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Animal breeding

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Animal Breeding and Genetics

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Animal breeding

  1. 1. Illustration of DNA Double Helix from Wikipedia. PRINCIPLES OF ANIMAL GENETICS ASM 391 Natural Resources Development College Animal Science Department By E.Msimuko.
  2. 2. Illustration of DNA Double Helix from Wikipedia. Introduction • Genetics is the science of heredity and variation • It is the scientific discipline that deals with the differences and similarities among related individuals • All animals have a predetermined genotype that they inherit from their parents. • However, an animal’s genotype can be manipulated by breeding and more advanced scientific techniques (genetic engineering and cloning).
  3. 3. Illustration of DNA Double Helix from Wikipedia. • For many years, managers of agricultural systems have manipulated the genetic makeup of animals to: • improve productivity, • increase efficiency • and adaptability. • Successful manipulation of the genetic composition of animals requires a depth understanding of fundamental principles of genetics.
  4. 4. Illustration of DNA Double Helix from Wikipedia. Mendelian Genetics • Gregory Mendel is recognized as the father of genetics • in the 1850’s and 1860’s, he developed his theories without any knowledge of cell biology or the science of inheritance- he failed his teachers exams • In later years, genes, chromosomes, and DNA were discovered and people began to understand how and why Mendel’s theories worked. Photo courtesy of Wikipedia.
  5. 5. Illustration of DNA Double Helix from Wikipedia. • Mendel proposed three principles to describe the transfer of genetic material from one generation to the next. • The Principle of Dominance • The Principle of Segregation • The Principle of Independent Assortment The Principle of Dominance – in a heterozygous organism, one allele may conceal the presence of another allele. Aa or Pp
  6. 6. Illustration of DNA Double Helix from Wikipedia. The Principle of Segregation – in a heterozygote, two different alleles segregate from each other during the formation of gametes. Aa individual will produce two gametes- A-alleles and a-alleles The Principle of Independent Assortment – the alleles of different genes segregate, or assort, independently of each other. PpBb x PpBb gives 9:3:3:1 Later studies have shown that there are some important exceptions to Mendel’s Principle of Independent Assortment, but otherwise, these principles are recognized as the basis of inheritance.
  7. 7. Illustration of DNA Double Helix from Wikipedia. Knowledge of which allele has been inherited at one locus gives no information on the allele has been inherited at the other locus P/p B/b PB Pb pB pb 25% 25% 25% 25%
  8. 8. Illustration of DNA Double Helix from Wikipedia. • Mendel’s experiments dealt with the relationship between an organism’s genotype and its phenotype. • Genotype – the genetic composition of an organism. • Phenotype – the observable or measurable characteristics (called traits) of that organism • Two organisms may appear to be similar, but they can have different genotypes. • Similarly, two animals may have the same genotypes, but will appear to be different from each other, if they have been exposed to different environmental conditions throughout their lives.
  9. 9. Illustration of DNA Double Helix from Wikipedia. The relationship between phenotype and genotype is expressed as the following equation: P = G + E P = phenotype – observed attributes (Yield, Quality) G = genotype- A, D, E, and E = environment- breed, Nut. A.H, Climate, housing and research If two individuals with identical genotypes are exposed to the same environmental conditions, such as nutrition, climate, and stress levels, their phenotypes (measurable and observable characteristics) should be the same “What you see is what you get”
  10. 10. Illustration of DNA Double Helix from Wikipedia. • To understand Mendel’s principles and the relationships between phenotype and genotype, it is necessary to understand; • what makes up the genetic material of animals and • how this is transferred from one generation to the next.
  11. 11. Illustration of DNA Double Helix from Wikipedia. Genetic Material The body is made up of millions of cells which have a very complicated structure. These cells are made up of many parts that have specialized roles. 1. Nucleolus 5. Rough Endoplasmic Reticulum 9. Mitochondria 2. Nucleus 6. Golgi Apparatus 10. Vacuole 3. Ribosome 7. Cytoskeleton 11. Cytoplasm 4. Vesicle 8. Smooth Endoplasmic Reticulum 12. Lysosome 13. Centrioles
  12. 12. Illustration of DNA Double Helix from Wikipedia. The nucleus contains chromosomes that are visible under the microscope as dark-staining, rod-like or rounded bodies. Chromosomes occur in pairs in the body cells. The number of chromosomes in each cell is constant for individual species, but it differs among species. Suis-38, caprine-60, carnis 78, galus-78, bovine-60,
  13. 13. Illustration of DNA Double Helix from Wikipedia. Chromosomes are made up of tightly-coiled strands of DNA. DNA is a complex molecule composed of deoxyribose, phosphoric acid, and four bases. Individual genes are located in a fixed position (known as the loci) on the strands of DNA. A chromosome is made up of two chromatids and a centromere. The chromatids are formed from tightly coiled strands of DNA. If these strands of DNA are stretched out, individual genes can be identified.eg DT
  14. 14. Illustration of DNA Double Helix from Wikipedia. A gene is made up of a specific functional sequence of nucleotides, which code for specific proteins. A specific protein is produced when the appropriate apparatus of the cell (the ribosome) reads the code. Image courtesy of Wikipedia.
  15. 15. Illustration of DNA Double Helix from Wikipedia.
  16. 16. Illustration of DNA Double Helix from Wikipedia. • In somatic cells (body cells), chromosomes occur in pairs, known as homologous chromosomes as a result, genes also occur in pairs except in virus(RNA) • Somatic cells are referred to as diploid, or 2n. • Gametes (reproductive cells) are referred to as haploid, or n - do not have paired chromosomes
  17. 17. Illustration of DNA Double Helix from Wikipedia. When discussing different generations in genetics, the first generation is referred to as the parent or P generation. Their offspring are referred to as the first filial or F1 generation. P X P = F1 When individuals from the F1generation are mated with each other, their offspring are referred to as the F2 generation. F1 X F1 =F2
  18. 18. Illustration of DNA Double Helix from Wikipedia. Principle of Dominance • In animals, chromosomes are paired and, therefore, genes are paired. • These paired genes code for the same trait, but they are not identical. • They can have different forms, known as alleles. • For example, sheep and cattle can be polled or horned. • One gene codes for this trait and the two possible forms (alleles) of the gene are polled or horned
  19. 19. Illustration of DNA Double Helix from Wikipedia. Hereford Cattle USDA photo from Wikipedia. Photo from IMS. A capital letter is used to denote the dominant form of the gene (P) and a small letter is used to denote the recessive form of the gene (p). In the example, the polled allele is dominant and is, therefore, denoted by P, while the horned allele is recessive and denoted by p. Because genes are paired, an animal can have three different combinations of the two alleles: PP, Pp, or pp.
  20. 20. Illustration of DNA Double Helix from Wikipedia. • When both genes in a pair take the same form (PP or pp), the animal is referred to as being homozygous for that trait. • An animal with a PP genotype is referred to as homozygous dominant. • An animal with the pp genotype is referred to as homozygous recessive. If one gene in the pair is the dominant allele (P) and the other gene is the recessive allele (p), the animal is referred to as being heterozygous for that trait and its genotype is denoted as Pp. • If an animal has the allele combination PP, it will be polled. • If the combination is pp, the animal will be horned. • If it is a heterozygote, the animal will have both traits (Pp), but the animal will be polled because the polled allele (P) is the dominant form of the gene. Mendel’s principle of dominance states that in a heterozygote, one allele may conceal the presence of another.
