Printer Friendly

Chapter 3 Animal genetics and breeding.

Chapter Objectives

* Learn how traits are inherited

* Learn the major criteria to consider in the selection of breeding stock

* Learn about heritable diseases

GENETICS

All animals pass on traits to their offspring through their genes. These genes contain the information necessary for the formation of a new animal. To make genetic progress, animals with the most desirable traits must be mated. Selection is the process of deciding which animals should be allowed to reproduce and pass their genes to the next generation. Geneticists, scientists who study genetics, can use mathematical calculations to predict the outcome of a mating, or a set of matings within a herd. Many genes influence some desirable characteristics, such as speed in a racehorse; fewer genes control other characteristics, such as animal height. The fewer the genes that control a characteristic, the easier it is to alter that characteristic through selective breeding. Use of technologies such as artificial insemination and embryo transfer allow animal scientists to increase the genetic contribution of individual males and females that have the most desirable genes. Commonly used terms related to genetics are:

Allele (uh-lel) A certain form of a specific gene that is located in a particular position on the chromosome. Alleles are labeled by use of one letter. If both alleles on a chromosome are the same, they are indicated with the same letter (for example, BB or bb). If the alleles are different, they are labeled with upper- and lowercase letters (for example, Bb).

Aneuploid (ahn-u-ployd) An animal that has more or fewer chromosomes than an exact multiple of the monoploid number.

Animal breeding The scientific application of principles of genetics to improve a species. Artificial selection The human selection of animals for reproducing based on the traits we consider most desirable. In artificial selection, humans, not the animals or other factors, control the opportunities for reproduction.

Autosomes (aw-to-zo-m) All chromosomes other than sex chromosomes.

Breed A group of animals that has been selected to have a specific set of characteristics that differentiates them from other members of the species. Breeds typically have visible qualities known as breed characteristics that are common among all members. Different breeds can be bred and result in viable offspring that are referred to as crossbreds.

Carrier An animal that carries a gene but does not express the gene. This term is often used in relation to genetic diseases and defects.

Centromere (sehn-tro-mer) The part of a chromosome where the spindle fibers attach during division.

Chromosome (kro-mo-som) A large molecule containing the genes of a living thing.Chromosomes are paired in most cells (see Table 3-1).

Codominance (ko-dohm-i-nahns) When different alleles are located at one loci, but neither is dominant to the other. The phenotype reflects a combination of traits from both alleles, in a similar form to how they are seen in a homozygous state.

Crossbreeding A form of outcrossing where animals of different breeds within a species are crossed. Crossbreeding maximizes heterozygosity in the offspring. This can be a benefit or a negative, depending on the goals of the breeder. For example, a dog that is the result of crossbreeding would be less likely to have a genetic disease associated with either parent; however, it would be less representative of the breed of either parent.

Deoxyribonucleic acid (DNA) (de-ohck-se-ri-bo-nu-kle-ihck ah-sihd) The complex molecule that has all of the genetic information of a living thing. DNA is the "code" that determines all aspects of an organism's physical characteristics.

Dilution gene A gene that affects the expression of another color gene. For example, in horses, the dilution of the chestnut coat color results in a palomino horse.

Diploid (dihp-loyd) Cells containing two sets of chromosomes. Most cells are diploid cells.

Dominant (dohm-i-nahnt) An allele that is expressed completely over the other allele in the pair, and completely masks the other allele. If an allele is dominant, it is labeled with an uppercase letter (for example, B).

Epistasis (eh-pihs-tah-sihs) One gene or allele affecting the expression of another gene somewhere else on the chromosome.

Expression The degree to which a particular gene, or set of genes, influences an animal. Some genes are recessive, and are not expressed at all. Some genes are dominant, and completely mask other genes.

Fancier (fahn-se-er) A breeder who is interested in a specific breed of animal, and works toward the development and improvement of that breed. Often known by the species of the animal (for example, dog fancier, cat fancier, Angus fancier).

Foundation stock An animal, or animals, identified as the genetic basis of the breed. The majority of animals in a breed will be descended from foundation stock.

