Genetics 2


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  • Mendelian Genetics 08/08/12
  • Mendelian Genetics 08/08/12
  • Mendelian Genetics 08/08/12
  • Mendelian Genetics 08/08/12
  • Mendelian Genetics 08/08/12
  • Mendelian Genetics 08/08/12
  • Mendelian Genetics 08/08/12
  • Mendelian Genetics 08/08/12
  • Mendelian Genetics 08/08/12
  • Mendelian Genetics 08/08/12
  • Mendelian Genetics 08/08/12
  • Mendelian Genetics 08/08/12
  • Mendelian Genetics 08/08/12
  • Mendelian Genetics 08/08/12
  • Mendelian Genetics 08/08/12
  • Mendelian Genetics 08/08/12
  • Mendelian Genetics 08/08/12
  • Mendelian Genetics 08/08/12
  • Mendelian Genetics 08/08/12
  • Genetics 2

    1. 1. Genetics
    2. 2. Heredity and Genetics • Heredity is the passing of traits from parents to offspring • Traits are controlled by genes, so GENETICS is the study of how traits are inherited through the action of alleles
    3. 3. Gregor Mendel – “Father of Genetics” • Austrian monk born in 1822 who is responsible for the laws governing the inheritance of traits • Between 1856 and 1863, Mendel cultivated and tested over 28,000 pea plants • Mendel performed cross- pollination by transferring pollen from one plant to selected ova of other plants, thereby controlling which plants mixed
    4. 4. Mendel’s Experiments• Mendel produced pure strains by allowing plants to self-pollinate, I.e., pollen (male gamete) from one plant fertilizes ova (female gamete) of same plant
    5. 5. Mendel’s Peas…. S s Y y I i G g
    6. 6. Mendel’s Peas…. P p A a T t
    7. 7. Mendel’s Results….(F2 from crossing to heterozygous F1s)
    8. 8. Genetics Terminology• Traits – any characteristic that can be passed from parents to offspring• Heredity – the passing of traits from parents to offspring• Alleles – one form (dominant or recessive) of a gene • Sex cells have ONE form of a gene on their chromosomes • Body cells have TWO forms or alleles for a single gene (you get one from mom and the other from dad) • Dominant – is always expressed; masks a recessive trait • Recessive – can only be expressed if there are no dominant alleles present
    9. 9. Genetics Terminology• Dominant alleles are represented by a capital letter• Recessive alleles are represented by a lower case letter Example: B = Brown eye color (dominant) b = Blue eye color (recessive)• “Purebred” species have two of the same alleles; this is also called HOMOZYGOUS, e.g., BB (homozygous dominant) or bb (homozygous recessive)• Species with two different alleles are called HETEROZYGOUS, e.g., Bb• Genotype: the alleles present in the organism, i.e., BB, Bb, or bb• Phenotype: the expression of the genes; what is observed
    10. 10. Genotype and Phenotype in Flower• All genes occur in pairs, so TWO alleles affect a trait.• Possible combinations if: R = Red flower r = Yellow flower• Genotypes RR Rr rr• Phenotypes Red Red Yellow
    11. 11. BrainPop - HeredityGenetic Crosses• Monohybrid Cross: cross involving ONE trait, e.g., eye color• Dihybrid Cross: cross involving TWO traits, e.g., eye color and hair color• Offspring’s genotype and phenotype is determined using a Punnett square B b B BB Bb b Bb bb
    12. 12. Punnett Square, cont.