  21. 21. Illustration of DNA Double Helix from Wikipedia. In this example, the polled allele is concealing the horned allele and, therefore, is referred to as the dominant allele.
  22. 22. Illustration of DNA Double Helix from Wikipedia. Principle of Segregation • When animals reproduce, they only pass on half of their genetic material to their offspring • The offspring will only receive one allele from each parent. • The Principle of Segregation explains some of the differences that are observed in successive generations of animals and can be used to predict the probability of different combinations of alleles occurring in offspring.
  23. 23. Illustration of DNA Double Helix from Wikipedia. Considering these three types of individuals, six combinations of the various genotypes are possible: • PP x PP (both parents are homozygous polled), • PP x Pp (one homozygous polled parent and one heterozygous polled parent), • PP x pp (one homozygous polled parent and one homozygous horned parent), • Pp x Pp (both parents are heterozygous polled), • Pp x pp (one heterozygous polled parent and one homozygous horned parent), and • pp x pp (both parents are homozygous horned)
  24. 24. Illustration of DNA Double Helix from Wikipedia. The genotypes of the parents can be used to predict the phenotypes of the offspring Predicting the Genotypes and Phenotypes of Offspring by: A punnett square - grid-like method that is used to display and predict the genotypes and phenotypes of offspring from parents with specific alleles. The male genotype is normally indicated at the top and the female genotype is indicated in the vertical margin.
  25. 25. Illustration of DNA Double Helix from Wikipedia. When crossing homozygous dominant parents (PP x PP), all offspring will be homozygous dominant polled individuals. All polled
  26. 26. Illustration of DNA Double Helix from Wikipedia. When crossing homozygous recessive parents (pp x pp), all of the offspring will be horned (homozygous recessive) individuals.
  27. 27. Illustration of DNA Double Helix from Wikipedia. When crossing a heterozygous parent with a homozygous dominant parent (Pp x PP), the expected offspring would occur in a 1:1 ratio of homozygous dominant to heterozygous individuals. Phenotypically, all offspring would be polled. When crossing a homozygous dominant parent with a homozygous recessive parent (PP x pp), all offspring would be heterozygous and polled.
  28. 28. Illustration of DNA Double Helix from Wikipedia. • If two heterozygous parents are crossed (Pp x Pp), one can expect a genotypic ratio of 1:2:1, with one homozygous dominant polled, two heterozygous polled, and one homozygous recessive horned individuals. • The expected phenotypic ratio of offspring would be 3:1 (polled to horned).
  29. 29. Illustration of DNA Double Helix from Wikipedia. . Segregation Alleles separate during meiosis
  30. 30. Illustration of DNA Double Helix from Wikipedia. Considering Multiple Traits-Dihybrid Cross Commonly, there are multiple traits that need to be considered when mating animals. For example, consider that cattle can be horned or polled and white-faced or red-faced. The horns and red-faced coloring are recessive traits. If two individuals with two pairs of heterozygous genes (each affecting a different trait) are mated, the expected genotypic and phenotypic ratios would be:
  31. 31. Illustration of DNA Double Helix from Wikipedia.
  32. 32. Illustration of DNA Double Helix from Wikipedia. Genotypes – 1 PPWW, 2 PPWw, 2 PpWW, 4 PpWw, 1 PPww, 2 Ppww, 1 ppWW, 2 ppWw, and 1 ppww; Phenotypes – 9 polled, white-faced; 3 polled, red-faced; 3 horned, white- faced; and 1 horned, red-faced offspring.
  33. 33. Illustration of DNA Double Helix from Wikipedia. The Law of Independent Assortment • When considering multiple traits, Mendel hypothesized that genes for different traits are separated and distributed to gametes independently of one another. • Therefore, when considering polled and white-faced traits, Mendel assumed that there was no relationship between how they were distributed to the next generation. In most cases, genes do assort independently. • However, advances in genetics have shown that an abnormal situation, called crossing-over, can occur between genes for different traits. • Crossing-over is an exchange of genes by homologous chromosomes during the synapses of meiosis prior to the formation of the sex cells or gametes.
  34. 34. Illustration of DNA Double Helix from Wikipedia. 10. Independent Assortment Bb diploid (2n) B b meiosis I B B b b sperm haploid (n) meiosis II • Chromosomes separate independently of eachother Bb Ff b F B f b f B F Bb Ff Bb Ff This means all gametes will be different!
  35. 35. Illustration of DNA Double Helix from Wikipedia. Other Concepts in Genetics • Non-traditional inheritance involves alleles that are not dominant or recessive. • Incomplete, or partial dominance, & co-dominance are two examples of non-traditional inheritance. • Recent studies in sheep has indicated another form of inheritance called POLAR DOMINANCE • Partial, or incomplete, dominance occurs when the heterozygous organism exhibits a trait in-between the dominant trait and the recessive trait. eg Homozygous mice are black (BB) or white (bb) and the heterozygous mice will be grey (Bb). When a pure, brown-eyed sheep is crossed with a pure, green-eyed sheep, blue-eyed offspring are produced.
  36. 36. Illustration of DNA Double Helix from Wikipedia. Codominance • Codominance occurs when a heterozygote offspring exhibits traits found in both associated homozygous individuals. • An example of codominance is the feather color of chickens. • If a homozygous black rooster is mated to a homozygous white hen, the heterozygous offspring would have both black feathers and white feathers • Roan is a coat color in horses (sometimes dogs and cattle) that is a mixture of base coat colored hairs (ex. black, chestnut) and white hairs. Neither the base coat color or the white hairs are dominant nor do they blend to create an intermediate color.
  37. 37. Illustration of DNA Double Helix from Wikipedia. The roan animal actually has both colored and white hairs. Photo courtesy of Wikipedia. • Under these circumstances, neither allele is dominant and neither is recessive. • Therefore, each allele is denoted by a capital letter.
  38. 38. Illustration of DNA Double Helix from Wikipedia. EPISTASIS It is possible for more than one gene to control a single trait This type of interaction between two nonallelic genes is referred to as epistasis. When two or more genes influence a trait, an allele of one of them may have an epistatic, or overriding, effect on the phenotype. Comb shape in chickens is an example of an epistatic relationship.
  39. 39. Illustration of DNA Double Helix from Wikipedia. Mutations and Other Chromosomal Abnormalities Genes have the capability of duplicating themselves, but sometimes a mistake is made in the duplication process resulting in a mutation. The new gene created by this mutation will cause a change in the code sent by the gene to the protein formation process. Some mutations cause defects in animals, while others may be beneficial. Mutations are responsible for variations in coat color, size, shape, behavior, and other traits in several species of animals. The beneficial mutations are helpful to breeders trying to improve domestic animals.
  40. 40. Illustration of DNA Double Helix from Wikipedia. Changes in chromosomes are reflected in the phenotypes of animals. Some chromosomal changes will result in abnormalities, while others are lethal and result in the death of an animal shortly after fertilization, during prenatal development, or even after birth. Changes that can occur in chromosomes during meiosis include: • Changes in the chromosome number, • Translocation or deletion – chromosome breakage, and • Inversion and insertion – the rearrangement of genes on a chromosome.