Gamete (gahm-et) Sex cells (sperm for males; ovum for females).

Gametogenesis (gahm-e-to-jehn-eh-sihs) The process of forming gametes.

Gene (jen) A unit of a chromosome that determines the characteristics an animal may have. Genes affect not only the physical traits we see, but also the production of proteins that control all functions and activities in the body. In many cases, numerous genes work together to impact what we see as one trait. The more genes that control one trait, the more difficult to change that trait.

Gene frequency How often a particular gene at a specific location occurs in a population. The population can be the population on a particular operation, or the population of a breed or species as a whole. Breeders that focus their matings on particular characteristics can increase the frequency of genes creating their desired result in their population of animals.

Gene pool The full assortment of genetic options available for the breeder, relative to the genetic differences in animals, not the number of animals. In species that are endangered, the gene pool is quite small.

Gene splicing Inserting new genetic material into a plasmid.

Gene transfer Moving a gene from one animal to another.

Genetic drift Changes in the genetic makeup of a population that are not the result of planned breeding, but are the result of random chance. For example, changes in the genes of a wild pig population would be due to genetic drift, since the breeding process is under no external control.

Genetic engineering A broad term to describe a variety of methods of moving genes between animals.

Genetic trait summary The ranking of beef sires based on the conformation of their female offspring.

Genome (je-nom) All of the genetic information of a living thing. The genome provides a "map" for all the genes, but does not explain the role of each gene, or how the genes work together or affect each other. Mapping the genome is the first step in understanding the genetic makeup of a species.

Genotype (je-no-tip) The genes an animal possesses. These genes may or may not be expressed in their physical appearance (see Table 3-2).

Haploid (hahp-loyd) Cells that contain a single set of chromosomes. Gametes (sex cells) are haploid cells. When gametes are joined, the resulting cell has two sets of chromosomes.

Heritability (hehr-ih-tah-bihl-ih-te) The amount of variation between individuals that is due to genetics.

Heritable trait (hehr-ih-tah-bihl) A trait that can be passed from parent to offspring. Characteristics that are a result of the environment are not heritable, and cannot be passed onto the next generation.

Heterosis (heht-ehr-o-sihs) The increased health, growth, and performance that results from crossing animals with genotypes that are less similar than those found in the population (for example, by crossing animals of two different breeds). Also known as hybrid vigor.

Heterozygous (heht-er-o-zi-guhs) When each allele, or gene, on the chromosome at a specific location is different. For example, an animal exhibiting Bb could pass either of two alleles/genes to its offspring.

Homologous chromosomes (ho-mohl-o-guhs) Chromosomes that are the same size and shape and affect the same traits.

Homozygous (ho-mo-zi-guhs) When both alleles, or genes, on the chromosome at a specific location are the same. For example an animal that exhibits BB can pass only one allele/gene to its offspring.

Inbreeding Mating closely related animals to concentrate a set of genes. The more closely related the animals, the more genes they will have in common. Inbreeding concentrates both desirable and undesirable traits.

Inbreeding depression The decrease in health, growth, and performance that results from regular inbreeding. Inbreeding depression is a major concern in populations with a limited gene pool.

Incomplete dominance A phenotype in which neither gene is completely dominant or completely recessive. The offspring will express a combination of the characteristics of each gene that is different than what either gene would express if it was homozygous.

Inheritance (in-har-i-tens) The passing of genes from one generation to the next.

Karyotype (kar-e-o-tip) A picture of all the chromosomes of an animal (see Figure 3-1). A karyotype is created by stopping mitosis, then staining the chromosomes with a dye. The different band colors in the photograph result because adenine and thymine absorb large amounts of the dye.

Linebreeding A form of inbreeding in which animals with a shared ancestor are mated. That individual may be several generations removed, and may occur in the pedigree numerous times.

Locus (lo-kuhs) The location of a gene on the chromosome. Plural form loci (lo-si).

