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Punnett square


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Punnett square

  1. 1. Genetics
  2. 2. What is Genetics? • All body cells contain “Blueprints” with instructions as to how an animal will look or act etc. • One Gene comes from each parent (pairs) • Genes are divided into sections (Chromosomes) that carry genes • Sex chromosomes: male = XY, female = XX
  3. 3. What are Dominant Genes? • Dominant Genes = one gene overshadows the other • Angus Cattle: black is dominant, red is not (Bb) • Hereford: white face is dominant (Ww) • Hampshire Hog: white belt is dominant • Horns are dominant (Pp)
  4. 4. What are Recessive Genes? • The gene that is overshadowed by a dominant gene • Recessive genes can only express themselves if both genes are recessive • Polled vs Horned (Pp) (pp) • Black wool vs white (Ww) (ww) • Dwarfism vs normal size (dd) • Albino
  5. 5. Punnet Square • P = horned • p = polled • If a homozygous horned cow (PP) is mated to a homozygous polled bull (pp), what percent of the calves will be horned, polled?
  6. 6. Punnet Square P P p Pp Pp p Pp Pp
  7. 7. Punnet Square • If a homozygous horned cow (PP) is mated to a heterozygous horned bull (Pp), what percent of the calves will be polled?
  8. 8. Punnet Square P P p Pp Pp p Pp Pp
  9. 9. 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
  10. 10. What is Incomplete Dominance? • If both genes express themselves • Shorthorn Cattle: Red male mated to a White female = Roan calf • RR + WW = RW
  11. 11. Punnet Square • Shorthorn Cattle • R = Red • W = white • RW = roan • If a red bull (RR) is mated to a white cow (WW), what color will the calves be?
  12. 12. Shorthorn: Red X White R R W RW RW W RW RW
  13. 13. Punnet Square • If a red bull (RR) is mated to a roan (RW) cow, what color will the calves be?
  14. 14. Shorthorn: Red X Roan R R RR R RR W RW RW
  15. 15. What if Both Parents are Roan? R R W RR RW W RW WW
  16. 16. 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
  17. 17. What is an Abnormality? • Similar to a Mutation, only it is caused by something in the environment • Siamese twins
  18. 18. 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
  19. 19. Heritability • Currently have ewes that wean 70 lb lambs • Want to raise weaning wt to 110 lbs • Select a ram with a wean wt of 110 lbs • Heritability of weaning wt is 30% • What can you expect new lamb crop to weigh at weaning?
  20. 20. Heritability • What is the difference in current weaning wt and that of the new ram? 110 - 70 = 40 lbs • Heritability % x difference 30% x 40 = 12 lbs • Can expect a gain in weaning wt of 12 lbs • 70 lbs + 12 lbs = 82 lbs
  21. 21. What is Hybrid Vigor? • 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 • Donkey mated to a horse = Mule – mule is sterile
  22. 22. Genetic Terms • Genotype: genetic makeup (Bb) • Phenotype: physical appearance (Black) • Heterozygous: Genes are different, Dominant & Recessive (Bb) • Homozygous: both genes are the same (BB or bb)