  41. 41. Illustration of DNA Double Helix from Wikipedia. Sex-Linked Traits • Sex-linked traits involve genes that are carried only on the X or Y chromosomes, which are involved in determining the sex of animals. • The female genotype is XX, while the male genotype is XY. • The X chromosome is larger and longer than the Y chromosome, which means a portion of the X chromosome does not pair with genes on the Y chromosome • Additionally, a certain portion of the Y chromosome does not link with the X chromosome. • The traits on this portion of the Y chromosome are transmitted only from fathers to sons. • Sex-linked traits are often recessive and are covered up in the female mammal by dominant genes.
  42. 42. Illustration of DNA Double Helix from Wikipedia. • The expression of certain genes, which are carried on the regular body chromosomes of animals, is also affected by the sex of the animal. • The sex of an animal may determine whether a gene is dominant or recessive (Ex. Scurs in polled European cattle). • In poultry, the male has the genotype XX, while the female has the genotype Xw. • An example of a sex-linked trait in poultry is the barring of Barred Plymouth Rock chickens. If barred hens are mated to non-barred males, all of the barred chicks from this cross are males, and the non-barred chicks are females.
  43. 43. Illustration of DNA Double Helix from Wikipedia. Sex limited traits
  44. 44. Illustration of DNA Double Helix from Wikipedia. GENETIC OF ANIMAL BREEDING GENETIC SELECTION What is the “BEST” Animal? • Permanent improvements in domestic animals can be made by genetic selection through natural or artificial means. • Natural selection occurs in wild animals, while artificial selection is planned and controlled by humans.
  45. 45. Illustration of DNA Double Helix from Wikipedia. Animals that exhibit desirable traits are selected and mated. Animals that exhibit undesirable traits are not allowed to reproduce or are culled from the herd. Trait- measurable attributes of an individual presence of horns; Calving easy; Growth; litter size Phenotype- measurable category/level for a trait in an individua Horned, polled, assisted, not assisted; WWT, 5,8,1
  46. 46. Illustration of DNA Double Helix from Wikipedia. • The goal of selection is to increase the number of animals with optimal levels of performance, while culling individuals with poorer performance. • Genetic improvement is a slow process • Artificial insemination and embryo transfer are breeding methods that are commonly used to decrease the time taken to improve a trait. • Animals with a best set of genes may have the best Breeding value
  47. 47. Illustration of DNA Double Helix from Wikipedia. • Traits are passed from parents to offspring, but some traits are more heritable than other traits • Heritability is a measure of the strength of the relationship between BV and phenotype values for a trait in a population • That is, the genotype of an individual will be expressed more strongly and environment will be less influential for particular traits
  48. 48. Illustration of DNA Double Helix from Wikipedia. Trait Sheep Swine Cattle Weaning weight 15-25% 15-20% 15-27% Post-weaning gain efficiency 20-30% 20-30% 40-50% Post-weaning rate of gain 50-60% 25-30% 50-55% Feed efficiency 50% 12% 44% Fertility 1.0% Heritability of Various Traits in Livestock High h2 Phenotypes are good indicators Low h2 Phenotypes reveals little about BVs
  49. 49. Illustration of DNA Double Helix from Wikipedia. Quantitative and Qualitative Traits Quantitative traits • Controlled large number of genes, • Economical traits • Exhibit normal distribution and phenotypes show continuous express- additive gene effect • Affect genes with large effect Qualitative Traits • Controlled by dominant or recessive genes, • Non additive gene and non- continuous • Single gene
  50. 50. Illustration of DNA Double Helix from Wikipedia. Quantitative genetics
  51. 51. Illustration of DNA Double Helix from Wikipedia. Measuring Heritable Variation • The value of quantitative traits such a mohair length or size or in dogs-running speed is determined by their genes operating within their environment. • The size of how a spp grows is affected not only by the genes inherited from their parents, but the conditions under which they grow up.
  52. 52. Illustration of DNA Double Helix from Wikipedia. Measuring Heritable Variation • For a given individual the value of its phenotype (P) (e.g. the weight of a broiler in grams) can be considered to consist of two parts -- the part due to genotype (G) and the part due to environment (E) • P = G + E. • G is the expected value of P for individuals with that genotype. Any difference between P and G is attributed to environmental effects.
  53. 53. Illustration of DNA Double Helix from Wikipedia. Measuring Heritable Variation • The quantitative genetics approach depends on taking a population view and tracking variation in phenotype and whether this variation has a genetic basis. • We measure variation in a sample using a statistical measure called the variance. The variance measures how different individuals are from the mean and the spread of the data. • FYI: Variance is the average squared deviation from the mean. Standard deviation is the square root of the variance.
  54. 54. Illustration of DNA Double Helix from Wikipedia. CHARACTERIZING A NORMAL DISTRIBUTION Mean and variance are two quantities that describe a normal distribution. MEAN VARIANCE
  55. 55. Illustration of DNA Double Helix from Wikipedia. USEFUL PARAMETERS FOR QUANTITATIVE GENETICS  Mean: The sum of all measurements divided by the number of measurements    i n x NN xxx x 1...21  Variance: The average squared deviation of the observations from the mean        2 22 2 2 1 1     xx NN xxxxxx Variance i n
  56. 56. Illustration of DNA Double Helix from Wikipedia. CORRELATIONS AMONG CHARACTERS OR RELATIVES 0 + — Covariance:     yyxx N yxCov ji   1 ,
  57. 57. Illustration of DNA Double Helix from Wikipedia. What is heritability?
  58. 58. Illustration of DNA Double Helix from Wikipedia. What is heritability? • heritability is the proportion of the total phenotypic variation controlled by genetic rather than environmental factors.
  59. 59. Illustration of DNA Double Helix from Wikipedia. What is heritability? • heritability is the proportion of the total phenotypic variation controlled by genetic rather than environmental factors.