Meiosis (mi-oh-sihs) The process of cell division that results in four haploid cells, each containing one-half of the genetic material of the parent (see Figure 3-2). Meiosis is the cell division process by which gametes are formed.

Messenger ribonucleic acid (mRNA) The template for the new protein. The mRNA communicates to the ribosome what amino acids are needed to build the specific protein.

Migration (mi-gra-shuhn) The introduction of a new set of genes into a population. This can be achieved on a large scale or small scale by bringing a new male into the breeding program, or by a breed accepting crosses to another breed. For example, when the American Quarter Horse Association determined that Thoroughbreds could be bred into Quarter Horses, and produce registerable offspring, a new set of genes was introduced into the population.

Mitosis (mi-to-sihs) Normal cell division that results in a cell that is identical to the parent cell (see Figure 3-3).Mitosis is the cell division process by which somatic cells in the body divide for body growth or for repair of the body.

Modifier gene A gene that has an effect on how another gene is expressed.

[FIGURE 3-1 OMITTED]

[FIGURE 3-2 OMITTED]

[FIGURE 3-3 OMITTED]

Multiple alleles The existence of more than two alleles for a given gene. Although only two alleles will exist in any given individual, there may be more than two alleles in the population of the species.

Mutagen (myoo-tah-jehn) Something that causes a change in the DNA that is permanent and transmissible to offspring. Mutagens can be chemical, physical, or radioactive in nature.

Mutation (myoo-ta-shuhn) A chemical change in the DNA of a gene, resulting in a new gene or allele. Mutations seldom occur in a population, but can result in rapid changes in the population when they do occur. Mutations can result in either positive or negative traits.

Natural selection Reproductive selection without human interference. Natural conditions determine which animals have the greatest opportunity to reproduce. The concept of "survival of the fittest" is based on natural selection.

Outcrossing Breeding of animals that are less related than the general population. Outcrossing is the opposite of inbreeding and increases the heterozygosity of the offspring.

Ovum(o-vuhm) The female gamete, which carries the DNA from the female parent. Plural is ova (o--vah).

Phenotype (fe-no-tip) The physical expression of genes in an animal. The phenotype is not always an accurate indicator of the genotype. The phenotype does not indicate which genes might be recessive, or which genes may be expressed in an incomplete way.

Plasmid (plahz-mihd) A portion of DNA in a cell that is not part of the chromosomal DNA, and that can reproduce itself.

Polyploid (pohl-e-ployd) An animal that has more than two full sets of chromosomes.

Population genetics The study of frequencies of genes in a population, and how that frequency changes over time. Population genetics focuses on the group of animals, not on the traits of individual specimens.

Qualitative traits Traits that are categorized by their presence or absence (for example, coat color or presence of horns). These traits are usually controlled by a small number of genes.

Quantitative traits Traits that can be measured, such as production of milk or eggs, weight gain, racing speed, and so on. These traits are often controlled by many genes.

Recessive allele (re-sehs-ihv) An allele in a pair that is not expressed in the presence of a dominant allele.

For a recessive allele to be expressed, both alleles in the pair must be recessive. Recessive alleles are labeled with a lowercase letter (for example, b).

Ribonucleic acid (RNA) (ri-bo-nu-kle-ihck ah-sihd) Molecules that are built as a complement to DNA; RNA carries the information to the cell to produce a specific protein.

Ribosome (ri-boh-zohm) The part of the cell that manufactures proteins.

Sex chromosomes Chromosomes that determine the sex of the offspring. In mammals, females are XX and males are XY. Each parent passes on one sex chromosome to the offspring.

Sex-influenced traits Traits that are expressed differently in males and females with the same genotype. Sex-limited traits Both males and females carry the genes for the traits, but the trait is only expressed in one sex. Milk production is an example: Males cannot express the trait; however, males from lines of females that are high producers are more likely to have female offspring that are high producers.

Sex-linked inheritance Genes that are located on parts of the sex chromosomes that are different. Therefore, the gene is only transferred to offspring that inherits the sex chromosome with that gene present.

Somatic cell (so-maht-ihck) Any cell that is not a gamete.

