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Genetics PowerPoint Presentation

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Slide 1-

Genetics
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Phenotype is what an animal looks like Phenotype = Genetics + Environment (+GxE interactions) Genotype = the genetic makeup of the organism Phenotype/Genotype
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Gregor Mendel Ahead of that time there was no good concept of transmission of genetic information from one generation to the next. Discovery of Genetics
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Austrian Monk lived 1823-1884 Presented his observations and experiments on pea plants in 1865 Discoveries lay unnoticed ~20 years until others independently found the same thing He found traits were controlled by discrete “factors” (genes) Gregor Mendel
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All plants & animals are made of small building blocks called cells Cells composed of: cell wall nucleus cytoplasm All cells originate from other cells Cell Theory of Inheritance
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Gene Genes are particular parts of DNA Contained in the NUCLEUS Unit of Inheritance
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DNA Deoxyribonucleic Acid Contains the genetic code by the arrangement of 4 base pairs. Up to 600/gene Structure of DNA by Watson & Crick won Nobel prize
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DNA Made up of 4 nucleotides and deoxyribose Forms genes Genes reside on chromosomes
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Chromosomes Made up of DNA Contain many genes on each chromosome Not always visibile, only when they coil up Occur in pairs in somatic cells
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1 pair of chromosomes determines sex Other traits on that chromosome will be “sex linked” traits Mammals Female = XX Male = XY (different nomenclature for poultry) Sex
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Homozygous SAME Heterozygous DIFFERENT Some Terms
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Homologous = “member of pair” Dipoid = 2n number of chromosomes Haploid = 1n number of chromosomes More Terms
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Dominance = gene always expressed Recessive = gene only expressed if not masked Codominant or Lack of Dominance = both homologous genes expressed More more terms
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Angus - Black is dominant, Red is recessive Shorthorn - Red, White, No Dominance, All patterns, Roan
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Locus = Location on the chromosome of a gene Allele = alternate genes that occupy corresponding sites on homologous chromosomes like black and red for angus cattle More more more terms
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Kinds of cell division Mitosis The way cells divide in somatic cells Results in diploid # of chromosomes Meiosis Cell division in sex cells (ova, sperm) Results in haploid # of chromosomes Even MORE Terms
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Mitosis 1- Interphase 2- Prophase 3- Metaphase 4- Anaphase 5- Telophase
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Reduction division Occurs only in gametes (sex cells) Results in 1/2 the # of chromosomes (haploid number) 1 of each pair of homologous chromosomes Meiosis
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Horse 64 Donkey 62 Mule 63 Swine 38 Sheep 54 Cattle 60 Man 46 Mink 30 Dog 78 Lion 38 Domestic cat 38 Bengal tiger 38 Chicken 78 No. of Chromosomes by Species
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Explains the segregation and recombination of genes Understandable for a small number of traits at a time Understandable for traits controlled by 1 or a few genes MOST Productivity traits = many genes Mendellian Genetics
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Mutation Accidental change in the structure of a gene Occur with low frequency randomly or from radiation, chemicals, drugs, etc. Abnormalities
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Mutation types- Crossing Over
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Mutation types - Deletion
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Mutation types - Duplication
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Mutation types - Insertion
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Usually BAD Sometimes NO EFFECT Sometimes GOOD Polled condition in hereford cattle Are Mutations Good or Bad?
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When traits are controlled by single gene pairs, predicting phenotype from genotype is possible if we know the type of gene action! Dominance Recessive Codominance Prediction
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More useful is predicting the GENOTYPE from what we see of the animals (phenotype) We can make matings and observe the outcome ONLY finds Statistical Probability in some cases
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View now the genetic animations for determining the combinations possible!
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Most economically important traits involve several or many genes Growth depends on appetite, gut capacity, metabolism rate etc etc etc Milk production depends on mammary development, cow size, appetite, blood supply, etc etc etc etc Livestock Improvement
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Goal is to select animals with many good genes Remember P = G + E So to compare animals, keep the Environment the same Therefore -- Population Genetics
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Have maximum genetic variation Spend selection efforts on traits largely influenced by heredity Observe (measure) accurately the traits carried by the animal Use the selected animal(s) most effectively Rules for Maximum Genetic Improvement
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Uniformity may be good, but limits genetic progress Breeding herds exist to provide best genetics for future generations (and improve) 1. Have maximum genetic variation
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Heritibility h2 The proportion of variation that can be expected to be transmitted to the next generation The relative importance of heredity in influencing certain traits Heritability refers to TRAITS not the animal 2. Spend selection efforts on traits largely influenced by heredity
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Cattle Swine No. of young weaned 10-15 10-15 % lean cuts 40-50 30-40 Rate of gain 50-55 25-30 Heritability estimates
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Low (5-15%) Reproductive traits Health Medium (15-40%) Conformation score (dairy, beef 25%) Many production characteristics High (40%+) Carcass characteristics Growth rate (cattle, sheep) Mature weight Level of Heritability
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Depends on how much better the parents are than the average of the population. Two parents, each has ½ the influence Depends on the heritability of the trait Progress = selection differential * h2 How much progress can we make?
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How much better are the parents than the average of the population they are selected from Selection differential
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Say herd population is 18,000 lbs of milk Choose a bull with a milking potential of 22,000 lbs of milk Choose cows with 20,000 lbs milking potential Bull Cow 22,000 20,000 -18,000 18,000 ---------- ---------- 4,000 2,000 ½ the genetics comes from bull, ½ from cow So you can have ½ of 4000 and ½ of 2000 Example
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½ the genetics comes from bull, ½ from cow So you can have ½ of 4000 and ½ of 2000 (4000 + 2000) / 2 = 6000/2 = 3000 Multiply the Selection Differential (3000) by h2 H2 for milk production is 0.25 3000 X 0.25 = 750 lbs of improvement Add that to the herd avg: 18,000 + 750 = 18,750 Which is the avg of production in the replacements. Example
Slide 45-