  60. 60. Illustration of DNA Double Helix from Wikipedia. The total phenotypic variance may be decomposed: VP = total phenotypic variance
  61. 61. Illustration of DNA Double Helix from Wikipedia. The total phenotypic variance may be decomposed: VP = total phenotypic variance VG = total genetic variance
  62. 62. Illustration of DNA Double Helix from Wikipedia. The total phenotypic variance may be decomposed: VP = total phenotypic variance VG = total genetic variance VE = environmental variance
  63. 63. Illustration of DNA Double Helix from Wikipedia. The total phenotypic variance may be decomposed: VP = total phenotypic variance VG = total genetic variance VE = environmental variance VP = VG + VE
  64. 64. Illustration of DNA Double Helix from Wikipedia. The total phenotypic variance may be decomposed: VP = total phenotypic variance VG = total genetic variance VE = environmental variance heritability = VG/VP (broad-sense)
  65. 65. Illustration of DNA Double Helix from Wikipedia. The total genetic variance (VG) may be decomposed:
  66. 66. Illustration of DNA Double Helix from Wikipedia. The total genetic variance (VG) may be decomposed: VA = additive genetic variance
  67. 67. Illustration of DNA Double Helix from Wikipedia. The total genetic variance (VG) may be decomposed: VA = additive genetic variance VD = dominance genetic variance
  68. 68. Illustration of DNA Double Helix from Wikipedia. The total genetic variance (VG) may be decomposed: VA = additive genetic variance VD = dominance genetic variance VI = epistatic (interactive) genetic variance
  69. 69. Illustration of DNA Double Helix from Wikipedia. The total genetic variance (VG) may be decomposed: VA = additive genetic variance VD = dominance genetic variance VI = epistatic (interactive) genetic variance VG = VA + VD + VI
  70. 70. Illustration of DNA Double Helix from Wikipedia. The total genetic variance (VG) may be decomposed: VA = additive genetic variance VD = dominance genetic variance VI = epistatic (interactive) genetic variance heritability = h2 = VA/VP (narrow sense)
  71. 71. Illustration of DNA Double Helix from Wikipedia. Estimating heritability
  72. 72. Illustration of DNA Double Helix from Wikipedia. HERITABILITY  The heritability (h2) of a trait is a measure of the degree of resemblance between relatives. h2 = additive genetic variance (VA)/ phenotypic variance (VP) Heritability ranges from 0 to 1 (Traits with no genetic variation have a heritability of 0)
  73. 73. Illustration of DNA Double Helix from Wikipedia. HERITABILITY h2 = VA / VP = VA / (VG + VE)  Since heritability is a function of the environment (VE), it is a context dependent measure. It is influenced by both,  The environment that organisms are raised in, and  The environment that they are measured in.
  74. 74. Illustration of DNA Double Helix from Wikipedia. ESTIMATING HERITABILITY FROM REGRESSION slope = b = Cov (x,y)/Var (x) Method of estimation COV(x,y) h2 Slope (b) Offspring-Single parent ½ VA 2b b = ½ h2 Half-sib ¼ VA 4b b = ¼ h2 Offspring-Grandparent ¼ VA 4b b = ¼ h2 Offspring-Midparent - b b = h2
  75. 75. Illustration of DNA Double Helix from Wikipedia. HERITABILITY OF BEAK DEPTH IN DARWINS’ FINCHES
  76. 76. Illustration of DNA Double Helix from Wikipedia. IN: Falconer & Mackay. Introduction to Quantitative Genetics.1996. Longman. HERITABILITIES FOR SOME TRAITS IN ANIMAL SPECIES h2 (%)
  77. 77. Illustration of DNA Double Helix from Wikipedia. Estimating heritability • one common approach is to compare phenotypic scores of parents and their offspring:
  78. 78. Illustration of DNA Double Helix from Wikipedia. Estimating heritability • one common approach is to compare phenotypic scores of parents and their offspring: Junco tarsus length (cm) Cross Midparent value Offspring value
  79. 79. Illustration of DNA Double Helix from Wikipedia. Estimating heritability • one common approach is to compare phenotypic scores of parents and their offspring: Junco tarsus length (cm) Cross Midparent value Offspring value F1 x M1 4.34 4.73
  80. 80. Illustration of DNA Double Helix from Wikipedia. Estimating heritability • one common approach is to compare phenotypic scores of parents and their offspring: Junco tarsus length (cm) Cross Midparent value Offspring value F1 x M1 4.34 4.73 F2 x M2 5.56 5.31
  81. 81. Illustration of DNA Double Helix from Wikipedia. Estimating heritability • one common approach is to compare phenotypic scores of parents and their offspring: Junco tarsus length (cm) Cross Midparent value Offspring value F1 x M1 4.34 4.73 F2 x M2 5.56 5.31 F3 x M3 3.88 4.02
  82. 82. Illustration of DNA Double Helix from Wikipedia.  Slope = h2 Regress offspring value on midparent value
  83. 83. Illustration of DNA Double Helix from Wikipedia. Heritability estimates from other regression analyses Comparison Slope
  84. 84. Illustration of DNA Double Helix from Wikipedia. Heritability estimates from other regression analyses Comparison Slope Midparent-offspring h2
  85. 85. Illustration of DNA Double Helix from Wikipedia. Heritability estimates from other regression analyses Comparison Slope Midparent-offspring h2 Parent-offspring 1/2h2
  86. 86. Illustration of DNA Double Helix from Wikipedia. Heritability estimates from other regression analyses Comparison Slope Midparent-offspring h2 Parent-offspring 1/2h2 Half-sibs 1/4h2
  87. 87. Illustration of DNA Double Helix from Wikipedia. Heritability estimates from other regression analyses Comparison Slope Midparent-offspring h2 Parent-offspring 1/2h2 Half-sibs 1/4h2 First cousins 1/8h2
  88. 88. Illustration of DNA Double Helix from Wikipedia. Heritability estimates from other regression analyses Comparison Slope Midparent-offspring h2 Parent-offspring 1/2h2 Half-sibs 1/4h2 First cousins 1/8h2 • as the groups become less related, the precision of the h2 estimate is reduced.
  89. 89. Illustration of DNA Double Helix from Wikipedia. Role of reproduction in genetic improvement DGy = SD * h2 GI where DGy= rate of genetic progress per year (diff. bwn.av.peformance of superior parents selected to parent the next generation and the herd Role of reproduction in genetic improvement
  90. 90. Illustration of DNA Double Helix from Wikipedia. SOW 1ST LITER 2ND LITER 1(4) 6 4 0 -2 0 0 2 (2) 4 3 -2 -3 4 6 3 (6) 8 12 2 6 4 12 4 (5) 7 8 1 2 1 2 5 (3) 5 3 -1 -3 1 3 Σ 30 30 0 0 10 23 Mean (4) 6 6 h2 = 2* 23/10 = 4.6
  91. 91. Illustration of DNA Double Helix from Wikipedia. Heritabilities vary between 0 and 1
  92. 92. Illustration of DNA Double Helix from Wikipedia. Cross-fostering is a common approach Heritability of beak size in song sparrows
  93. 93. Illustration of DNA Double Helix from Wikipedia. Q: Why is knowing heritability important?
  94. 94. Illustration of DNA Double Helix from Wikipedia. Q: Why is knowing heritability important? A: Because it allows us to predict a trait’s response to selection
  95. 95. Illustration of DNA Double Helix from Wikipedia. Q: Why is knowing heritability important? A: Because it allows us to predict a trait’s response to selection Let S = selection differential
  96. 96. Illustration of DNA Double Helix from Wikipedia. Q: Why is knowing heritability important? A: Because it allows us to predict a trait’s response to selection Let S = selection differential Let h2 = heritability
  97. 97. Illustration of DNA Double Helix from Wikipedia. Q: Why is knowing heritability important? A: Because it allows us to predict a trait’s response to selection Let S = selection differential Let h2 = heritability Let R = response to selection
  98. 98. Illustration of DNA Double Helix from Wikipedia. Q: Why is knowing heritability important? A: Because it allows us to predict a trait’s response to selection Let S = selection differential Let h2 = heritability Let R = response to selection R = h2S
  99. 99. Illustration of DNA Double Helix from Wikipedia. THE UNIVARIATE BREEDERS’ EQUATION: R = h2 S Response to Selection Selection differential Heritability Where: P A2 V V h  (Additive Genetic Variance) (Phenotypic Variance)
  100. 100. Illustration of DNA Double Helix from Wikipedia. This is why it’s called “regression”: offspring “regress” toward the mean! S is the Selection Differential
  101. 101. Illustration of DNA Double Helix from Wikipedia. S RESPONSE TO SELECTION WHEN h2 = 1/3  The selection differential (S) = mean of selected individuals – mean of the base population  The response to selection: R = h2S S
  102. 102. Illustration of DNA Double Helix from Wikipedia.