    13. 13. Generations in Crosses• Parental Generation (P1) = the parental generation in a breeding experiment• First Filial Generation (F1) = the first generation of offspring in a breeding experiment• Second Filial Generation (F2) = the second generation of offspring in a breeding experimentTT tt Tt Tt TT Tt Tt tt
    14. 14. P1 Monohybrid Cross• Trait: Seed Color• Alleles: Y – Yellow y – Green• Cross: Yellow seeds X Green seeds YY X yy Crossing two true-breeding (pure) plants Y Y Genotype: Yy y Yy Yy Phenotype: Yellow Genotypic Ratio: 100% Yy Yy Yy Phenotypic Ratio: 100% Yellow y
    15. 15. F1 Monohybrid Cross• Trait: Seed Color• Alleles: Y – Yellow y – Green• Cross: Yellow seeds X Green seeds Yy X Yy Crossing to heterozygotes (hybrids) Y y Genotype: YY, Yy, yy Y YY Yy Phenotype: Yellow and Green Genotypic Ratio: 25% YY, 50% Yy yy Yy, 25% yy (1:2:1) y Phenotypic Ratio: 75% Yellow, 25% Green (3:1)
    16. 16. Dihybrid Crosses• A breeding experiment that tracks the inheritance of two traits• Mendel’s “Law of Independent Assortment” • Each pair of alleles segregates independently during gamete formation • Formula: 2n (n = # of heterozygotes) Example: 1. RrYy: 2n = 22 = 4 possible gametes RY Ry rY ry 2. AaBbCCDd: 2n = 23 = 8 gametes ABCD ABCd AbCD AbCd aBCD aBCd abCD abCD
    17. 17. Dihybrid CrossesTraits: Seed shape & Seed colorAlleles: R round r wrinkled Y yellow y green RrYy x RrYy RY Ry rY ry RY Ry rY ry All possible gamete combinations
    18. 18. Dihybrid Cross RY Ry rY ryRYRyrYry copyright cmassengale 18
    19. 19. Dihybrid Cross RY Ry rY ryRY RRYY Round/Yellow: 9 RRYy RrYY RrYyRy RRYy Round/green: 3 RRyy RrYy Rryy wrinkled/Yellow: 3rY RrYY RrYy rrYY rrYy wrinkled/green: 1ry RrYy Rryy rrYy rryy 9:3:3:1 phenotypic ratio copyright cmassengale 19
    20. 20. Dihybrid Cross Round/Yellow: 9 Round/green: 3 wrinkled/Yellow: 3 wrinkled/green: 1 9:3:3:1 copyright cmassengale 20
    21. 21. Test Cross•Test crosses involve breeding the individual inquestion with another individual that expresses arecessive version of the same trait. If alloffspring display the dominant phenotype, theindividual in question is homozygous dominant; ifthe offspring display both dominant and recessivephenotypes, then the individual is heterozygous Y Y Y yy Yy Yy y Yy yy Yy Yy Yy yyy y Offspring all yellow! ½ Offspring yellow; ½ Offspring green!
    22. 22. Test Cross• A mating between an individual of unknown genotype and a homozygous recessive individual.• Example: bbC__ x bbcc• BB = brown eyes• Bb = brown eyes• bb = blue eyes bC b___• CC = curly hair bc• Cc = curly hair• cc = straight hair copyright cmassengale 22
    23. 23. Test Cross Possible results: bC b___ C bC b___ cbc bbCc bbCc or bc bbCc bbcc copyright cmassengale 23
    24. 24. Incomplete Dominance and Codominance copyright cmassengale 24
    25. 25. Incomplete Dominance• F1 hybrids have an appearance somewhat in between the phenotypes of the two parental varieties.• Example: snapdragons (flower) red (RR) x white (rr) (rr r r RR = red flower R rr = white flower R copyright cmassengale 25
    26. 26. Incomplete Dominance r r produces theR Rr Rr F1 generationR Rr Rr All Rr = pink (heterozygous pink) copyright cmassengale 26
    27. 27. Incomplete Dominance copyright cmassengale 27
    28. 28. Codominance• Two alleles are expressed (multiple alleles) in heterozygous individuals.• Example: blood type• 1. type A = IAIA or IAi• 2. type B = IBIB or IBi• 3. type AB = IAIB• 4. type O = ii copyright cmassengale 28
    29. 29. Codominance Problem• Example:homozygous male Type B (IBIB) xheterozygous female Type A (IAi) IA i IB IAIB IBi 1/2 = IAIB 1/2 = IBi IB IAIB IBi copyright cmassengale 29
    30. 30. Another Codominance Problem• Example: male Type O (ii) x female type AB (IAIB) IA IB i IAi IBi 1/2 = IAi 1/2 = IBi i IAi IBi copyright cmassengale 30
    31. 31. Codominance• Question: If a boy has a blood type O and his sister has blood type AB, what are the genotypes and phenotypes of their parents?boy-type O (ii) X girl-type AB (IAIB) copyright cmassengale 31
    32. 32. Codominance • Answer: IA iIB IAIB Parents: genotypes = IAi and IBi phenotypes = A and Bi ii copyright cmassengale 32
    33. 33. Sex-linked Traits• Traits (genes) located on the sex chromosomes• Sex chromosomes are X and Y• XX genotype for females• XY genotype for males• Many sex-linked traits carried on X chromosome copyright cmassengale 33
    34. 34. Sex-linked Traits Example: Eye color in fruit flies Sex Chromosomes fruit fly eye colorXX chromosome - female Xy chromosome - male copyright cmassengale 34
    35. 35. Sex-linked Trait Problem• Example: Eye color in fruit flies• (red-eyed male) x (white-eyed female) Xr Xr XR Y x XrXr• Remember: the Y chromosome in XR males does not carry traits.• RR = red eyed Y• Rr = red eyed• rr = white eyed copyright cmassengale 35
    36. 36. Sex-linked Trait Solution: Xr Xr 50% red eyedXR X X X X R r R r female 50% white eyedY Xr Y Xr Y male copyright cmassengale 36
    37. 37. Female Carriers copyright cmassengale 37