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Fundamentals of Genetics

Fundamentals of Genetics. I. Introduction to Genetics. 1. Gregor Mendel - “Father of Genetics” Austrian monk, teacher, scientist, gardener Formulated basic laws of heredity in the early 1860s. 2. Worked with garden peas because: Easy to grow and had a short generation time

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Fundamentals of Genetics

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  1. Fundamentals of Genetics

  2. I. Introduction to Genetics 1. Gregor Mendel - “Father of Genetics” • Austrian monk, teacher, scientist, gardener • Formulated basic laws of heredity in the early 1860s

  3. 2.Worked with garden peas because: • Easy to grow and had a short generation time • Could be self-pollinated 3. Chose varieties that were true-breeding • No genetic variation for a trait 4. Studied 7 simple traits

  4. 5. Mendel cross-pollinated plants • P= parental generation • F1= first-generation (sons/daughters) • F2 =second-generation

  5. 6. Principle of Dominance and Recessiveness • F1 plants resembled only one of the parents • F1hybrids contained two different factors (alleles) for each trait • one dominant;(masks recessive); • one recessive; (seems to disappear)

  6. Which are you?

  7. 7. Principle of Segregation • Organism contains two factors for each trait. • Alleles separate from one another during formation of gametes. • Each gamete contains one allele for each trait.

  8. 8. Principle of Independent Assortment • Each trait is independent of another • Genes of one pair of traits assort independently • All combinations of genes occur in gametes

  9. II. Chromosomes, Genes, & Genetic Crosses • Homologous Chromosomes contain genes (locations on DNA for traits) for the same traits • Traits are controlled by alleles (alternative forms of a gene). 3. Genotyperefers to the alleles an individual receives at fertilization 4. Phenotyperefers to the physical appearance of the individual.

  10. 5. Homozygous dominantgenotypes = two dominant alleles for a trait. (BB) 6. Homozygous recessivegenotypes = possess two recessive alleles for a trait (bb) 7. Heterozygous genotypes= one of each allele for a particular trait (Bb) Review: True-breeding organisms would be homozygous dominant OR recessive individuals. Hybrids would be heterozygous

  11. 8.Punnett Squares • Show probabilities of future offspring. • A monohybrid cross = cross between individuals that involve 1 contrasting trait.

  12. 9. Monohybrid Crosses Examples Ex. 1: One is heterozygous for round seeds x one with wrinkled seeds R r Phenotype/Genotype Chart R r r r r Phenotype Genotype(s) Round RR & Rr Wrinkled rr R r r r r Plant #1’s genotype: Plant #2’s genotype: Rr rr Genotype probability:______________ Genotype ratio:___________________ Phenotype probability:_____________ Phenotype ratio:__________________

  13. T T T t t Tt Tt TT Tt T t Tt Tt t Tt tt B. Example 2 & 3: P & F1 cross for true-breed tall x true breed short Tall TT, Tt Short tt P cross F1 cross Phenotype Genotype(s) 25% pure tall 50% hybrid tall 25% pure short 100% Tall 100% Heterozygous (Homozygous x Homozygous) (Heterozygous x Heterozygous)

  14. End for today

  15. Complete and diagram the 3 types of monohybrid crosses below. • Round peas are dominant to wrinkled peas. Cross a homozygous dominant x homozygous recessive. • Short plants are recessive to tall plants. Cross a homozygous recessive x heterozygous • Green peas are dominant to yellow peas cross a heterozygous x heterozygous

  16. Round peas are dominant to wrinkled peas. Cross a homozygous dominant x homozygous recessive. Phenotype Genotype(s)

  17. 2. Short plants are recessive to tall plants. Cross a homozygous recessive x heterozygous Phenotype Genotype(s)

  18. 3. Green peas are dominant to yellow peas cross a heterozygous x heterozygous Phenotype Genotype(s)