  103. 103. Illustration of DNA Double Helix from Wikipedia. VISUALIZING THE SELECTION DIFFERENTIAL
  104. 104. Illustration of DNA Double Helix from Wikipedia. RESPONSE TO SELECTION  For a given intensity of selection, the response to selection is determined by the heritability. High heritability Low heritability
  105. 105. Illustration of DNA Double Helix from Wikipedia. R = h2 S ESTIMATING h2 USING THE BREEDER’S EQUATION    PP OO S R hSlope    * * 2
  106. 106. Illustration of DNA Double Helix from Wikipedia. Predicting the response to selection Example: the large ground finch, Geospiza magnirostris
  107. 107. Illustration of DNA Double Helix from Wikipedia. Predicting the response to selection Example: the large ground finch, Geospiza magnirostris Mean beak depth of survivors = 10.11 mm
  108. 108. Illustration of DNA Double Helix from Wikipedia. Predicting the response to selection Example: the large ground finch, Geospiza magnirostris Mean beak depth of survivors = 10.11 mm Mean beak depth of initial pop = 8.82 mm
  109. 109. Illustration of DNA Double Helix from Wikipedia. Predicting the response to selection Example: the large ground finch, Geospiza magnirostris Mean beak depth of survivors = 10.11 mm Mean beak depth of initial pop = 8.82 mm S = 10.11 – 8.82 = 1.29
  110. 110. Illustration of DNA Double Helix from Wikipedia. Predicting the response to selection Example: the large ground finch, Geospiza magnirostris Mean beak depth of survivors = 10.11 mm Mean beak depth of initial pop = 8.82 mm S = 10.11 – 8.82 = 1.29 h2 = 0.72
  111. 111. Illustration of DNA Double Helix from Wikipedia. Predicting the response to selection Example: the large ground finch, Geospiza magnirostris Mean beak depth of survivors = 10.11 mm Mean beak depth of initial pop = 8.82 mm S = 10.11 – 8.82 = 1.29 h2 = 0.72 R = h2S = (1.29)(0.72) = 0.93
  112. 112. Illustration of DNA Double Helix from Wikipedia. Predicting the response to selection Example: the large ground finch, Geospiza magnirostris Mean beak depth of survivors = 10.11 mm Mean beak depth of initial pop = 8.82 mm S = 10.11 – 8.82 = 1.29 h2 = 0.72 R = h2S = (1.29)(0.72) = 0.93 Beak depth next generation = 10.11 + 0.93 = 11.04 mm
  113. 113. Illustration of DNA Double Helix from Wikipedia. RESEMBLANCE BETWEEN RELATIVES  When there is genetic variation for a character there will be a resemblance between relatives.  Relatives will have more similar trait values to each other than to unrelated individuals.
  114. 114. Illustration of DNA Double Helix from Wikipedia. offspring offspring parents offspring h2 ≈ 0 h2 ≈ ½ h2 ≈ 1 h2 is the regression (slope) of offspring on parents parents parents Definition of the regression coefficient (slope): byx = cov(x,y)/var(x)
  115. 115. Illustration of DNA Double Helix from Wikipedia. • Here x is the midparent value (parental mean), y is the offspring • The higher the slope, the better offspring resemble their parents. • In other words, the higher the heritability, the better offspring trait values are predicted by parental trait values.
  116. 116. Illustration of DNA Double Helix from Wikipedia. Evolutionary response to selection • We want to be able to measure the effect of selection on a population. • This is called the Response to Selection and is defined as the difference between the mean trait value for the offspring generation and the mean trait value for the parental generation i.e. the change in trait value from one generation to the next.
  117. 117. Illustration of DNA Double Helix from Wikipedia. ARTIFICIAL SELECTION IN DOMESTIC ANIMALS  Grey Jungle fowl
  118. 118. Illustration of DNA Double Helix from Wikipedia.
  119. 119. Illustration of DNA Double Helix from Wikipedia.
  120. 120. Illustration of DNA Double Helix from Wikipedia. RESEMBLANCE BETWEEN RELATIVES DEPENDS ON THE DEGREE OF RELATIONSHIP Monozygotic twins Full sibs Parent-offspring Half sibs Slope of a plot of two variables (x,y) = Cov (x,y) / Var (x) x y
  121. 121. Illustration of DNA Double Helix from Wikipedia. DEGREE OF RELATEDNESS AND THE COMPONENTS OF PHENOTYPIC COVARIANCE VA = additive genetic variance VD = dominance genetic variance VEs = variance due to shared environment Relationship Phenotypic covariance Monozygotic twins: VA + VD + VEs Parent-offspring ½ VA Full sibs (½ VA) +(¼ VD) +VEs Half sibs, or Grandparent – grandchild ¼ VA
  122. 122. Illustration of DNA Double Helix from Wikipedia. Modes of selection on quantitative traits
  123. 123. Illustration of DNA Double Helix from Wikipedia. Modes of selection on quantitative traits
  124. 124. Illustration of DNA Double Helix from Wikipedia. Modes of selection on quantitative traits
  125. 125. Illustration of DNA Double Helix from Wikipedia. Response to Directional Selection:
  126. 126. Illustration of DNA Double Helix from Wikipedia. Response to Directional Selection:
  127. 127. Illustration of DNA Double Helix from Wikipedia. FACTORS AFFECTING GENETIC CHANGE AND PROGRESS • Selection intensity- measures how choosy breeders are deciding which animal to selected • Selection differential- variability of BVs within a population for a trait under selection • Generation interval- total time required to replace one generation with the nesxt • Accuracy of selection- measure of strength of relationship between BV and their predictions for a trait under question.
  128. 128. Illustration of DNA Double Helix from Wikipedia. • Breeding systems aim to improve a single trait or multiple traits. • Single trait selection – aimed at improving one trait in a breeding program with little or no regard for improvement in other (associated) traits. Determine some economic value of a trait. • Multiple trait selection – aims to simultaneously improve a number of traits. • Theoretically, multiple trait selection should result in a faster rate of gain toward a specific objective.
  129. 129. Illustration of DNA Double Helix from Wikipedia. • Most domestic species now have a recognized system in place that allows breeders to estimate the genetic merit of individuals. • In the most cattle, sheep, goat, and swine breeders use expected progeny differences (EPDs). • EPDs are used to compare animals from the same species and breed. • For EPD values to be used effectively, one needs to know the breed averages, the accuracy of the EPDs, and who estimated the EPDs. • A high EPD is not necessarily good; it depends on the trait being considered and breeding objectives.
