Blood Types Problem Set

Problem 3: What blood type would the father be?

Help to answer the question

If the mother of a child is blood type O+ and the child is A-, what blood type would the father be? Does the Rh factor of the child being - mean that one of the parents has to be negative? Both of my parents are Rh - all of us siblings are Rh- as well. Could two Rh- parents give birth to a Rh+ child? and vice versa? Thanks for all your help. --MaryEllen

Tutorial

Blood types

The father has to be the source of the A allele of a child with blood type A, when the mother is of blood type O. The father could be type A or type AB. The types that can be ruled out for the father are type O and type B.

Mother's Possible Genotype	Child's Possible Genotypes	Father's Possible Genotypes
OO	AO	AA, AB

Rh factor

The Rh factor information doens't discriminate potential fathers of the child. Even though the child is Rh-, it is not necessary that either parent be Rh-.

The father of the child could be either Rh+ (heterozygous with one Rh+ allele and one Rh- allele) or Rh- (homozygous with two recessive Rh- alleles. )

When the mother is Rh- and the father is Rh+ (heterozygous with one Rh+ allele and one Rh- allele), there is a 50% probability for an Rh+ child and a 50% probability for an Rh- child.

When the mother is Rh- and the father is Rh-, as in the case of your own family, then all children (all of your siblings) will be Rh-.

Once again, if it is important to have correct and highly discriminating information about paternity, my advice would be to explore the possibility of a DNA-based paternity test. Although I cannot personally endorse any particular testing company, you may wish to visit the web page of a paternity lab at http://www.gentestlabs.com/

The Biology Project
University of Arizona
Thursday, October 23, 1997
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