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UNIT 3: GENETICS AND ANIMAL BREEDING OBJECTIVES 3.1 Define Terms 3.2 Discuss Mendel’s contributions to the study of genetics 3.3 Identify the parts of and explain the functions of cells, chromosomes, and genes 3.4 Differentiate between genotype and phenotype 3.5 Compare purebred breeding and crossbreeding OBJECTIVES 3.6 Identify factors to consider in selecting breeding animals 3.7 Describe reproduction processes in agricultural animals 3.8 Explain artificial insemination and identify its advantages and disadvantages 3.9 Discuss genetic engineering and its effect on animal agriculture 3.1 DEFINE TERMS 1. cell—the basic unit of life 2. chromosome—a strand of genetic material that contains genetic code 3. crossbreeding—the breeding of two different pure breeds 4. gene—a unit of inheritance composed of DNA 3.1 DEFINE TERMS 5. genetics—the study of heredity 6. genotype—genetic makeup of an animal 7. heredity—the passing of traits from parents to offspring 8. phenotype—the outward expression of a gene 3.1 DEFINE TERMS 9. purebred breeding—the breeding of animals within the same breed 10. reproduction—the process by which new organisms are derived normally involving the union of the male and female sex cells 3.2 DISCUSS MENDEL’S CONTRIBUTIONS TO THE STUDY OF GENETICS WHY IS AN UNDERSTANDING OF GENETICS IMPORTANT, AND WHAT WAS THE IMPACT OF GREGOR MENDEL’S DEVELOPMENT OF THE BASIC PRINCIPLES OF HEREDITY? Genetics is the study of the laws and processes of biological inheritance. A. The study of genetics is concerned with the transfer of traits. 1. Gregor Mendel discovered that these traits are inherited through units called genes. WHY IS AN UNDERSTANDING OF GENETICS IMPORTANT, AND WHAT WAS THE IMPACT OF GREGOR MENDEL’S DEVELOPMENT OF THE BASIC PRINCIPLES OF HEREDITY? 2. Mendel further discovered that genes were found in pairs, with half of the inherited traits coming from the father and half from the mother. This passing of traits from parents to offspring is called heredity. 3. Not all differences in animals are caused by genetics. Some are caused by the environment, or the conditions in which the animal is raised. WHY IS AN UNDERSTANDING OF GENETICS IMPORTANT, AND WHAT WAS THE IMPACT OF GREGOR MENDEL’S DEVELOPMENT OF THE BASIC PRINCIPLES OF HEREDITY? B. A chromosome is a tiny, threadlike part in a cell that contains the genetic material. 1. Chromosomes are found in the nucleus of cells. The genetic material found in the chromosomes is called the genome of the organism. When animals mate, the genome of the offspring is a combination of the traits from the mother and the father. WHY IS AN UNDERSTANDING OF GENETICS IMPORTANT, AND WHAT WAS THE IMPACT OF GREGOR MENDEL’S DEVELOPMENT OF THE BASIC PRINCIPLES OF HEREDITY? 2. All the cells within the animal are genetically identical. Each cell contains identical numbers of chromosomes. The number found in a cell varies between species. 3. Chromosomes are made of DNA, or deoxyribonucleic acid, which contains genes. DNA is a protein-like nucleic acid that controls inheritance. WHY IS AN UNDERSTANDING OF GENETICS IMPORTANT, AND WHAT WAS THE IMPACT OF GREGOR MENDEL’S DEVELOPMENT OF THE BASIC PRINCIPLES OF HEREDITY? 4. Each DNA molecule consists of two strands shaped as a double helix, or spiral structure. These strands are nucleotides bonded together by pairs of nitrogen bases. The nucleotides are made up of sugar molecules held together by phosphates. There are four nitrogen bases found in DNA: cytosine, guanine, adenine, and thymine. WHY IS AN UNDERSTANDING OF GENETICS IMPORTANT, AND WHAT WAS THE IMPACT OF GREGOR MENDEL’S DEVELOPMENT OF THE BASIC PRINCIPLES OF HEREDITY? 