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I need help with this biology question I am confused in the gene part?Marian’s father...

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chinee91 | (Level 2) eNoter

Posted November 8, 2012 at 2:40 AM via web

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I need help with this biology question I am confused in the gene part?

  1. Marian’s father is colorblind, as is her maternal grandfather (her mother’s father). Marian herself has normal color vision. Marian and her husband, Martin, who is also colorblind, have just had their first child, a son they have named Mickey. What is the probability that this child will be colorblind, and why?

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trophyhunter1 | College Teacher | (Level 3) Senior Educator

Posted November 29, 2012 at 1:34 PM (Answer #1)

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Marian is a carrier for the colorblindness allele. A female gets one X from her mother and one from her father. Since her father is colorblind, his X chromosome has to contain the colorblind allele. Therefore she is a heterozygote. Colorblindness is linked to the X chromosome. Let's call X the symbol for normal vision and X* the symbol for colorblindness. Marian's genotype is XX*. When Marian and Martin have children, she is XX* and Martin is X*Y. His Y chromosome has no role in the transmission of colorblindness genes. Male children get their X chromosome from their mother and the Y from their father. There is a 50:50 chance for their male children to have colorblindness or normal vision. If X from the mother and Y from the father combine, this produces a normal vision male (XY). If the X* and Y combine, this produces a colorblind male(X*Y). Martin being colorblind has no effect whatsoever on his son's vision. It is the mother's X chromosome that affects male children.

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alphadav | Student, Undergraduate | (Level 1) Valedictorian

Posted November 21, 2012 at 12:04 PM (Answer #2)

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1)  the probability is zero 

2) none of the three persons contribute for the colourblindness of mickey.

3) refer th below link

4) this will not change as a male cannot pass colourblindness  to his son as disease is sex (X-chromosome) linked and father contributes only Y-chromosome for his son. 

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