limited in comparison with those for other species. Horse Genetics The following conditions would tend to indicate a _____________ defect in horses: If the defect had previously been reported as hereditary in the same breed. If it occurred more frequently within certain families or when there had been inbreeding. If it occurred in more than one season and when different rations had been fed. Horse Genetics The following __________ might be accepted as indications that the abnormality was due to a ___________deficiency: If it had previously been reliably reported to be due to a nutritional deficiency. If it appeared to be restricted to a certain area. If it occurred when the ration of the dam was known to be deficient. If it disappeared when an improved ration was fed.