5. The genetic code is the sequence of nitrogen bases in the DNA molecule. This sequence code is for amino acids and proteins. The ability of DNA to replicate itself allows for the molecule to pass genetic information from one cell generation to the next. 3.3 IDENTIFY THE PARTS OF AND EXPLAIN THE FUNCTIONS OF CELLS, CHROMOSOMES, AND GENES WHAT ARE THE PARTS OF AN ANIMAL CELL, AND WHAT ARE THE FUNCTIONS OF THOSE PARTS? Cells of all organisms have the same basic makeup, or structure. Differences do occur, however, between the cells of plants and animals. A. Animal cell components: 1. The cell membrane is the outside covering of the cell. It is made of a thin layer of lipids (fats). The functions of the cell membrane are: WHAT ARE THE PARTS OF AN ANIMAL CELL, AND WHAT ARE THE FUNCTIONS OF THOSE PARTS? a. To separate the cell contents from the external environment. b. To allow raw materials (carbohydrates and proteins) to enter the cell. c. To allow newly made proteins and waste to exit the cell. WHAT ARE THE PARTS OF AN ANIMAL CELL, AND WHAT ARE THE FUNCTIONS OF THOSE PARTS? 2. The nucleus is the “brain” of the cell. The nucleus controls all the cell’s activity. It is surrounded by the nuclear membrane, which functions similarly to the cell membrane. The nucleus also contains chromosomes, which are small strands of genetic material. WHAT ARE THE PARTS OF AN ANIMAL CELL, AND WHAT ARE THE FUNCTIONS OF THOSE PARTS? 3. Cytoplasm is a jellylike substance between the cell membrane and the nuclear membrane. It contains several specialized structures called organelles. a. The endoplasmic reticulum is a network of membranes that connects the cell membrane to the nucleus. There are two sections of the endoplasmic reticulum. Each section has its own function. WHAT ARE THE PARTS OF AN ANIMAL CELL, AND WHAT ARE THE FUNCTIONS OF THOSE PARTS? (1) The smooth endoplasmic reticulum is the site for the production of lipids (fats) and hormones. (2) The rough endoplasmic reticulum is the site for the production of proteins. WHAT ARE THE PARTS OF AN ANIMAL CELL, AND WHAT ARE THE FUNCTIONS OF THOSE PARTS? b. Mitochondria are small, egg-shaped organelles that manufacture adenosine triphosphate (ATP). ATP is used as an energy source for the cell. It converts food into energy through cellular respiration. c. Lysosomes are round organelles that cause the digestion of proteins through the release of enzymes. These are made by the Golgi apparatus. WHAT ARE THE PARTS OF AN ANIMAL CELL, AND WHAT ARE THE FUNCTIONS OF THOSE PARTS? d. The Golgi apparatus consists of flattened membrane sacs that receive substances transported from the endoplasmic reticulum. It also stores the substances and alters their chemical structure. 3.4 DIFFERENTIATE BETWEEN GENOTYPE AND PHENOTYPE HOW DO WE PREDICT THE GENOTYPES AND PHENOTYPES FROM MONOHYBRID AND DIHYBRID CROSSES BY USING THE PUNNETT SQUARE? Resulting offspring of reproduction have both genotype and phenotype heredity. A. Genotype is the actual genetic code. It controls physical and performance traits. The genotype of an organism cannot be changed by environmental factors. HOW DO WE PREDICT THE GENOTYPES AND PHENOTYPES FROM MONOHYBRID AND DIHYBRID CROSSES BY USING THE PUNNETT SQUARE? B. Phenotype is the organism’s physical or outward appearance. This is the part of the genotype the organism expresses or shows. In some instances, phenotype may be altered by the environment. organism’s HOW DO WE PREDICT THE GENOTYPES AND PHENOTYPES FROM MONOHYBRID AND DIHYBRID CROSSES BY USING THE PUNNETT SQUARE? C. A homozygous organism is one having similar alleles, or genes, on the DNA molecule for a particular trait, while a heterozygous organism is one having different alleles for a particular trait. D. The Punnett square is a useful tool to help determine both the genotype and phenotype from animal crosses. 3.5 COMPARE PUREBRED BREEDING AND CROSSBREEDING WHAT ARE SOME OF THE COMMON BREEDING SYSTEMS USED IN LIVESTOCK PRODUCTION? The system of breeding to be used by a producer depends on the kind of livestock operation. There are two basic systems of breeding used in livestock production, and there are several variations of each system available for producers to utilize. The two basic systems are straightbreeding and crossbreeding. WHAT ARE SOME OF THE COMMON BREEDING SYSTEMS USED IN LIVESTOCK PRODUCTION? A. Straightbreeding is mating animals of the same breed. There are several variations of this system. Some of the most common are purebred breeding, inbreeding, outcrossing, and grading up. WHAT ARE SOME OF THE COMMON BREEDING SYSTEMS USED IN LIVESTOCK PRODUCTION? 