Sperm A male gamete that carries the DNA of the male parent.

Strain A population within a breed of more closely related animals. When animals from different strains are crossed, the population is a strain cross.

Transcription The building of RNA to complement the DNA for a particular protein.

Transfer RNA (tRNA) The RNA molecules that carry the code that determines which amino acids are needed to build a protein, and recruit those proteins from the cytoplasm of the cell for the ribosomes to produce the required protein.

Transgenic (trahnz-gehn-ehk) Genetic material from another source has been introduced into the genetic material of a plant or animal. Transgenic mice with specific traits are often used for human medical research.

Translation The process of using the information from mRNA to assemble amino acids in the correct sequence for a particular protein.

Breeding/Mate Selection

Much thought should go into the decision to create offspring from two animals. The genetics of both animals must be considered to ensure a mating that accomplishes the intended purpose, whether for increasing production of meat or milk, matching a breed standard for a show dog or cat, or producing a fast racehorse. Most species have some diseases that are heritable within the species, or within certain lines in a species. Responsible breeders use caution to ensure that they are not perpetuating undesirable traits in the animals they breed. In some species, such as dogs and cats, overpopulation of animals is a significant issue. When people decide to breed dogs and cats, they should ensure that good homes are available for all of the offspring to ensure they are not contributing to the overpopulation problem. Many terms in animal science specifically relate to the mating and breeding of animals.

Breeding soundness examination A physical examination, usually by a veterinarian, to determine the ability of a male or female to reproduce. A breeding soundness exam of a male should include collection and evaluation of a semen sample. Breeding soundness exams of females should ensure that they are capable of conceiving and carrying a pregnancy to term. Breeding soundness examinations are especially important when purchasing new breeding stock.

Closed herd A herd of animals into which no new animals are introduced.

Congenital disease (cahn-jen-e-tal) A disease or abnormality that has been present since birth, but is not heritable. A congenital disease can occur because of the environment during gestation or birth, and may or may not be due to a genetic change in the animal.

Dam The female parent of an animal.

Estimated Breeding Value (EBV) The value of an animal for breeding estimated by calculating performance of the individual and its relatives compared to the general population.

Expected Progeny Difference (EPD) A calculation that estimates how an individual's offspring will perform compared to other animals of the same generation.

Freemartin (fre-mar-ten) A female calf twin born with a male calf that has a high likelihood of infertility and underdeveloped reproductive organs.

Generation interval The average time between the birth of an animal and its production of offspring. Animals that reach puberty more quickly and have a shorter gestation time have a shorter generation interval than animals that mature more slowly and carry offspring longer.

Get Offspring of a male. Some shows have "Get of Sire" classes, where several offspring from one male are judged as a group.

Heritable disease A disease that is genetically inherited from one or more parent. An animal with a heritable disease has the genes to pass that disease on to its offspring, and use in breeding programs should be very limited. Heritable diseases exist in all species, and are inherited in a variety of ways. It is often desirable to test animals for heritable diseases prior to breeding.

[FIGURE 3-4 OMITTED]

Mate selection The process of identifying the most ideal animal to breed to a particular animal.

Pedigree (ped-e-gre) The written record of an animal's ancestors. In a pedigree, the male ancestors are listed above the female ancestors for each generation (see Figure 3-4).

Produce The cumulative offspring of a female. Some shows have "Produce of Dam" classes, in which several offspring from one female are judged as a group.

Progeny (proh-jehn-e) The cumulative offspring of a sire or dam.

Progeny testing The calculation of how the performance of offspring of a sire or dam compare to their contemporaries.

Sire (sir) The male parent of an animal.

Sire summary Information provided by some breed associations, especially cattle, providing results from national evaluations of sires within a breed.

