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1. Red-green colour blindness is sex linked. (Unless otherwise stated, ‘sex linked’...

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tchrome | eNoter

Posted June 10, 2013 at 10:21 PM via web

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1. Red-green colour blindness is sex linked. (Unless otherwise stated, ‘sex linked’ refers to a gene located on the non-homologous portion of the X chromosome.) The allele for red-green colour blindness is recessive to the allele for normal vision. a)A normal sighted woman, whose father was red-green colour blind, married a man with normal vision. What ratios of genotypes and phenotypes would be expected among their children? b)Under what circumstances would all the daughters of a marriage have normal vision and all the sons be red-green colour blind?

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tjbrewer | Elementary School Teacher | (Level 2) Associate Educator

Posted June 11, 2013 at 12:48 AM (Answer #1)

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1a.  We can find the Genotypes of phenotypes of the children by using a Punett Square C:dominant gene for normal vision, c: recessive color-blindness, y: male gene w/o an allele for vision. 

    C   y
c  Cc  cy
C CC  Cy

This tells us that 1/4 children will be color-blind and those will all be boys. 
The other 1/2 of the boys will have normal vision from their mother.  The girls will all have normal vision but 1/2 will be carriers of the gene. 

1b.  We can reverse engineer the Punett square to solve this one.

     C?  cy
     C?  cy

This leads us to

     C    y
  c Cc  cy
  c Cc  cy

The Father has normal vision, and the mother is color blind.  All the girls will inherit dad's normal vision, but the boys won't because it's not on the y-chromosome. 

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