1. A purebred animal is an animal of a breed. Both parents of the animal must have been purebred. The production of purebred animals is a specialized business. These animals provide the foundation stock for crossbreeding to produce market animals. WHAT ARE SOME OF THE COMMON BREEDING SYSTEMS USED IN LIVESTOCK PRODUCTION? 2. Inbreeding is the mating of related animals. This increases the genetic purity of the stock produced. The pairing of the same genes is increased, and offspring become more genetically homozygous. There are two types of inbreeding. WHAT ARE SOME OF THE COMMON BREEDING SYSTEMS USED IN LIVESTOCK PRODUCTION? a. Closebreeding is the most intensive form of inbreeding, in which the animals being mated are very closely related and can be traced back to more than one common ancestor. b. Linebreeding refers to mating animals that are more distantly related and can be traced back to just one common ancestor. WHAT ARE SOME OF THE COMMON BREEDING SYSTEMS USED IN LIVESTOCK PRODUCTION? 3. Outcrossing is the mating of animals of different families within the same breed. The purpose of outcrossing is to bring into the breeding program traits that are desirable but not present in the original animals. 4. Grading up is the mating of purebred sires to grade females. A grade animal is any animal not eligible for registry as a purebred. This is done as a less-expensive way to improve the quality of animals on a farm or ranch. WHAT ARE SOME OF THE COMMON BREEDING SYSTEMS USED IN LIVESTOCK PRODUCTION? B. Crossbreeding is the mating of two animals from different breeds. The resulting offspring is a hybrid. This generally results in improved traits in the offspring. Superior traits that result from crossbreeding are called hybrid vigor or heterosis. 3.6 IDENTIFY FACTORS TO CONSIDER IN SELECTING BREEDING ANIMALS WHAT IS AN EPD? EPD stands for Expected Progeny Difference. It is the measure of the degree of difference between progeny of the bull and the progeny of the average bull of the breed the trait is being measured from. EPD EXAMPLE COMMON EPD TITLES BW (Birth Weight) WW (Weaning Weight) YW (Yearling Weight) MILK CE (Calving Ease) CED (Calving Ease Direct) Predicts calving ease of a sire when mated to heifers. CW (Carcass Weight) DOC (Docility) MW (Mature Weight) MH (Mature Height) BOVINE ELITE EPD Comparison 3.7 DESCRIBE REPRODUCTION PROCESSES IN AGRICULTURAL ANIMALS WHAT ARE THE MAJOR REPRODUCTIVE ORGANS IN MALE MAMMALS? WHAT ARE THE FUNCTIONS OF THOSE ORGANS? To have a successful livestock operation, a producer must have an understanding of the various reproductive organs and their functions. In most cases, a livestock operation will have only a limited number of males available for breeding. The male reproductive system contains several interconnected parts that must all work together for successful mating. WHAT ARE THE MAJOR REPRODUCTIVE ORGANS IN MALE MAMMALS? WHAT ARE THE FUNCTIONS OF THOSE ORGANS? Some of the major organs found in the male mammal reproductive system are: A. Testicles—The testicles produce sperm, the male sex cells (also called spermatozoa). They also produce a hormone called testosterone that causes the appearance and behavior of the animal to be masculine. Two testicles are present in male mammals. WHAT ARE THE MAJOR REPRODUCTIVE ORGANS IN MALE MAMMALS? WHAT ARE THE FUNCTIONS OF THOSE ORGANS? B. Epididymis—The epididymis is the storage site for sperm cells. From the testicle, cells enter the mature. Sperm can fertilize a female’s ova (female sex cell) as it travels through the epididymis. A separate epididymis is attached to each testicle. these epididymis to WHAT ARE THE MAJOR REPRODUCTIVE ORGANS IN MALE MAMMALS? WHAT ARE THE FUNCTIONS OF THOSE ORGANS? C. Scrotum—The scrotum is a two-lobed sac that contains and protects the two testicles. It also regulates the temperature of the testicles, which is lower