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OUTLINE 14 VI. Extensions to Mendel’s Rules (continued) D. Sex Linked Inheritance

OUTLINE 14 VI. Extensions to Mendel’s Rules (continued) D. Sex Linked Inheritance 1. Sex chromosomes 2. Systems of sex determination a. XY system b. X0 systems c. ZW systems d. Haplo-diploid systems e. Non-chromosomalsex determination 3. X-linked inheritance

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OUTLINE 14 VI. Extensions to Mendel’s Rules (continued) D. Sex Linked Inheritance

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  1. OUTLINE 14 VI. Extensions to Mendel’s Rules (continued) D. Sex Linked Inheritance 1. Sex chromosomes 2. Systems of sex determination a. XY system b. X0 systems c. ZW systems d. Haplo-diploid systems e. Non-chromosomalsex determination 3. X-linked inheritance 4. Y-linked inheritance

  2. Application of Mendel’s Rules assumes: • 1. One allele completely dominates the other • 2. All genes have 2 allelic forms • 3. All traits are monogenic (affected by only one • locus) • 4. All chromosomes occur in homologous pairs • 5. All genes assort independently • 6. An allele is completely expressed when either • dominant or heterozygous • 7. Each trait is controlled by a different set of factors

  3. Hypothetical mechanism for determination of eye color in Humans Gene for melanin production B (produce) dominant to b (none) 2 Modifier loci affect amount of pigment deposited CC’ and DD’ each non prime allele contributes one unit of deposition G’type at B Modifier loci Phenotype B_ CCDD Dk brown (+4) B_ CCDD’ Med. Brown (+3) B_ CC’DD’ Lt Brown (+2) B_ CC’D’D’ Hazel (+1) BB C’C’D’D’ Green Bb C’C’D’D’ Greenish blue Bb any g’type Blue

  4. Hypothetical mechanism for determination of eye color in Humans A possible cross: P bbCCDD X BbC’C’D’D” (Blue) (Gr-blue) Gametes bCD BC’D’, bC’D’ F1 BbCC’DD” bbCC’DD’ (Lt. Brown) (Blue)

  5. XY sex determination In some plants

  6. Drosophila melanogaster

  7. XO sex determination

  8. ZW sex determination

  9. Haplo-diploid sex determination

  10. Parthenogenesis

  11. Environmental control Alligators Turtles

  12. Social control

  13. X Y

  14. Colorblindness: Alleles: X+ = normal vision, Xc = color blind (X+ is dominant) female genotypes male genotypes normal X+X+X+ Y color blind XcXcXc Y carrierX+Xc

  15. Females gametes Xc Xc X+ Male’s gametes Y

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