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Non-Mendelian Problems

Non-Mendelian Problems. I Sex-linked Traits. These are Traits (genes) that are located on the sex chromosomes. Sex chromosomes are X and Y XX genotype for females XY genotype for males Many sex-linked traits are carried on X chromosome of the sex chromosomes

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Non-Mendelian Problems

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  1. Non-Mendelian Problems

  2. I Sex-linked Traits • These are Traits (genes) that are located on the sex chromosomes. • Sex chromosomes are X and Y • XX genotype for females • XY genotype for males • Many sex-linked traits are carried on X chromosome of the sex chromosomes • That is why these genetic disorders are found mainly in males, there is no gene for this trait on the Y chromosome to cancel out a bad gene on the X chromosome

  3. fruit fly eye color Xy chromosome – male -the trait will be determined by the gene on the X, none On the Y XX chromosome - female Sex-linked Traits Example: Eye color in fruit flies Sex Chromosomes

  4. Xr Xr XR Y Sex-linked Trait Problem • Use the same principles used in the Mendelian Monohybrid problems, except that the sex of the offspring must be included and the Y chromosome will not have an allele • Example: Eye color in fruit flies • (red-eyed male) x (white-eyed female)XRY x XrXr • Remember: the Y chromosome in males does not carry traits. • RR = red eyed • Rr = red eyed • rr = white eyed • XY = male • XX = female

  5. POSSIBLE GENOTYPES IN SEX-LINKED PROBLEMS: XRXR—FEMALE w/ HOMOZYGOUS DOM XRXr—FEMALE w/ HETERZYGOUS XrXr—FEMALE w/ HOMOZYGOUS REC XRY—MALE w/ DOM ALLELE XrY—MALE w/ REC ALLELE

  6. Xr Xr XR Xr XR Xr XR Y Xr Y Xr Y Sex-linked Trait Solution: Genotypic Ratio: 50% XR Xr 50% Xr Y Phenotypic Ratio: 50 % white eyed male 50 % red eyed female

  7. Sex-linked Cross ?s from previous problem 1. What % of the males will be red eyed? 2. What % of the offspring will be red eyed? 3. What % of the offspring will be males? 4. What % of the females will be white eyed? 5. What % of the females will be red eyed? 6. What % of the offspring will be white eyed?

  8. Female Carriers *1/2 filled in box=carrier, filled in box=affected individual

  9. Incomplete Dominance

  10. W W R R Incomplete Dominance • F1 hybrids have an appearance somewhat in between the phenotypes of the two parental varieties. There is a mixing of the two traits, neither is dominant over the other. Worked like Monohybrid problems except that you will use all capitals letter for each trait, ex. Red=RR, white=WW Pink=RW • Ex:snapdragons (flower) • red (RR) x white (WW) • RW=pink flower • RR = red flower • WW = white flower *Fill in the square to the left

  11. W produces the F1 generation RW RW R R RW RW Genotypic Ratio: 0:4:0—100%RW Phenotypic Ratio: 0:4:0—100%pink Incomplete Dominance W

  12. Incomplete Dominance Problem: • In cattle when a red bull(RR) is mated with white(WW) cow the offspring are roan(RW) a blending of red and white. Mate a red bull with a roan cow. Use the format on the next slide and give the P1, do the Punnett Square, and give the genotypic and phenotypic ratios for F1 generation of this cross.

  13. P1 = __RR__ x __RW__ Genotypic ratio: ____ : _____ : _____ Phenotypic ratio: ____ : _____ : _____

  14. P1 = __RR__ x __RW__ R W R RR RW RW R RR 2 2 0 or 50%RR,50%RW Genotypic ratio: ____ : _____ : _____ 2 2 0 or 50%RED,50%ROAN Phenotypic ratio: ____ : _____ : _____

  15. Incomplete Dominance

  16. Dihybrid Cross • A breeding experiment that tracks the inheritance of two traits. • Mendel’s “Law of Independent Assortment” • a. Each pair of alleles segregates independently during gamete formation • b. Formula: 2n (n = # of heterozygotes)

  17. Question:How many gametes will be produced for the following allele arrangements? • Remember:2n (n = # of heterozygotes) • 1. RrYy • 2. AaBbCCDd • 3. MmNnOoPPQQRrssTtQq

  18. Answer: 1. RrYy: 2n = 22 = 4 gametes RY Ry rY ry 2. AaBbCCDd: 2n = 23 = 8 gametes ABCD ABCd AbCD AbCd aBCD aBCd abCD abCD 3. MmNnOoPPQQRrssTtQq: 2n = 26 = 64 gametes

  19. Dihybrid Cross • Traits: Seed shape & Seed color • Alleles: R round r wrinkled Y yellow y green RrYy x RrYy RY Ry rY ry RY Ry rY ry All possible gamete combinations by FOIL method

  20. RY Ry rY ry RY Ry rY ry Dihybrid Cross

  21. RY Ry rY ry Round/Yellow: 9 Round/green: 3 wrinkled/Yellow: 3 wrinkled/green: 1 RY RRYY RRYy RrYY RrYy Ry RRYy RRyy RrYy Rryy rY RrYY RrYy rrYY rrYy ry RrYy Rryy rrYy rryy 9:3:3:1 phenotypic ratio Dihybrid Cross

  22. Dihybrid Cross Round/Yellow: 9Round/green: 3wrinkled/Yellow: 3wrinkled/green: 1 9:3:3:1

  23. CODOMINANCE

  24. Multiple Alleles /Codominance • Non-Mendelian Cross where 2 alleles are expressed (multiple alleles) in heterozygous individuals. • Example: blood type Use the genotypes below whenever doing blood type crosses. • 1. type A = AA -pure or AO -hybrid • 2. type B = BB -pure or BO -hybrid • 3. type AB = AB -codominant • 4. type O = OO -pure

  25. IA i IAIB IBi IB Genotypic ratio: 50% IAIB Phenotypic ratio: 50% type AB 50%= IBi 50%= type B IB IAIB IBi Codominance Problem • Example: Cross a male who is homozygous Type B (BB) x a female that is heterozygous Type A (AO)

  26. IA IB i i Another Codominance Problem • Example: Cross a • male Type O (ii) x female type AB (IAIB) *Give the genotypic and phenotypic ratios of the offspring

  27. IA IB IAi IBi i Genotypic Ratio: 50% IAi Phenotypic Ratio: 50% type A 50% IBi 50% type B i IAi IBi Another Codominance Problem • Example:male Type O (ii) x female type AB (IAIB)

  28. 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)

  29. IA i IAIB IB i ii Codominance • Answer: Parents: genotypes = IAi and IBi phenotypes = A and B

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