If the replacements = 10% of the herd, What is the new herd average? 90% of herd still averages 18,000 10% of herd averages 18,750 (18,000)(.90) + (18,750)(.10) = 18,075 If we replace 20% of the herd (18,000)(.80) + (18,750)(.20) = 18, 150 Example
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As you can see, progress is slow So you must continue to strive to make progress as steadily as you can
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The selection differential on the bulls side is the same (22000 – 18000 = 4000) Sel.Diff. On the cow side is 0 4000 / 2 = 2000 (2000 X .25) = 500 which is improvement Add 500 to herd average (500 + 18000) = 18,500 If you only selected the bull
Slide 48-

Suppose a swine herd average is 1.2 inches of backfat Select a boar with 0.8 inches, gilts with 1.0 in. (1.2 – 0.8) = 0.4 (1.0 – 0.8) = 0.2 (0.4 + 0.2) / 2 = 0.3 The offspring are expected to be 0.3 better 1.2 inches – 0.3 inches = 0.9 avg of next generation Let’s do another example
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Amount of genetic variation Heritability Accuracy of measurement of information Extent of use of selected animal What influences how much genetic progress you can make?
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Prolificness Two years selection in corn could produce 327,680 Billion descendants for planting from 2 kernels selected Swine have bigger litters than cattle How extensively you can make use of an animal is influenced by:
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Generation time Poultry completes a generation in 7 or 8 months Sows farrow first at 1 year of age, 2 litters/year Cow calves first at 2 or 3 years, say avg of 5 yrs as a realistic practical average With long generation interval comes slower rate of improvement How extensively you can make use of an animal is influenced by:
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Desirable traits Health Prolificness Regular heat periods, enough ova, conceive on 1st service Males masculine and progressive, sufficient volume, concentration of sperm Long life, longevity (in some animals) Cows more impt than pigs 3. Observe/measure accurately the traits carried by the animal
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Efficient growth Quality of product Desirable traits, continued
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Choose traits contributing most to long-term profit Choose traits for which your herd is lacking Choose traits with a degree of heritability Factors that influence which traits to emphasize
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Records Individuals, birth dates, litter size, birth weight Use a SCALE, not eyeball Proper ID of animals Carcass measurements Backfat, loin eye area, carcass length, etc. Measure accurately
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Tatoo Ear notch Ear tag Leg band Brand Freeze brand Paint Animal Id Systems
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Records are best Other methods Teeth Size of body parts Age estimation
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Use of Central Testing facilities Pros Cons
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Systems for measuring meatiness Backfat probe (fat depth related to meatiness) Metal ruler Ultrasonics “Fat-o-meter” TOBEC Cutout info from relatives Visual appraisal – OFTEN INACCURATE
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Sperm volume, concentration, viability Libido Scrotal circumference In the female, it may be more difficult to assess Mothering ability Temperament Ways of assessing breeding efficiencies of sires beforehand
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Some of the “desired” terms are highly unscientific Need adequate leg structure, mammary system, etc. Some traits cannot be easily measured Conformation
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Realize selecting for many things means less progress in each Selection Thresholds vs Indexes Indexes take into account relative economic importance and heritability How to consider multiple traits
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Ancestors Animal gets just ½ its genes from a parent Is ¼ related to a grandparent Only 1/8 related to a great grandparent Sibs (brothers & sisters) Progeny Relatives
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The BEST info on what genes an animal can pass into its offspring is what is seen in its offspring Progeny Testing
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When you want the best answer badly Because it takes a long time to develop a parent (long generation interval) Expensive procedure Use for Dairy cattle, Beef cattle Less used for poultry, swine Use of offspring selected on other info can make more rapid progress even if less accurate When to progeny test
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Will sow with large litter 1 have another? Does production repeat in next season? Depends on the trait Repeatability
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Trait Beef Sheep Swine Prolificacy .10 Birth wt .30 .30 Repro Effic. .10 .20 .10-.16 Weaning wt. .45 .40 Grade at wean .22 Annual wool .50-.60 Repeatability
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AI Embryo transfer Use the selected animal most effectively
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Increased vigor of crossbreds as compared with the average of the purebred parents High for “non-additive” traits Maternal ability Survival Low for : carcass, growth rate Hybrid Vigor = Heterosis
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Can NOT be transmitted from one generation to the next MUST be recreated in each generation by making the cross Heterosis
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How important? Everybody? Forever? Heterosis
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Random mating Selected males and females run together Example: bulls with cows in range country Inbreeding Mating relatives Used to concentrate genes (homozygosity) Concentrates good genes AND bad genes Mating Systems
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Outbreeding Similar to crossbreeding, but still within a breed Mating animals that are “unrelated”
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Mating animals from different breeds Need a system to make progress successfully Reasons for crossbreeding Bring in good genes lacking in a breed Increase vigor, prolificacy Crossbreeding
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Rotational crosses 2 way 3 way How many breeds? Advantage – can produce your own females Crossbreeding methods
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Select a male line and a separate female line Sell all resulting offspring Purchase males, females Advantage: Male line can be great at carcass & doesn’t have to be great at maternal traits Female line can emphasize female traits Terminal Cross
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“Breeds” per se became less important in poultry, likely swine will follow Identification of specific genes of benefit Marker assisted selection Transgenics and other biotechnology tools “Genomics” Maybe “the future is now” The future