than the body temperature. When the environment temperature is low, the scrotum contracts, pulling the testicles toward the body and its warmth. WHAT ARE THE MAJOR REPRODUCTIVE ORGANS IN MALE MAMMALS? WHAT ARE THE FUNCTIONS OF THOSE ORGANS? When the environmental temperature is high, the scrotum relaxes, permitting the testicles to drop away from the body. Maintaining the correct temperature is critical because extreme temperatures (too hot or too cold) can affect the production and vitality of sperm. WHAT ARE THE MAJOR REPRODUCTIVE ORGANS IN MALE MAMMALS? WHAT ARE THE FUNCTIONS OF THOSE ORGANS? D. Vas deferens—The vas deferens is essentially a transportation tube that carries the sperm-containing fluid from each epididymis to the urethra. E. Urethra—The urethra is a large, muscular canal extending from the urinary bladder. Both semen and urine move through the urethra to the end of the penis. WHAT ARE THE MAJOR REPRODUCTIVE ORGANS IN MALE MAMMALS? WHAT ARE THE FUNCTIONS OF THOSE ORGANS? F. Accessory sex glands—These are several glands that add volume and nutrition to the sperm-rich fluid coming from the epididymis. G. Seminal vesicles—The seminal vesicles open into the urethra. They produce a fluid that protects and transports the sperm. H. Prostate gland—The prostate gland is near the urethra and the bladder. It produces a fluid that is mixed with the seminal fluid. WHAT ARE THE MAJOR REPRODUCTIVE ORGANS IN MALE MAMMALS? WHAT ARE THE FUNCTIONS OF THOSE ORGANS? I. Cowper’s gland—The cowper’s gland produces a fluid that moves down the urethra ahead of the seminal fluid. This fluid cleans and neutralizes the urethra, which helps protect the sperm as they move through the urethra. The mixture of the seminal and prostate fluid and the sperm is called semen. WHAT ARE THE MAJOR REPRODUCTIVE ORGANS IN MALE MAMMALS? WHAT ARE THE FUNCTIONS OF THOSE ORGANS? J. Penis—The penis deposits the semen within the female reproductive system. The urethra in the penis is surrounded by spongy tissue that fills with blood when the male is sexually aroused, which causes an erection that is necessary for copulation (mating) to occur. The sigmoid flexure (found in bulls, rams, and boars) and the retractor muscle extend the penis from the sheath, which is a tubular fold of skin. Horses and other mammals do not have a sigmoid flexure. WHAT ARE THE MAJOR REPRODUCTIVE ORGANS IN FEMALE MAMMALS? WHAT ARE THE FUNCTIONS OF THOSE ORGANS? Like males, female mammals have a complex system of organs that compose the reproductive system. It is important that those interested in animal production be familiar with these various organs and their functions. Some of the major organs that compose the female reproductive tract are: WHAT ARE THE MAJOR REPRODUCTIVE ORGANS IN FEMALE MAMMALS? WHAT ARE THE FUNCTIONS OF THOSE ORGANS? A. Ovary—The ovary produces female gametes, which are sex cells that can unite with other sex cells. These are called ova (eggs). A female mammal will typically have two ovaries, which also produce the female sex hormones: estrogen and progesterone. Within each ovary, there are hundreds of tiny follicles or cavities. The ova are produced in the follicles. Each ovum is the largest single cell in the body. WHAT ARE THE MAJOR REPRODUCTIVE ORGANS IN FEMALE MAMMALS? WHAT ARE THE FUNCTIONS OF THOSE ORGANS? B. Oviducts—The oviducts are two tubes that carry the ova from the ovaries to the uterus. The oviducts are also called the fallopian tubes. The oviducts are close, but they are not attached to the ovaries. The funnel-shaped end of each oviduct that is close to the ovary is the infundibulum. At ovulation the follicle ruptures, releasing an ovum that is caught by the infundibulum. WHAT ARE THE MAJOR REPRODUCTIVE ORGANS IN FEMALE MAMMALS? WHAT ARE THE FUNCTIONS OF THOSE ORGANS? After copulation, sperm move through the uterus to the oviduct. Fertilization of the ovum occurs in the upper end of the oviduct. The zygote, or fertilized egg cell, moves to the uterus about two to four days after fertilization. WHAT ARE THE MAJOR REPRODUCTIVE ORGANS