Question

Red–green color blindness is a human X-linked recessive disorder. The normal allele (XB) is dominant to the mutant allele (Xb). Jill has normal color vision, but her father is color blind. Jill marries Tom, who also has normal color vision. Jill and Tom have a daughter who has Turner syndrome and is color blind. How did the daughter inherit color blindness?
A. Paternal nondisjunction followed by fertilization by sperm carrying sex chromosomes Xb

B. Maternal nondisjunction followed by fertilization by sperm lacking sex chromosomes

C. Paternal nondisjunction followed by fertilization by sperm lacking sex chromosomes

D. Maternal nondisjunction followed by fertilization by sperm carrying Xb

E. Maternal nondisjunction followed by fertilization by sperm carrying XB

Answer 1

Answer:

C

Explanation:

Turner Syndrom individuals have an aneuploidy (Cells with abnormal chromosome numbers), their sex cells only have one X chromosome.

Paternal genetic apportation is, in this case, XB (Because Tom has normal vison), Jill genotipic is XBXb (Color Blindness is recessive, Xb is not expressed on her fenotipic because the dominant XB make her has normal vision).

Tom only has sperm carrying XB chromosomes because he has normal vision.

Jill Ovules are XB or Xb, She has both alleles.

An Jill's ovule carring the Xb mutante allele is fertilized by sperm lacking sex chromosomes. As a result their Daughter is born withTurner Syndrom and Color Blindness.

This sperm lacking sex chromosomes is the result of a Paternal nondisjunction of sex chromosomes during meiosis

"Bonus"

As color blindness is a X-linked recessive disorder, this case is one of the fewer scenarios when Jim and Tom can have a Daughter with Color Blindness. In a normal case  their outspring has these possibilities of having Colorblindness...

 Genetic Cross

       Jill x Tom

 (XBXb x XBY0)

Genotipic             Fenotipic

XBXB 25%    Females with normal vision

XBXb 25%    Females with normal vision    

XBY0 25%    Males with normal vision

XbY0 25%    Males with Color Blindness

75% of their children will have normal vision

100% of females will have normal vision

50% of males will have normal vision

Only males, 50% of them, will have Color Blindness.