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Inheritance & Gene Expression
Advanced Principles Answers

Advanced Principles Review Answers:

     1. D - A phenotypically type O child has a genotype of OO; therefore, each parent must supply one of the O alleles. A father with genotype AB could not satisfy this requirement.

     2. B - Males are affected much more often than females by sex-linked traits due to their heterozygous condition in regards to the sex chromosomes.

     3. D - The Human ABO Blood System is an example of multiple alleles controlling phenotypic expression of a trait.

     4. G - Hemophilia and Color-blindness affect more males than females because they are both X-linked conditions; therefore, males only need one recessive allele to have the condition. Males are also affected more often by male-patterned baldness due to the presence of testosterone.

     5. D - The A and B alleles of the Human ABO Blood System are codominant. O, however, is recessive to both A and B.

     6. B - Male patterned baldness is a sex-influenced trait; therefore, the gene is found on an autosome but its expression is influenced by sex hormones.

     7. G - Both skin color and eye color are examples of polygenic traits.

     8. B - There is a 25% chance, at the highest, that their child will have Type A blood.
          B       O
A    AB    AO
B    BB    BO

     9. B - There is a 25% chance, at the highest, that their child will be a daughter with color-blindness.
           X^N = Normal Vision
           Xⁿ = Color-blindness

               X^N          XⁿXⁿ     X^NXⁿ       XⁿXⁿ
Y       X^NY         XⁿY

     10. B - There is a 25% chance, at the highest, that their child will be a son with normal vision and blood type AB.

              X^N          X^NXⁿ     X^NXⁿ       X^NXⁿ          50% chance
Y       X^NY         X^NY

            B       B
A    AB    AB                        50% chance
B    BB    BB

The product rule must now be applied to find the combined chance of these two events occurring together.
               (1/2)*(1/2) = 1/4 = 25%

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