IN FEMALE MAMMALS? WHAT ARE THE FUNCTIONS OF THOSE ORGANS? C. Uterus—The uterus of mammals is a Yshaped structure consisting of the body, two uterine horns, and the cervix. The size and shape of the uterus varies among mammals. The upper part of the uterus consists of the two uterine horns that develop into the oviducts or fallopian tubes. WHAT ARE THE MAJOR REPRODUCTIVE ORGANS IN FEMALE MAMMALS? WHAT ARE THE FUNCTIONS OF THOSE ORGANS? Mammals that normally produce large numbers of offspring at each breeding have relatively large horns and a small body. Those mammals that normally produce single offspring or twins have smaller horns and a larger body. In most mammals, pregnancy normally occurs in the uterine horns. In horses, however, pregnancy normally occurs in the body of the uterus. WHAT ARE THE MAJOR REPRODUCTIVE ORGANS IN FEMALE MAMMALS? WHAT ARE THE FUNCTIONS OF THOSE ORGANS? In all mammals, the fetus grows within the uterus, where it remains until parturition or birth. The cervix is the lower outlet of the uterus and is composed primarily of connective tissue that constitutes the gateway between the uterus and the vagina. Like the rest of the reproductive tract, the cervix is lined with mucosal cells. These cells make significant changes as the animal goes from one estrous cycle to another and during gestation or pregnancy. WHAT ARE THE MAJOR REPRODUCTIVE ORGANS IN FEMALE MAMMALS? WHAT ARE THE FUNCTIONS OF THOSE ORGANS? D. Vagina—The vagina serves as the female organ of copulation at mating and as the birth canal at parturition. It is the passage between the cervix and the vulva. The lining is moist during estrus and dry when the animal is not in estrus. WHAT ARE THE MAJOR REPRODUCTIVE ORGANS IN FEMALE MAMMALS? WHAT ARE THE FUNCTIONS OF THOSE ORGANS? E. Bladder—The bladder collects the liquid waste, which is called urine. The urine passes through the urethra to the vagina. The urethra attaches to the floor of the vagina between the cervix and the vulva. The bladder is not considered part of the reproductive tract in females. WHAT ARE THE MAJOR REPRODUCTIVE ORGANS IN FEMALE MAMMALS? WHAT ARE THE FUNCTIONS OF THOSE ORGANS? F. Vulva—The vulva is the external opening of the reproductive and urinary systems. The exterior and visible part of the vulva consists of two folds called the labia majora. The labia minora are two folds located just inside the labia majora. WHAT ARE THE MAJOR REPRODUCTIVE ORGANS IN FEMALE MAMMALS? WHAT ARE THE FUNCTIONS OF THOSE ORGANS? G. Clitoris—The clitoris is the sensory and erectile organ of the female. It is located just inside the vulva. The clitoris develops from the same embryonic tissue as the penis in the male and produces sexual stimulation during copulation. 3.8 EXPLAIN ARTIFICIAL INSEMINATION AND IDENTIFY ITS ADVANTAGES AND DISADVANTAGES WHAT ARE THE STEPS INVOLVED IN ARTIFICIAL INSEMINATION? Artificial insemination is the placing of semen in the female reproductive tract by artificial techniques. The use of this technique has increased over the past several years due to advancements in technology. The process varies by species, but it typically involves specialized equipment and a trained technician. WHAT ARE THE STEPS INVOLVED IN ARTIFICIAL INSEMINATION? The technician deposits a prepared unit of semen into the reproductive tract of the female at a predetermined time. The objective of artificial insemination is to deposit the semen at the appropriate time to achieve fertilization. Timing varies by species of animal and should be closely studied prior to implementing artificial insemination. WHAT ARE THE STEPS INVOLVED IN ARTIFICIAL INSEMINATION? There are several different segments that support the process of artificial insemination. Some of the major segments include: A. Semen collection—Artificial insemination requires that semen be collected from the male. Semen may be collected via manual stimulation or the use of an artificial vagina. The technique used depends on the species from which the semen is being collected. WHAT ARE THE STEPS INVOLVED IN ARTIFICIAL