Animal Breeding

Many specific terms relate to the breeding of animals. Chapter 4 will address the physiology and anatomy of the reproductive process. Chapter 6 will address behaviors associated with breeding and reproduction. This section focuses on terminology related to the reproductive management of animals. Reproduction is a vital aspect of animal science. Successful breeding is necessary to advance a species, and create a more desirable product, whether a meat animal or a companion animal that better serves the owner. The production of milk is not possible without the successful breeding of a female. Although we have made many changes in animals as we have domesticated them, the basics of the breeding process have remained the same. The gestation length for a domestic species is the same as for their analogous wild relatives. The success of breeding depends on having animals that are in good health and managers that are aware of the intricacies of the breeding process.

Terms for Male Animals

Barrow (bar-o) A castrated male pig (see Figure 3-5).

Boar An intact male pig.

Buck An intact male goat or rabbit.

Bull An intact male bovine.

Capon (ka-pohn) A castrated male chicken.

Caponette (ka-pohn-eht) A male chicken that is sterilized with female hormones prior to sexual maturity.

Cockerel (kohck-er-ahl) A young male chicken.

Colt A young male horse.

Dog An intact male canine.

Drake An intact male duck.

Gander (gahn-dehr) An intact male goose.

Gelding (gehl-dihng) A castrated male horse.

Gomer bull (go-mer) A bull that is used to detect estrus in cattle. A gomer bull has been rendered infertile through vasectomization, sterilization, or surgical deviation of the penis to prevent breeding.

In the case of a castrated animal, the animal is treated with testosterone so it will exhibit sexual behavior.

[FIGURE 3-5 OMITTED]

Lapin (lah-pihn) A castrated male rabbit.

Ram An intact male sheep.

Rooster An intact male chicken.

Spotter bull A bull that has been vasectomized and is used to detect estrus in cows. Because he is vasectomized, not castrated, he still produces testosterone but cannot impregnate the cows.

Stallion (stahl-yuhn) An intact male horse.

Steer A castrated male bovine.

Tom An intact male cat or turkey.

Wether A castrated sheep or goat.

[FIGURE 3-5 OMITTED]

Additional Male-Related Terms

Cryptorchid (kriph-tor-kihd) A mammal with one or both of the testicles remaining in the body cavity, and not descending into the scrotum. This condition may require surgical intervention. An animal with both testicles remaining in the body will be infertile, or subfertile, but may still produce male sex hormones and exhibit behaviors similar to those of an intact male.

Ejaculate (e-jahck-yu-la-t) (verb) The release of semen from the reproductive tract of the male. Note the difference in the verb and noun forms of the same spelling.

Ejaculate (e-jahck-yoo-let) (noun) The amount of semen resulting from one ejaculation of the male. Note the difference in the verb and noun forms of the same spelling.

Erection The engorgement of the erectile tissue in the penis with blood, or through straightening of the sigmoid flexure, depending on the species.

Flehmen (fleh-mehn) The upward curling of the lip of a male of a species in response to scents detected from the female.

Semen (se-mehn) The fluid males ejaculate that contains sperm cells and other fluids that nourish and protect the sperm cells, and create volume to facilitate the transport of sperm cells.

Sigmoid flexure (sihg-moyd flehck-sher) A bend in the penis that is extended in some species to achieve an erection

Terms for Female Animals and Offspring

Bitch A female dog.

Broodmare (brood-mar) A female horse whose primary purpose is producing foals.

Calf A young bovine of either gender.

Chick A young chicken of either gender; also used for most companion birds.

[FIGURE 3-6 OMITTED]

Cow A female bovine (see Figure 3-6).

Doe A female goat or rabbit.

Duckling A young duck of either gender.

Ewe (u) A female sheep.

Filly (fihl-e) A young female horse.

Foal (fol) A young horse of either gender.

Gilt A young female pig.

Goose A female goose.

Gosling A young goose of either gender.

Heifer (hehf-er) A young female bovine.

Hen A female chicken, duck, or turkey.

Kid A young goat of either gender.

Kitten A young cat of any gender.

Lamb (lahm) A young sheep of either gender.

Mare A mature female horse.

Piglet A young pig of either gender.

Pullet (puhl-leht) A young female chicken.

Puppy A young dog of either gender.

Queen A female cat.