  130. 130. Illustration of DNA Double Helix from Wikipedia. Dolly the Sheep (the first mammal cloned from adult cells) and many other species have been cloned this way. Worldwide, the institute that has cloned the most species is Texas A&M University, College of Veterinary Medicine, which to date has cloned cattle, swine, a goat, a horse, deer, and a cat.
  131. 131. Illustration of DNA Double Helix from Wikipedia.
  132. 132. Illustration of DNA Double Helix from Wikipedia. The possibility for selecting desired traits at the cellular level holds exciting implications for the genetic improvement of domestic animals.
  133. 133. Illustration of DNA Double Helix from Wikipedia. Summary • Post-genomic genetics has enormous promise for tracking down the genes involved in common complex diseases • Currently our ability to exploit this potential is limited by – study size – difficulty of correcting for confounding factors
  134. 134. Illustration of DNA Double Helix from Wikipedia. Methods of Selection • Individual and family • Half sibs- usually sire families which are the offspring of same bull but with different mothers • Full-sibs- animals sharing both parents eg piglets • Individual selection- on the basis of their own performance (mass selection)
  135. 135. Illustration of DNA Double Helix from Wikipedia. • Simplest method Also called performance testing Takes into account of all individual additive genetic variation that exist in the population • Family selection- based on the average value for the family and makes no separate of individuals • Advantages: i. Traits with low heritability ii. Accounts for environmental variation iii. Good when the family size is large However, it tend to increase the rate of inbreeding
  136. 136. Illustration of DNA Double Helix from Wikipedia. • Within family selection-choosing the best individuals from each family • Progeny testing: • Parents/ pedigree • Computer/ breedplan
  137. 137. Illustration of DNA Double Helix from Wikipedia. Several genes influence some traits. For example, rate of growth is a trait that is influenced by appetite, energy expenditure, feed efficiency, and body composition. Photo by Brian Prechtel courtesy of USDA Agricultural Research Service.
  138. 138. Illustration of DNA Double Helix from Wikipedia. • Reproduction plays a major role in the genetic improvement of farm animals through the application of artificial insemination (AI) and multiple ovulation & embryo transfer (MOET). These help to increase selection differentials on the male and female sides respectively, leading to significant increase in the rate of genetic progress per year, as apparent from the equation below: Role of reproduction in genetic improvement
  139. 139. Illustration of DNA Double Helix from Wikipedia. DGy = SD * h2 GI where DGy= rate of genetic progress per year (diff. bwn.av.peformance of superior parents selected to parent the next generation and the herd average) SD = selection differential h2 = heritability estimate, and GI = generation interval in years. Role of reproduction in genetic improvement
  140. 140. Illustration of DNA Double Helix from Wikipedia. Role of reproduction in genetic improvement
  141. 141. Illustration of DNA Double Helix from Wikipedia. SOW 1ST LITER 2ND LITER 1(4) 6 4 0 -2 0 0 2 (2) 4 3 -2 -3 4 6 3 (6) 8 12 2 6 4 12 4 (5) 7 8 1 2 1 2 5 (3) 5 3 -1 -3 1 3 Σ 30 30 0 0 10 23 Mean (4) 6 6 h2 = 2* 23/10 = 4.6
  142. 142. Illustration of DNA Double Helix from Wikipedia. FACTORS AFFECTING GENETIC CHANGE AND PROGRESS • Selection intensity- measures how choosy breeders are deciding which animal to selected • Selection differential- variability of BVs within a population for a trait under selection • Generation interval- total time required to replace one generation with the nesxt • Accuracy of selection- measure of strength of relationship between BV and their predictions for a trait under question.
  143. 143. Illustration of DNA Double Helix from Wikipedia. • Breeding systems aim to improve a single trait or multiple traits. • Single trait selection – aimed at improving one trait in a breeding program with little or no regard for improvement in other (associated) traits. Determine some economic value of a trait. • Multiple trait selection – aims to simultaneously improve a number of traits. • Theoretically, multiple trait selection should result in a faster rate of gain toward a specific objective.
  144. 144. Illustration of DNA Double Helix from Wikipedia. • Most domestic species now have a recognized system in place that allows breeders to estimate the genetic merit of individuals. • In the most cattle, sheep, goat, and swine breeders use expected progeny differences (EPDs). • EPDs are used to compare animals from the same species and breed. • For EPD values to be used effectively, one needs to know the breed averages, the accuracy of the EPDs, and who estimated the EPDs. • A high EPD is not necessarily good; it depends on the trait being considered and breeding objectives.
  145. 145. Illustration of DNA Double Helix from Wikipedia. FACTORS THAT AFFECT GENETIC PROPERTIES OF A POPULATION • Hardy-Weinberg Law: • Population size • Fertility and viability • Mutation • Immigration/migration • Mating system • selection
  146. 146. Illustration of DNA Double Helix from Wikipedia. Modern Genetics • In recent years, traditional methods of improvement through selection and breeding have been superseded by genetic manipulation. • A substantial amount of research has focused on direct manipulation of genes and DNA. • transferring a gene from one individual to another • This area of genetic manipulation makes important contributions to domesticated animals in relation to immunology, vaccines, aging, and cancer.eg bioengineered to have a gene for mastitis resistance
  147. 147. Illustration of DNA Double Helix from Wikipedia. The implications for introducing superior production, conformation, and disease- resistant traits into domestic animals through gene transfer hold considerable promise in the genetic improvement of animals. Cloning Embryonic cloning of animals involves the chemical or surgical splitting of developing embryos shortly after fertilization and, consequently, developing two identical individuals. It has been performed successfully in several species of animals
  148. 148. Illustration of DNA Double Helix from Wikipedia. Dolly the Sheep (the first mammal cloned from adult cells) and many other species have been cloned this way. Worldwide, the institute that has cloned the most species is Texas A&M University, College of Veterinary Medicine, which to date has cloned cattle, swine, a goat, a horse, deer, and a cat.
  149. 149. Illustration of DNA Double Helix from Wikipedia.
  150. 150. Illustration of DNA Double Helix from Wikipedia. The possibility for selecting desired traits at the cellular level holds exciting implications for the genetic improvement of domestic animals.