INSEMINATION? Manual stimulation involves the use of an electronic probe to encourage ejaculation. While this process produces a semen sample, it has been determined that a more appropriate sample can be collected if the male is stimulated. This can be achieved by utilizing an artificial vagina. It involves allowing the male to mount a dummy animal and inserting the penis into an artificial vagina. This process more closely simulates naturally breeding, resulting in a higher quality semen sample. WHAT ARE THE STEPS INVOLVED IN ARTIFICIAL INSEMINATION? B. Semen evaluation—After semen is collected from the male, it is evaluated for quality. Only the highest quality semen is utilized for artificial insemination. The semen must be evaluated under a microscope to verify that it contains an appropriate number of living sperm cells. If approved for use, the sperm is then processed to increase utilization. WHAT ARE THE STEPS INVOLVED IN ARTIFICIAL INSEMINATION? C. Semen extension—Semen is extended during the processing phase, which allows for a single collection to be divided into many units. Only one unit is required for artificial insemination; by extending it, the semen can be used for several breedings. To extend semen, specialized compounds are added to enhance the viability and storage of the sperm cells. Depending on the species, often nutrients are added to expand the mass of each semen unit. WHAT ARE THE STEPS INVOLVED IN ARTIFICIAL INSEMINATION? D. Semen storage—Semen is stored in one of two ways. It is either frozen to extremely low temperatures or maintained fresh until use. How semen is stored depends on the species. For example, cattle semen is slowly cooled and frozen at a temperature of –320°F (– 196°C). Liquid nitrogen is used to obtain these extreme temperatures. WHAT ARE THE STEPS INVOLVED IN ARTIFICIAL INSEMINATION? Properly frozen and stored semen can remain viable and be used 30 to 40 years later. The frozen semen is thawed prior to use in a 95 to 98°F (33 to 34°C) water bath. It is then ready to be deposited in the female. Fresh semen cannot be stored for such long periods of time. For example, collections from pigs are kept at approximately 60°F (16°C) for two to four days. Fresh semen becomes less fertile over time, so immediate use improves the chances of successful insemination. WHAT ARE THE STEPS INVOLVED IN ARTIFICIAL INSEMINATION? 3.9 DISCUSS GENETIC ENGINEERING AND ITS EFFECT ON ANIMAL AGRICULTURE WHAT IS GENETIC ENGINEERING, AND WHAT ARE THE STEPS OF RECOMBINANT DNA TECHNOLOGY? A. Genetic engineering is a form of biotechnology in which genetic information is changed to make a new product. Through this process, sections of the DNA strand are cut out, and new sections are inserted. Gene transfer is the moving of a gene from one organism to another. Genetic engineering is a means of complementing traditional breeding programs. WHAT IS GENETIC ENGINEERING, AND WHAT ARE THE STEPS OF RECOMBINANT DNA TECHNOLOGY? B. Recombinant DNA is gene slicing. Genes are cut out of a DNA strand with a restriction enzyme that works like a scalpel. The genes are then inserted into circular DNA molecules in bacteria plasmids. Plasmids are circular pieces of DNA found outside the nucleus in bacteria. The plasmid is inserted into the cell that is to be altered, which allows the DNA of two different organisms to be combined. Recombinant DNA is a very complicated and complex procedure. Most cells die in the process. Many surviving cells do not have the new DNA present in the nucleus. REVIEW 3.1 Define Terms 3.2 Discuss Mendel’s contributions to the study of genetics 3.3 Identify the parts of and explain the functions of cells, chromosomes, and genes 3.4 Differentiate between genotype and phenotype 3.5 Compare purebred breeding and crossbreeding REVIEW 3.6 Identify factors to consider in selecting breeding animals 3.7 Describe reproduction processes in agricultural animals 3.8 Explain artificial insemination and identify its advantages and disadvantages 3.9 Discuss genetic engineering and its effect on animal agriculture