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Genetics

Genetics. Modified by Georgia Agricultural Education Curriculum Office July 2002. Genetics. Is the science of heredity. Heredity is the transmission of genetic or physical traits from parent to offspring. Gregor Mendel. Austrian Monk Considered the “Father of Heredity”

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Genetics

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  1. Genetics Modified by Georgia Agricultural Education Curriculum Office July 2002

  2. Genetics • Is the science of heredity. • Heredity is the transmission of genetic or physical traits from parent to offspring.

  3. Gregor Mendel • Austrian Monk • Considered the “Father of Heredity” • He conducted plant breeding experiments in their monastery garden. • In 1865 he made his work public, units of inheritance.

  4. What makes us unique? • Each of the 100 Trillion cells in our body except the red blood cells contains the entire human genome, in the nucleus of every cell is the genetic information “blueprint” to construct the individual. • It is the Deoxyribonucleic acid (DNA) • Function of DNA • Genetic code for almost every organism. • Provide template for protein synthesis.

  5. Composition of DNA • The structure of DNA was discovered by Watson and Crick in 1953. • It is a twisted double helix molecule, containing sugar, phosphates, and nitrogenous bases. • The sugar is deoxyribose and the phosphoric acid molecules are always the same and provides for the structure (side of the ladder). • The only difference between us is the order and arrangement of the four bases (rungs of the ladder).

  6. Bases of DNA • Adenine= A • Thymine= T • Guanine= G • Cytosine= C • A always pairs with T • C always pairs with G

  7. Bases of RNA • Adenine= A • Uracil= U • Guanine= G • Cytosine= C • G always pairs with C • T from the DNA = A in the RNA • A from the DNA = U in the RNA

  8. DNA Model

  9. Chromosomes • The DNA in every cell is located in rod like segments called chromosomes • Chromosomes occurs in pairs in every cell of our body except in the sperm and ovum. • Chromosomes numbers are the same for each specie.

  10. Chromosome Numbers Species Diploid # Haploid # Cattle 60 30 Swine 38 19 Sheep 54 27 Horse 64 32 Human 46 23 Chicken 78 39 Goat 60 30 Donkey 62 31

  11. Chromosomes • There are 2 sex chromosomes included in the diploid number of the chromosomes. • All of the other chromosomes are referred to as autosomes. • In mammals if the sex chromosomes are alike, XX it results in a female. • If the sex chromosomes are different, XY it results in a male.

  12. Sex Determination • Females contribute an X chromosome towards the sex of their offspring. • Males can contribute an X or a Y chromosome toward the sex of their offspring. • Absence of an Y chromosome results in a the embryo developing into a female. • Presence of an Y chromosome results in the embryo developing into a male.

  13. Sex Determination • Gametogenesis = Formation of gametes through meiosis. • Male = 4 viable spermatids • Female = 1 viable ovum, 3 polar bodies.

  14. Tell me what I am ?????

  15. Tell me what I am ?????

  16. Cell Division • Meiosis • Is the form of cell division which results reducing the chromosome number from the diploid # to the haploid #. • Occurs only in the sex cells, sperm and ovum. • Mitosis • Is the form of cell division which results in the formation of identical daughter cells, keeps the chromosome number constant. • Tissue growth and repair. • Occurs throughout the body except in the sex cells.

  17. Genotype or Gamete • Genotype contains two copies of the gene. • AaBB • Gamete (sex cells) contains only one copy of the gene. • AB • Determine the possible gametes of AaBB • AB aB

  18. Gamete or Genotype • State if its a gamete or genotype. • Aa • D • DdEeFFgg • sRtxyq • AaBBeeFF • adgEFT

  19. List all the possible gametes. • From the genotype AaBb • AB • Ab • aB • ab

  20. Genes • Chromosomes contains several units of inheritance “genes”. • Genes usually occurs in pairs, one from each parent. • Some traits are inherited directly from one set of genes. • Some traits are inherited through several sets of genes.

  21. Genes • It was presumed that we were composed of about 100,000 genes to construct us. • Today, research has proven that number is a lot less than 100,000. • Extra credit for the student that can find an article about the current number of genes.

  22. Terms to know • Homozygous- contains 2 identical genes for the same trait, AA, BB, cc • Heterozygous- contains 2 different genes for the same trait, Aa, bB, Cc • Phenotype- Outward appearance of a trait, coat color, polled, horned. • Genotype- Genetic classification of a gene, AA, Aa, aa. • Allele- Location of a gene on the chromosome. • F-one = First cross mating. • F-two = Second cross mating.

  23. What are dominant genes? • The gene that express itself, the powerful and dominant gene. • It has the power to overshadow the recessive gene when there is complete dominance. • Some examples are: • White faced in cattle • Droopy ears in swine • Polled in cattle • Black coat color in Angus cattle

  24. What are Recessive Genes? • The gene that is overshadowed by a dominant gene • Recessive genes can only express themselves in the absence of the dominant gene • Polled vs Horned (Pp) (pp) • Black wool vs white (Ww) (ww) • Dwarfism vs normal size (dd) • Albino

  25. Punnet Square • Angus- Black coat color is dominant. • BB = Homozygous Dominant and Black • Bb = Heterozygous and is black • bb = Homozygous recessive and red • A heterozygous bull is mated to 50 homozygous recessive cows. • How many calves are black? • How many calves are red? • What is the genotypic and phenotypic ratios?

  26. Punnet Square

  27. Results • 2 heterozygous = Bb • 2 Homozygous Recessive bb • 25 Black, 25 Red • Genotypic ratio = 0:2:2 • Phenotypic ratio = 2 Black: 2 Red

  28. What are Sex Linked Genes? • Some recessive genes are attached to the X and Y chromosomes • Humans: Colorblindness and Baldness are on the X chromosomes • In Men, traits expressed anytime present • In Women, must have two recessives to show trait • Children get baldness from mothers

  29. If Dad is bald, will you be bald?

  30. Baldness is carried by the mother

  31. What if Mom is bald?

  32. What is Incomplete Dominance? • If both genes express themselves • Shorthorn Cattle: Red male mated to a White female = Roan calf • RR crossed rr = Rr

  33. Punnet Square • Shorthorn Cattle • RR = Red • rr = white • Rr = roan • If a red bull (RR) is mated to a white cow (rr), what color will the calves be?

  34. Shorthorn: Red X White

  35. Punnet Square • If a red bull (RR) is mated to a roan (Rr) cow, what color will the calves be?

  36. Shorthorn: Red X Roan

  37. What if Both Parents are Roan?

  38. What is a Mutation? • Dramatically different from what is expected genetically • Horned calf from polled parents • Loss of some or extra body parts • Lethal Mutation: causes death at birth • Sublethal Mutation: limits animals ability to grow to maturity • Beneficial Mutation: loss of tail in lambs

  39. What is Heritability? • Chance that traits will be inherited • Low: multiple births, fat covering • Medium: birth wt, wean wt, milk, wool grade, carcass wt, rate of gain • High: Loin eye area, fleece length & quality

  40. Mating Systems • Upgrading: mating purebreds with grade animals • Inbreeding: mating closely related animals • Linebreeding: mating distantly related animals • Outcrossing: mating unrelated animals in the same breed. • Crossbreeding: mating animals of same species but different breeds.

  41. What is Hybrid Vigor? Heterosis • Offspring will outperform either of the parents • Corn Breed A yields 100 bu/acre • Corn Breed B yields 100 bu/acre • Crossbreed A & B yields corn that yields 200 bu/acre • Vigor only expressed in crossbreeding

  42. The End

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