Answers to Mendel's Problem III

Problem 1)
In a disputed parentage case the child is blood type O while the mother is blood type A. What blood type would exclude a male from being the father? Would the other blood types prove that a particular male was the father?

ANSWER
 The ABO blood groups are determined by 3 alleles I^A and I^B which are codominant and I^O which is recessive.

Blood Groups
 

Genotypes	IA	IB	IO
IA	A	AB	A
IB	AB	B	B
IO	A	B	O

The mother could have an  I^AI^O , or an I^AI^A genotype as her blood group is A.   A male with the  blood type AB carries  the alleles for both I^A and I^B, he cannot therefore carry the recessive allele I^O. As the blood group O is only found in I^OI^O individuals the child could not be from an AB father.
 The presence of other blood groups cannot prove a particular male could be the father since males with I^OI^O  or I^BI^O  or I^AI^O gentoypes could all produce I^OI^O progeny given that the mother also has two possible genotypes.
 

Problem 2)
In drosophila the X-linked recessive mutation vermilion (v) causes bright-red eyes in contrast to wild type brick-red eyes. A separate autosomal recessive mutation supressor of vermilion (s-v) causes flies homozygous or hemizygous for v to have wild type eyes. In the absence of the vermilion alleles s-v has no effect on eye colour.

 Determine the F1 and F2 phenotypic ratios of a cross between a female with wild-type alleles at the vermilion locus but homozygous for s-v, with a vermilion male who has wild-type alleles at the s-v locus.

ANSWER
    Parentel genotypes     normal female  X⁺ X⁺: s-v/s-v         vermilion male X^v/Y: s-v⁺/s-v⁺

    F1            ¹/₂ X⁺X^v:s-v⁺/s-v             normal female
                     ¹/₂ X⁺X^v:s-v⁺/s-v            normal male

    F2            ⁸/₁₆  wild type females
                    ⁵/₁₆  wild type males
                    ³/₁₆  vermilion males