Sow A mature female pig or guinea pig.

Additional Female-Related Terms

Anestrus (ahn-ehs-truhs) An extended period of sexual inactivity in animals that are seasonally polyestrous or monestrous.

Corpus luteum (kor-puhs loo-te-uhm) The tissue formed after ovulation that eventually will produce progesterone, the hormone that is dominant when the female is pregnant or in diestrus. Corpus luteum is usually abbreviated as CL.

Estrous cycle (ehs-truhs) The pattern of hormonal and behavioral characteristics that mark the reproductive status of females (see Figure 3-7). Each stage of the estrous cycles has unique characteristics. The length of each stage of the cycle and the frequency of cycles vary among species. The following listing is in the order in which the stages of the cycle occur.

* Proestrus (pro-ehs-truhs) A period when follicle-stimulating hormone (FSH) is being released to stimulate follicular growth. The female is not sexually receptive.

* Estrus (ehs-truhs) The period of sexual receptivity. The primary hormone during this period is estrogen. Note that estrus is spelled differently when it refers to one stage of the estrous cycle.

* Metestrus (meht-ehs-truhs) A period following estrus that is characterized by the development of the corpus luteum and production of progesterone.

* Diestrus (di-ehs-truhs) The period during which the animal's body determines pregnancy. During this time, progesterone is the primary hormone. If not pregnant, the animal continues to the proestrus period and back through the complete cycle. If pregnant, the animal continues through gestation.

* Interestrous (ihn-ter-ehs-truhs) A period in cats that occurs if ovulation is not induced via copulation.

* Monestrous (mohn-ehs-truhs) One estrous cycle each year, followed by a period of anestrus.

* Polyestrous (pohl-e-ehs-truhs) Each estrous cycle is immediately followed by another estrous cycle.

* Seasonally polyestrous Each estrous cycle is followed immediately by another estrous cycle during part of the year. Then the female goes into anestrus for a period of time. Seasonally polyestrous animals can either be long-day breeders, in which the lengthening days stimulate a return to reproductive activity, or short-day breeders, in which shortening days stimulate the return to reproductive activity.

[FIGURE 3-7 OMITTED]

Gestation (jehs-ta-shuhn) In mammals, the period of time that the offspring develops in the uterus.

Gravid (grahv-ihd) Pregnant.

Incubation (ihn-kyoo-ba-shuhn) In avians, the length of time fertilized eggs need to be kept in a warm, humid environment to allow development of the young.

Ovulation (oh-vu-la-shuhn) The release of the oocyte (or yolk in the case of birds) from the follicle. In most species, ovulation is spontaneous and occurs regardless of mating; however, some species (rabbits, cats, llamas) are induced ovulators, and must have the stimulation of the penis to induce the production of the hormone necessary for ovulation.

* Ovulation fossa (fah-sah) In horses, ovulation occurs through the center of the ovary. All other species ovulate on the edge of the ovary. The depression that is left when the mare ovulates is the ovulation fossa.

Ovulatory follicle (oh-vu-lah-tor-e) A follicle that has matured and is prepared to ovulate an ovum.

Parturition (pahr-tyoo-rihsh-uhn) The delivery of the offspring and the associated tissues and fluids. Also known as labor.

Primigravida (prih-mih-grahv-ih-dah) First pregnancy.

Primiparous (prih-mih-pahr-uhs) A female that is pregnant for the first time, or has given birth to its first offspring.

Other Breeding-Related Terms

Artificial insemination (AI) AI is the insemination of collected semen into a female by a technician, instead of a male of the species (see Figure 3-8). This is a valuable reproductive management tool. AI allows for the insemination of numerous females with one ejaculate, and allows for preservation and transportation of semen. Precise techniques for collection and insemination vary with species.

Artificial vagina An instrument that imitates the vagina of a female and is used to collect semen from males for analysis or artificial insemination.

Atresia (a-tre-szha) The degeneration of follicles that do not mature to the ovulatory stage. Most follicles go through atresia.

