Fundamental Principles of Genetics (Chapter 8)

1. Fundamental Principles of Genetics (Chapter 8) • Genetics – study of heredity • Gene – determinant of heredity • Chapter is outline of basic principles of genetics www.sardi.sa.gov.au/livestock/meat_wool/breeding_genetics

2. Plants and animals composed of cells • Plant cell – surrounded by cell wall • Animal cell – surrounded by cell membrane • Nucleus – location of chromosomes in cell • Chromosomes – carrier of genes Cell Theory of Inheritance

3. Carriers of genetic material – genes • Occur in pairs • Homologous chromosomes – members of a pair • Number of chromosomes constant among normal members of a species Chromosomes

4. Diploid (2N) numbers • donkey 62 horse 64 • mule 63 swine 38 • sheep 54 cattle 60 • human 46 mink 30 • dog 78 cat 38 • chicken 78 • Normal body cells have diploid (2N) number • Gametes (sperm and egg) have haploid (1N) number Chromosome Number

5. Two major types • Sex chromosomes – one pair which influences sex of organism • Autosomes – all pairs other than sex chromosomes • http://learn.genetics.utah.edu/content/begin/traits/karyotype/index.html Chromosomes

6. Mammals • Sex chromosomes are: • female XX homogametic • male XY heterogametic • Chickens and turkeys • Sex chromosomes are: • female ZW heterogametic • male ZZ homogametic Sex Determination

7. Changes in number of chromosomes (nondisjunction of sex cell) • Aneuploidy – extra or missing chromosome(s) • Polyploidy – extra sets of chromosomes • Usually lethal in animals • Except aneuploidy of very small chromosomes (eg Down Syndrome in humans is extra #21) Chromosomal Abnormalities

8. Changes in chromosome structure • (see fig. 8.3, p. 143 illustration) • Deletion – piece of chromosome removed • Duplication – piece of homologous chromosome duplicated • Translocation – exchange of material between different (nonhomologous) chromosomes • Inversion – segment of chromosome reversed Chromosomal Abnormalities

9. Changes in chromosome structure • Cause loss of fertility • Amount of loss dependent on type of change and importance of the affected segment of the chromosome • http://learn.genetics.utah.edu/content/begin/traits/karyotype/index.html Chromosomal Abnormalities

10. Two types • Mitosis – division of normal body cells • Meiosis – division of germinal cells to produce gametes (sperm and egg) Cell Division

11. Mitosis • Cell division of normal body cells • Each daughter cell has same genetic complement as original cell Cell Division

12. Mitosis • Four phases • Prophase • Metaphase • Anaphase • Telophase • Interphase – period between cell divisions Cell Division

13. Meiosis • Division in germinal cells to produce sperm and egg • Each cell that results has 1N number of chromosomes (half of number of chromosomes in body cells Cell Division

14. Meiosis • Two cycles of: • Prophase • Metaphase • Anaphase • Telophase • Results in four cells with 1N number Cell Division

15. Meiosis • During late prophase I • homologous chromosomes wrap together (synapsis) • Crossing over – exchange of genetic material between homologous chromosomes Cell Division

16. Meiosis • Spermatogenesis – meiotic production of sperm cells • Oogenesis – meiotic production of egg cells Cell Division

17. Check It Out! • http://www.dnaftb.org/

18. Component of DNA – deoxyribonucleic acid • Large double stranded polymer of units called nucleotides • Nucleotide • Sugar – deoxyribose • Phosphate group • Nitrogeneous base • adenine guanine • cytosine thymine The Gene

19. Bases in DNA code for transcription of RNA • RNA – ribonucleic acid • Also nucleic acid • Single stranded • Uracil instead of thymine • Ribose instead of deoxyribose Transcription of RNA

20. Three primary types of RNA • Messenger RNA • Transfers code from DNA to protein synthesis • Transfer RNA • Carries amino acids to the ribosome • Ribosomal RNA • Forms part of the structure of the ribosome RNA

21. RNA binds with ribosome • Ribosome is location of protein synthesis • Information on RNA used to generate amino acid sequence in proteins Translation of RNA

22. Each amino acid coded by a three base sequence (codon) • Most amino acids have more than one codon • One codon specifies beginning of a protein • Three codons specify the end of a protein Genetic Code

23. Complete gene is actually a complex of different types of genes (complex called an operon) • Structural genes • Code for actual protein sequence • Regulatory genes • Affect function of the structural genes Control of Gene Function

24. Epistasis • Two or more gene pairs (not alleles) in which one gene pair influences expression of another gene pair – may or may not be on homologs • Example: • Horned, polled, scurred • Two gene pairs (horned vs polled) (smooth vs scurred) • If horned – scurred vs smooth does not matter • If polled – scurred vs smooth can express Interactions Between Genes

