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X-linked defects are very common

X-linked defects are very common Among males of European ancestry, 8% have a protan or deutan defect. 15% of females are carriers. X n X p. X n Y. X p Y. X n X p. X n X n. X n Y. X p Y. X n X n. X n X p. X n Y. X p X p. X p Y. X n Y. X n X p. X n X p. -. c. a. r. r. i. e.

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X-linked defects are very common

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  1. X-linked defects are very common Among males of European ancestry, 8% have a protan or deutan defect. 15% of females are carriers.

  2. XnXp XnY XpY XnXp XnXn XnY XpY XnXn XnXp XnY XpXp XpY XnY XnXp XnXp - c a r r i e r - a f f e c t e d m a l e - n o r m a l m a l e - a f f e c t e d f e m a l e - n o r m a l f e m a l e Inheritance Pattern

  3. Sharpe & Jägle, 2001

  4. L/M Gene Array 1) Head-to-tail tandem array on the X chromosome, 2) L and M genes are highly homologous, 3) Susceptible to unequal homologous recombination.

  5. Normal Array Normal Array Deutan Array Protan Array Unequal crossovers generate color deficient genotypes

  6. The L and M genes are proposed to have arisen from duplication of an ancestral color pigment gene. If the genes were allowed to intermix from the beginning, how could they ever have diverged in the first place?

  7. Variation in the pigment genes can only come about by passing through a color defective genotype!!! Selection against color vision defects would block the generation of normal variation keep the L and M genes at separate loci.

  8. The generation of color vision deficiencies and the generation of normal variants are intimately related.

  9. Normal Array Normal Array Deutan Array Protan Array

  10. Normal Array Deutan Array Normal Array Deutan Array

  11. Normal Array Normal Array Deutan Array Protan Array

  12. Normal Array Deutan Array Normal Array Deutan Array

  13. Deutan Normal Deutan Normal Deutan Normal Number of Crossovers 1 2 3 4 5 6 0 Phenotype

  14. 3 general causes of congenital red-green color vision defects 1) L or M gene is missing (single- or multi-gene L/M array) 2) Mutation in the L or M gene makes the opsin non-functional (e.g., it isn’t folded properly or doesn’t get transported) 3) Gene present, but not expressed (position in the gene array or possible promoter mutation)

  15. MM - Protanope NC - Deuteranope Missing all L gene(s) Has “normal” gene array Dichromat with “missing” cones Courtesy Joe Carroll, Heidi Hofer & David Williams, U. Rochester Jay & Maureen Neitz, Medical College of Wisconsin

  16. protan deutan

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