Capacitation (kah-pahs-ih-ta-shuhn) A metabolic change in the sperm cell that gives it the ability to enter and fertilize an egg.

Castration (kahs-tra-shuhn) The removal of the testicles (see Figure 3-9). Castration results in sterility and removes the organs responsible for producing sex hormones in males. This removal is sometimes also called neuter (nu-ter), especially in companion animals.

[FIGURE 3-8 OMITTED]

[FIGURE 3-9 OMITTED]

Colostrum (ko-lah-struhm) The first milk produced for the offspring. Colostrum is rich in antibodies and nutrients and is vital for the young to thrive.

Conception (kohn-sehp-shuhn) The fertilization of the ovum by the sperm resulting in a zygote (zi--go-t).

Conception rate The percentage of animals that get pregnant the first time they are bred in the breeding season. Usually used in relation to cattle.

Dystocia (dihs-tos-e-ah) A difficult birth.

Electro ejaculation (e-lehck-tro-e-jahck-yoo-la-shuhn) Electrical stimulation of nerves in the male reproductive tract to cause ejaculation. This is a useful tool for collecting semen for analysis or for artificial insemination.

Embryo (ehm-bre-o) A developing zygote.

Fertilization (fer-tihl-ih-za-shuhn) The joining of the sperm and the ova.

Fetotomy (fe-toh-to-me) The surgical cutting of the fetus to remove it from the uterus. This is done in the case when the fetus has died, and the female cannot deliver it normally.

Fetus (fe-tuhs) Used to describe an unborn mammal, usually toward the end of gestation. Embryo is used as the descriptor earlier in gestation.

Gamete (gam-et) A mature reproductive cell of either a male or a female.

Gonad (go-nahd) A general term for sex organs. Can refer to either male or female.

Implantation (ihm-plahn-ta-shuhn) The attachment of a fertilized egg to the wall of the uterus. Implantation occurs prior to development of the placenta.

Mastitis (mahs-ti-this) Inflammation of the mammary gland.

Morphology (mor-fah-lo-je) The form and shape of the sperm cells. Sperm cells that are misshapen or malformed (see Figure 3-10) are less likely to be successful in fertilizing an egg.

Motility The ability of a sperm cell to move progressively in a line. When semen is evaluated for quality, the morphology, motility, and concentration (number of sperm cells in a sample) are the primary criteria evaluated.

Oogenesis (o-o-jehn-eh-sihs) The creation of egg cells.

Oophorectomy (o-ohf-o-rehck-to-me) The surgical removal of one or both ovaries. Only the ovaries are removed, leaving the rest of the reproductive tract.

Ovariohysterectomy (o-vahr-e-o-hihs-ter-ehck-to-me) The surgical removal of the ovaries, oviducts, and uterus in females. This procedure results in sterility, and the cessation of reproductive hormone production. Also known as spay (spa), especially in companion animals.

Ovigonium (o-vih-go-ne-uhm) The germ cell from which the oocyte is produced.

[FIGURE 3-10 OMITTED]

Puberty (pu-behr-te) The process through which an immature animal reaches sexual maturity. Age at puberty varies with species, and even in breeds within species. Environment and nutrition have a significant affect on the onset of puberty.

Retained placenta Occurs when the placenta, or parts of the placenta, remain attached to the uterus after parturition. The placenta may cause a significant uterine infection, and result in infertility if the condition is not treated promptly.

Spermatagonium (sper-mah-to-gon-e-uhm) A primary germ cell in the testis of the male that produces the sperm cell.

Spermatogenesis (sper-mah-to-jenn-eh-sihs) The creation of new sperm.

Urethra (yoo-re-thrah) The tubular structure that carries urine out of the body. In males, the urethra also carries sperm from the testicles, through the penis.

Vasectomy (vah-sehk-to-me) The surgical removal of the vas deferens, which is the structure that carries sperm from the testis to the urethra. This results in sterility of the male because the sperm cannot travel from the testes; however, the male still produces sexual hormones and still exhibits male sexual behavior.

Zygote (zi-got) A fertilized egg.