  151. 151. Illustration of DNA Double Helix from Wikipedia. Summary • Post-genomic genetics has enormous promise for tracking down the genes involved in common complex diseases • Currently our ability to exploit this potential is limited by – study size – difficulty of correcting for confounding factors
  152. 152. Illustration of DNA Double Helix from Wikipedia. Methods of Selection • Individual and family • Half sibs- usually sire families which are the offspring of same bull but with different mothers • Full-sibs- animals sharing both parents eg piglets • Individual selection- on the basis of their own performance (mass selection)
  153. 153. Illustration of DNA Double Helix from Wikipedia. • Simplest method Also called performance testing Takes into account of all individual additive genetic variation that exist in the population • Family selection- based on the average value for the family and makes no separate of individuals • Advantages: i. Traits with low heritability ii. Accounts for environmental variation iii. Good when the family size is large However, it tend to increase the rate of inbreeding
  154. 154. Illustration of DNA Double Helix from Wikipedia. • Within family selection-choosing the best individuals from each family • Progeny testing: • Parents/ pedigree • Computer/ breedplan
  155. 155. Illustration of DNA Double Helix from Wikipedia. Animal Breeding Systems UNIT 4
  156. 156. Illustration of DNA Double Helix from Wikipedia. • Name and explain common breeding systems used in livestock production • Explain the effects, advantages and disadvantages of using various breeding systems • Indentify the factors involved in selecting a breeding system • Calculate the percentage of parental stock in offspring using various breeding systems Objectives
  157. 157. Illustration of DNA Double Helix from Wikipedia. • Breed for environment- to increase performance • Increase animal yield • Improve animal products • Develop methods of disease control • Extend range of animal products • Conservation of genetic resources • Develop new animals • Scientific • Ornaments, sports, and show purpose Roles of animal breeding
  158. 158. Illustration of DNA Double Helix from Wikipedia. • 2 basic Breeding systems – Straight breeding • Mating animals of the same breed purebred, inbreeding, outcrossing, grading up – Cross breeding • Mating animals of different breeds two-breed cross, three-breed cross, rotation Systems of Breeding
  159. 159. Illustration of DNA Double Helix from Wikipedia. • An animal of a particular breed • Both parents are purebred Purebred Breeding
  160. 160. Illustration of DNA Double Helix from Wikipedia. Characteristics of the breed 1. Eligible for registry in breed association 2. Tend to be genetically homozygous 3. Specialized business
  161. 161. Illustration of DNA Double Helix from Wikipedia. • Mating related animals • Linebreeding and Closebreeding refer to how closely related the animals are • Requires a careful program of selection and culling • Expensive • Used most often by Universities for experimental work and Seedstock producers that provide animals for crossbreeding herds Inbreeding
  162. 162. Illustration of DNA Double Helix from Wikipedia. • Animals are very closely related and can be traced back to more than 1 common ancestor • Examples: – Sire to daughter – Son to dam – Brother to sister
  163. 163. Illustration of DNA Double Helix from Wikipedia. 1st Mating • A (Male) X B (Female) F1 • ½ A ½ B 2nd Mating • A • 1/2A 1/2B F2 • 3/4A 1/4B Example
  164. 164. Illustration of DNA Double Helix from Wikipedia. • Mating animals that are more distantly related • Can be traced back to 1 common ancestor • Examples – Cousins – Grandparents to grand offspring – Half-brother to half-sister • Increases genetic purity • Several generations results in desirable and undesirable genes to become grouped together with greater frequency—making culling easier Linebreeding
  165. 165. Illustration of DNA Double Helix from Wikipedia. 1st Mating • A x B • A x C F1 • ½ A ½ B • ½ A ½ C 2nd Mating • 1/2A1/2 B x 1/2A/2C F2 • ½ A ¼ B ¼ C Example
  166. 166. Illustration of DNA Double Helix from Wikipedia. • Mating animals from two different lines of breeding within a breed • Purpose is to bring together desirable traits from different lines • Experience is the best guide to use when line crossing Linecrossing
  167. 167. Illustration of DNA Double Helix from Wikipedia. • Mating of animals of different families within the same breed • Animals are not closely related • Purpose is to bring into the breeding program traits that are desirable but not present in the original animals • Used most by purebred breeders • Popular because it reduces the chances of undeniable traits are still present • Sometimes used in inbreeding programs to bring in needed traits Outcrossing
  168. 168. Illustration of DNA Double Helix from Wikipedia. • Mating purebred males to grade females • Good way to improve quality • Less expensive • Use of purebred sires long enough will eventually lead to the amount of grade breeding left in the offspring being less than 1% Grading Up
  169. 169. Illustration of DNA Double Helix from Wikipedia. 1st Mating • A1 x G F1 • 1/2A:1/2G • 50% Pure 50% Grade 2nd Mating • A2 x ½ A1 ½ G F2 • ½ A2 ¼ A1 ¼ G • 75% Purebred 25% Grade 3rd Mating • A3 x ½ A2 ¼ A1 ¼ G F3 • ½A3 ¼A2 1/8A1 1/8G • 87.5% Purebred, 12.5% Grade Example
  170. 170. Illustration of DNA Double Helix from Wikipedia. • Mating two animals of different breeds • Offspring is a Hybrid • Usually results in improved traits because dominant genes mask undesirable recessive genes • Superior traits that MAY result from crossbreeding are called heterosis Crossbreeding (X)
  171. 171. Illustration of DNA Double Helix from Wikipedia. • Good record keeping is essential • Calving difficulties may increase when crossing large breed sires with small breed dams • Fewer calving problems if large breed dams are used • Large breed dams have higher maintenance costs • Artificial insemination allows access to better bulls • To avoid inbreeding more than 1 breeding pasture may be required General Considerations Regarding Beef Crossbreeding Systems
  172. 172. Illustration of DNA Double Helix from Wikipedia. • Terminal Sire Crossed with F1 Females • Rotate Herd Bull every 3-4 years • Two Breed Rotation • Three Breed Rotation • Four and Five Breed Rotation • Static Terminal Sire • Rotational Terminal Sire • Composite Systems Beef Crossbreeding Systems
  173. 173. Illustration of DNA Double Helix from Wikipedia. • Replacement crossbred (F1) females in the herd are purchased and crossed with a terminal bull. • All offspring are sold. Rotate Herd Bull Every 3-4 Years • Same breed of bull is used for years and then replaced with a bull of a different breed. • Replacement females are selected from the herd. Terminal Sire Crossed with F1 Females
  174. 174. Illustration of DNA Double Helix from Wikipedia. • Bulls from Breed A are crossed with cows from Breed B. • Resulting heifers are bred to bulls from breed B for the duration of their productive life. • Replacement heifers from that cross are bred to bulls from breed A. • Each succeeding generation of replacement heifers is bred to a bull from the opposite breed used to sire the replacement heifer. Two-Breed Rotation
  175. 175. Illustration of DNA Double Helix from Wikipedia. F Parents Offspring Genes Heterosis (approx. %) L E female male 1 L E LE 50 50 100 2 LE L L/LE 75 25 50 3 L/LE E E/(L/LE) 37 63 75 4 E/(L/LE) L L/[E/(L/LE) 69 31 62 5 EL E EEL 34 66 63 Rotational crossing using two breeds
  176. 176. Illustration of DNA Double Helix from Wikipedia. • Same pattern of breeding as the 2 breed rotation except that a bull from a 3rd breed is used in the sire rotation. 3 Breed Rotation
  177. 177. Illustration of DNA Double Helix from Wikipedia. • Larger herds • Bulls from a 4th or 5th breed may be used in the rotation of sires • This system requires a higher level of management and record keeping than 2 and 3 breed systems. 4 and 5 Breed Rotations
  178. 178. Illustration of DNA Double Helix from Wikipedia. Genera tions Parents Off-spring Genes Heterosis Female Male L A B 1 L A LA 50 50 100 2 LA B B/LA 25 25 50 50 3 B/LA L L/(B/LA) 63 12 25 75 4 L/B/LA A A/{L/(B/LA)} 32 56 12 62 5 ETC B ETC 16 28 56 32 6 ETC L ETC 58 14 28 84 Heterosis-in three crossbreeding After many generations, the breed will settle down to ratio of 4:2:1
  179. 179. Illustration of DNA Double Helix from Wikipedia. • 4 breeding groups • Group 1 (25% of the herd) mates breed A bulls to breed A cows to produce replacement heifers for group 1 and group 2. • Group 2 (25% of the herd) breeds the AA heifers to a bull (breed B) to a different breed, producing crossbred heifers (breed AB) • Group 3 (50% of the herd) breeds the AB heifers to a terminal (T) bull selected for its ability to transmit a high rate of gain. Static Terminal Sire System
  180. 180. Illustration of DNA Double Helix from Wikipedia. • A subgroup (Group 4, 10% of the herd) of the 3rd group is composed of AB heifers being bred for the first time. These AB heifers are bred to a smaller breed (breed C) bull to reduce 1st time calving problems. • All the male offspring of groups 1 and 2 and all offspring of groups 3 and 4 are sold. • Any heifers from groups 1 and 2 that are not kept for breeding are also sold.