  19. 10. Test Crosses • A cross of an individual of unknown genotype with an individual of known genotype.(has to be homozygous recessive) • Results tells if unknown individual is heterozygous or homozygous • Very important to breeders

  20. I. Beyond Mendel 1. Incomplete dominance • Offspring are intermediate between two parental phenotypes • Neither allele is completely dominant over the other • Both alleles influence phenotype • 3 phenotypes

  21. Ex: Japanese Four o’clocks RR = red RR’ = pink R’R’ = white R R R R’ R’ R’ RR’ RR’ RR RR’ R R’ RR’ RR’ RR’ R’R’ All Pink 1 red : 2 pinks : 1 white

  22. 2. Codominance • Both alleles of a gene are expressed. • A person with AB blood has both A and B antigens on their red blood cells. • Neither allele is dominant or recessive

  23. P1 generation cross

  24. Brown WHITE Both Brown and white expressed at the same time. ROAN

  25. Ex: Red Coat - RR White Coat – WW White & Red Mixed – RW (“roan”) R R R W RW RW RW R W RR W W RW RW RW WW All Roan – both red and white hair 1 red : 2 roan : 1 white

  26. 3. Multiple Allele Traits are traits with 3 or more alleles; only get 2 1. ABO Blood group system; types – A, B, AB, O 2. IAIA=type A IAi= type A ii = type O IBIB= type B IBi= type B IAIB= type AB • *A,B codominant *Both dominant to O

  27. What are the possible blood types when a Person with AB blood and a person that is homozygous for B blood reproduce? Type A IAIA , IAi Type B IBIB , IBi Phenotype Genotype(s) Type AB IAIB Type O ii IA IB IB IAIB IBIB Type AB & B are possible IBIB IAIB IB

  28. What are the possible blood types when a Person with homozygous A blood and a person that is homozygous for B blood reproduce? Type A IAIA , IAi Type B IBIB , IBi Phenotype Genotype(s) Type AB IAIB Type O ii IA IA IB IAIB IAIB Type AB only IAIB IAIB IB

  29. What are the possible blood types when a Person with B blood and a person with O blood reproduce? Type A IAIA , IAi Type B IBIB , IBi Phenotype Genotype(s) Type AB IAIB Type O ii IB i IBi ii i i IBi ii

  30. End of the notes today! • Any questions?

  31. RrYy X RrYy Law of Independent Assortment: • Genes for different traits are inherited independently • R, r, Y, y go to sperm/egg independently of each other • Can recombine in four ways: Ry RY RrYy rY ry

  32. A = feathers C = crest Genotypes aa AA, Aa Genotypes AACC, AACc, AaCC, AaCc AAcc, Aacc aaCC, aaCc aacc Phenotypes Blue feathers Red feathers Phenotypes Red feathers, w/ Crest Red feathers, w/o Crest Blue feathers, w/ Crest Blue feathers, w/o Crest 3. Dihybrid Cross: A cross involving two pairs of contrasting traits Phenotypes w/ Crest w/o Crest Genotypes CC, Cc cc

  33. Example Cross P1:RRYY xrryy yellow, round green, wrinkled (homozygous) (homozygous) RY RY RY RY Offspring are all heterozygous ry RrYy RrYy RrYy RrYy RrYy RrYy ry RrYy RrYy RrYy ry RrYy RrYy RrYy ry RrYy RrYy RrYy RrYy

  34. 9 Round seeds are dominant to wrinkled and yellow is dominant to green. What are all the possible phenotypes? round, yellow: round, green : wrinkled, yellow: wrinkled ,green: 3 3 RrYy X RrYy 1 Phenotypic Ratio is 9:3:3:1 Ry rY ry RY RY RRYY RRYy RrYY RrYy Ry RRYy RRyy RrYy Rryy rY RrYY RrYy rrYY rrYy ry RrYy Rryy rrYy rryy

  35. End of the notes today! • Any questions?

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