CHAPTER SUMMARY

Breeding and genetics create the foundation for progress in animal species. Careful selection and mating of animals results in the creation of cattle and pigs that produce leaner meat, horses that run faster and jump higher, and dogs that more distinctively represent their breed. To make breeding decisions that move a breeding program in the desired direction, it is important to understand how traits are inherited, and how we can affect what traits are passed on.

Reproduction is a vital part of any animal agriculture effort. Without effective and efficient reproduction, we have no production of meat or milk. In companion animals, control of reproduction is a priority as we fight an ongoing battle with animal overpopulation and the propagation of genetic diseases in animals. A basic understanding of how characteristics are inherited, and the process involved in reproduction is vital for anyone involved in the animal industry.
STUDY QUESTIONS

1. Complete the following table with the correct information:
Species Male Castrate Male Intact

[ILLUSTRATION OMITTED]

Match the stage of the estrous cycle with its description.

2. -- Estrus      a. A period when no activity is occurring.

3. -- Proestrus   b. The period between estrus periods.

4. -- Metestrus   c. The time when FSH is stimulating follicular
                     growth.

5. -- Diestrus    d. The period when the female is receptive to the
                     male.

6. -- Anestrus    e. The time immediately after the cessation of
                     receptive behavior.
7. Which of the following refers to the change in genes due to
   natural selection?

a. Population genetics

b. Genetic drift

c. Genetic waves

d. Gene frequency

8. Which describes the visual appearance of the animal?

a. Phenotype

b. Genotype

c. Heterozygous

d. Homozygous

9. Which breeding strategy results in animals that are the
   most similar genetically?

a. crossbreeding

b. natural selection

c. inbreeding

d. outcrossing

10. A -- gene affects the expression of a color. This gene changes a
   --horse to a palomino.

11. A -- allele is present in the animal, but is not expressed.

12. A male animal with one testicle that does not descend into
   the scrotum is a/an --.

13. The surgical procedure to remove all reproductive organs of a
   female is a/an --.

14. A horse breeder bred a bay stallion and a bay mare, and they
   had a chestnut offspring. In horses, the chestnut color is
   recessive. If bay is represented by B, and chestnut is
   represented by b, what is the genotype of the foal? What is the
   genotype of each parent? What percentage of the offspring of this
   mating would be bay? What percentage would be chestnut?

15. Animal species have a wide range of heritable diseases. Select
   the species of your choice, and conduct an Internet search to
   determine what heritable diseases are of concern in that species.
   Select one disease, research how it is inherited, and make
   a recommendation on how to control the disease in the population.

TABLE 3-1
The number of chromosomes in common animal species

 Number of chromosomes by species

Bovine                        60
Canine                        78
Caprine                       60
Chicken                       78
Equine                        64
Feline                        38
Ovine                         54
Porcine                       38

TABLE 3-2
Color inheritance in horses

            B           b

B           BB          Bb
b           Bb          bb

Using a Punnett square, the percentage of offspring with a certain
genotype can be determined from a mating. In the example above,
each of the parents is phenotypically bay, with a genotype of Bb.
(B is the bay gene, b is the chestnut gene.) Each parent contributes
one color gene to the offspring. Genotypically, 25 percent of foals
will be homozygous bay, 50 percent of the foals will be heterozygous
bay, and 25 percent will be homozygous chestnut.
Phenotypically, 75 percent of the offspring will be bay, and
25 percent will be chestnut.
COPYRIGHT 2008 Delmar Learning
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 2008 Gale, Cengage Learning. All rights reserved.

Article Details
Printer friendly Cite/link Email Feedback
Author:Brady, Colleen
Publication:An Illustrated Guide to Animal Science Terminology
Geographic Code:1USA
Date:Jan 1, 2008
Words:5644
Previous Article:Chapter 2 The animal agriculture industry.
Next Article:Chapter 4 Animal anatomy.
Topics:

Terms of use | Privacy policy | Copyright © 2019 Farlex, Inc. | Feedback | For webmasters