Genetics

1. Genetics

2. Phenotype/Genotype • Phenotype is what an animal looks like • Phenotype = Genetics + Environment (+GxE interactions) • Genotype = the genetic makeup of the organism

3. Discovery of Genetics • Gregor Mendel • Ahead of that time there was no good concept of transmission of genetic information from one generation to the next.

4. Gregor Mendel • 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)

5. Cell Theory of Inheritance • All plants & animals are made of small building blocks called cells • Cells composed of: • cell wall • nucleus • cytoplasm • All cells originate from other cells

7. Unit of Inheritance • Gene • Genes are particular parts of DNA • Contained in the NUCLEUS

8. 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

9. DNA • Made up of 4 nucleotides and deoxyribose • Forms genes • Genes reside on chromosomes

10. 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

11. 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

12. Some Terms • Homozygous • SAME • Heterozygous • DIFFERENT

13. More Terms • Homologous = “member of pair” • Dipoid = 2n number of chromosomes • Haploid = 1n number of chromosomes

14. More more terms • Dominance = gene always expressed • Recessive = gene only expressed if not masked • Codominant or Lack of Dominance = both homologous genes expressed

15. Angus - Black is dominant, Red is recessive Shorthorn - Red, White, No Dominance, All patterns, Roan

16. More more more terms • 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

17. Even MORE Terms • 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

18. Mitosis 1- Interphase 4- Anaphase 3- Metaphase 2- Prophase 5- Telophase

19. Meiosis • Reduction division • Occurs only in gametes (sex cells) • Results in 1/2 the # of chromosomes • (haploid number) • 1 of each pair of homologous chromosomes

21. 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

22. Mendellian Genetics • 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

23. Abnormalities • Mutation • Accidental change in the structure of a gene • Occur with low frequency randomly or from radiation, chemicals, drugs, etc.

24. Mutation types- Crossing Over

25. Mutation types - Deletion

26. Mutation types - Duplication

27. Mutation types - Insertion

28. Are Mutations Good or Bad? • Usually BAD • Sometimes NO EFFECT • Sometimes GOOD • Polled condition in hereford cattle

29. Prediction • 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

30. 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

31. View now the genetic animations for determining the combinations possible!

33. Livestock Improvement • 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

34. Therefore -- Population Genetics • Goal is to select animals with many good genes • Remember P = G + E • So to compare animals, keep the Environment the same

35. Rules for Maximum Genetic Improvement • 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

36. 1. Have maximum genetic variation • Uniformity may be good, but limits genetic progress • Breeding herds exist to provide best genetics for future generations (and improve)

38. 2. Spend selection efforts on traits largely influenced by heredity • 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

39. Heritability estimates Cattle Swine • No. of young weaned 10-15 10-15 • % lean cuts 40-50 30-40 • Rate of gain 50-55 25-30

40. Level of Heritability • 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

41. How much progress can we make? • 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

43. Selection differential • How much better are the parents than the average of the population they are selected from

44. Example 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

45. Example 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.

46. Example • 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

47. As you can see, progress is slow • So you must continue to strive to make progress as steadily as you can

48. If you only selected the bull • 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

49. Let’s do another example • 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

50. What influences how much genetic progress you can make? • Amount of genetic variation • Heritability • Accuracy of measurement of information • Extent of use of selected animal