  181. 181. Illustration of DNA Double Helix from Wikipedia. • Two breeding groups needed • Bulls from breeds A and B are used on a rotating basis on 50% of the herd providing crossbred females for the entire herd • Mature cows in the herd are mated with a terminal bull to produce offspring, all of which are sold. • Replacement females come from mating of bulls A and B with younger cows in the herd. Rotational –Terminal Sire System
  182. 182. Illustration of DNA Double Helix from Wikipedia. • Developing a new breed based on crossbreeding 4 or more existing breeds of cattle to avoid inbreeding problems • After development the composite breed is not crossbreed with other breeds Composite Breeds
  183. 183. Illustration of DNA Double Helix from Wikipedia. Livestock Breed Composition Dairy cattle Australian Milking Zebu Jamaica Hope Karen 0.33 Sahiwal + red Sindi/0.67 Jersey o.8 Jersey/0.05 Friesian/0.15 Sahiwal Brown Swiss/Sahiwal Beef cattle Bonsmara Chabray Santa Gertrudis Renitole (of madagascar) 0.62 afrikander/0.19 hereford + 0.19 Shorthorn 0.6Charolais/0.38 brahman 0.62 Shortorn/0.38 Brahman 3-breed cross malagasy zebu+ Limousin + Afrikander Sheep Dorper Katahdin Perendale Dorset Horn/Blackhead Persain Virgin Island/ Wiltshire Horn + Suffolk Goats Boer Local with European, Angora and Indian blood
  184. 184. Illustration of DNA Double Helix from Wikipedia. Breed Wt, 2.5 years kg Weaning % Weaning weight (Kg) Calf Per Cow* Afrikander(AF) 339 51.4 174 89.4 Angoni (AN) 285 65.1 149 97.0 Barotse (BA) 311 53.8 163 87.0 Boran (BO) 329 64.5 169 109.0 AVERAGE OF CROSSES AN X BA 302 61.8 158 97.6 AN X BO 312 69.1 160 110.6 BA X BO 340 65.9 173 114.0 Breed and crossbred means (reciprocal crosses) for Various traits of cattle in Zambia
  185. 185. Illustration of DNA Double Helix from Wikipedia. • 2 basic breeding systems—straight and crossbreeding • The type of system used depends on: the size of the operation, the amount of money available and the goal of the producer • Purebred animal are eligible for registry and tend to be genetically homozygous • Inbreeding increases the genetic purity of livestock but generally reduces performance. It is not generally used by the average producer but rather by those that do experimental work to improve the breed. Summary
  186. 186. Illustration of DNA Double Helix from Wikipedia. • Outcrossing brings genetic traits into the breeding program that tend to hide undesirable traits • Crossbreeding is the mating of animals from two different breeds, it is used by many commercial producers and usually results in hybrid vigor. This improves some traits but all little effect on feed efficiency and carcass traits.
  187. 187. Illustration of DNA Double Helix from Wikipedia. • Occurs when two individuals share the common ancestor or ancestors; • Mating of close related animal can either deliberate or accidental • More likely to occur i. in small, self-contained herds flock than in large population ii. Small numbers of males Inbreeding
  188. 188. Illustration of DNA Double Helix from Wikipedia. Systems of Mating: the rules by which pairs of gametes are chosen from the local gene pool to be united in a zygote with respect to a particular locus or genetic system.
  189. 189. Illustration of DNA Double Helix from Wikipedia. Systems of Mating: A deme is not defined by geography but rather by a shared system of mating. Depending upon the geographical scale involved and the individuals’ dispersal and mating abilities, a deme may correspond to the entire species or to a subpopulation restricted to a small local region. The Hardy- Weinberg model assumes one particular system of mating – random mating – but many other systems of mating exist.
  190. 190. Illustration of DNA Double Helix from Wikipedia. Some Common Systems of Mating: • Random Mating • Inbreeding (mating between biological relatives) • Assortative Mating (preferential mating between phenotypically similar individuals) • Disassortative Mating (preferential mating between phenotypically dissimilar individuals)
  191. 191. Illustration of DNA Double Helix from Wikipedia. Inbreeding: One Word, Several Meanings Inbreeding is mating between biological relatives. Two individuals are related if among the ancestors of the first individual are one or more ancestors of the second individual.
  192. 192. Illustration of DNA Double Helix from Wikipedia. • Inbreeding Can Be Measured by Identity by Descent, Either for Individuals or for a Population (Because of shared common ancestors, two individuals could share genes at a locus that are identical copies of a single ancestral gene) • Inbreeding Can Be Measured by Deviations from Random Mating in a Deme (either the tendency to preferentially mate with relatives or to preferentially avoid mating with relatives relative to random mating)
  193. 193. Illustration of DNA Double Helix from Wikipedia. Identity by Descent Some alleles are identical because they are replicated descendants of a single ancestral allele
  194. 194. Illustration of DNA Double Helix from Wikipedia. Properties of Assortative Mating • Increases the Frequency of Homozygotes Relative to Hardy-Weinberg For Loci Contributing to the Phenotype Or For Loci Correlated For Any Reason to the Phenotype • Does Not Change Allele Frequencies – • Assortative Mating Creates Disequilibrium Among Loci that Contribute to the Phenotype and Is A Powerful Evolutionary Force at the Multi-Locus Level • Multiple Equilibria Exist at the Multi-Locus Level And The Course of Evolution Is Constrained By the Initial Gene Pool: historical factors are a Determinant of the course of evolution
  195. 195. Illustration of DNA Double Helix from Wikipedia. Disassortative Mating occurs when individuals with dissimilar phenotypes are more likely to mate than expected under random pairing in the population
  196. 196. Illustration of DNA Double Helix from Wikipedia. Disassortative Mating as an Evolutionary Force • Is a powerful evolutionary force at the single locus level, generally resulting in stable equilibrium populations with intermediate allele frequencies and f<0 • It is less powerful as an evolutionary force at the multi-locus level because it produces a heterozygote excess, which allows linkage disequilibrium to break down more rapidly • Mimics the heterozygote excess of avoidance of inbreeding, but unlike avoidance of inbreeding, it affects only those loci correlated with the relevant phenotype, and it causes allele frequency change.
  197. 197. Illustration of DNA Double Helix from Wikipedia. And now it’s time for…. • Spongebob Genetics!!!!!

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