25. After union of sperm and egg • Cell division occurs • Early development - all cells are alike • Subsequent development – cells differentiate • Embryological development is genetically controlled Genes and Embryological Development

26. Lethal genes • Genes which stop development • Many must be received from both parents to cause death • Cause of high percentage of embryonic death Genes and Embryological Development

27. Biotechnology • All technologies that pertain to molecular manipulation of living material • Very difficult word to characterize • Genetic engineering • New methods for modifying the animal genome Biotechnology

28. Recombinant DNA Technology • Segment of DNA removed from species of interest • Segment is inserted into a microorganism • Microorganism makes the product specified by the DNA • DNA is “recombined” into a new location Microbe Engineering

29. Used for production of: • Bovine growth hormone to increase milk production • Vaccines • Other pharmaceuticals • Bacteria to consume oil spills or other pollutants Recombinant DNA

30. Transgenesis • Movement of genes from one species into another • First use – development of mouse with extra genes for growth hormone Transgenesis

31. Round-up-ready crops • Several crop species have been engineered to be resistant to the herbicide Round-up • Bt crops • Corn and cotton have genes from a microbe that causes them to be resistant to corn borer and boll weevil • Flavr-Savr tomato • Gene altered to lengthen shelf life Genetic Engineering in Plants

32. Clone – genetic identical • Identical twins are clones • Cloning by embryo splitting has been available for several years • Cloning from an adult DNA donor not possible until “Dolly” Cloning

33. Dolly • Developed at Roslin Institute • Sheep cloned from cells from adult ewe mammary gland • Cells had to be “started over” to remove results of cell differentiation Cloning

34. Potential uses for cloning in animals • Limited importance in routine livestock improvement • Combine with transgenesis to produce animals with unique genetic makeup • transgenesis to create first copy of animal with specific gene inserted • cloning to make multiple copies of that animal Cloning

35. Current selection • Based on actual traits measured in animals • Marker assisted selection • Based on identification of genetic markers that are associated with performance traits • Can be applied as soon as appropriate tissue (blood, skin etc) can be obtained • Shortens time to obtain information for choosing superior parents Marker Assisted Selection

36. Genes occur in pairs (except for those on sex chromosomes which are sex-linked) • The segregation of genes (in body cells) at one locus (gene location) is normally independent of the segregation of genes (in gametes) at another location (Principle of Independent Assortment) • Exception to this rule when genes are linked (on same chromosome) Segregation and Recombination

37. Linkage • Genes tend to be inherited together if close together on same chromosome • Linkage relationships are broken by crossing over (exchange between homologous chromosomes) during meiosis I, prophase I • Basis for idea of Marker Assisted Selection – if genetic marker is linked with gene for trait of interest, can select based on the marker Segregation and Recombination

38. Mutation – change in the base sequence • May result in change in amino acid sequence in protein • May result in change in the phenotype • Change is usually detrimental (selection) • Only source of new genetic material Mutation

39. Phenotype = Genotype + Environment • Gene action varies among different genes • Dominance relationships vary widely Phenotypic Expression of Genes

40. Dominant and recessive • Color in Angus • Genotype Phenotype • BB Black • Bb Black • bb Red • Black is dominant to red • Red is recessive • BB or bb – homozygous • Bb - heterozygous Phenotypic Expression of Genes

41. Lack of dominance • Color in Shorthorns • Genotype Phenotype • RR Red • RW Roan • WW White • Both red and white are expressed in heterozygote Phenotypic Expression of Genes

42. Additive • Each gene substitution (A for a, B for b) contributes the same amount (each A or B “adds” the same amount (absolute?) • Example: skin color in humans • Livestock examples in Ch 9 • Contrast with non-additive types of gene action (dominance, epistasis) Phenotypic Expression of Genes

43. Genetic control of almost all traits is some combination of additive and non-additive • Allows use of selection to improve herds through increasing frequency of desirable genes • Allows use of crossbreeding to maximize efficient combinations of genes Phenotypic Expression of Genes

44. Some genes on the sex chromosomes • Inheritance pattern affected because males have only one X chromosome • Hemophilia in humans Sex-linked Inheritance

45. Inheritance that is affected by sex of individual • eg. scurs - dominant in males, recessive in females • eg. horns in sheep – dominant in males, recessive in females Sex-influenced Inheritance

46. Some traits express in only one sex • Female • Milk production, egg production, age at first estrus • Male • Scrotal circumference Sex-limited Inheritance

47. Human Genome project • Initiated by National Institutes of Health and Department of Energy • Large multi-year, multi-location project to map the human genome • Other genome projects • Cattle, sheep, swine, horses, dogs, cats, turkeys, chickens, mice and many other species Genome Project