Someone wrote:

>But since positive blood types are dominant, more frequently than not
>the baby is positive.

Frequency and dominance are not related.  An allele can be dominant but not
frequent (the allele for Achondroplastic dwarfism) or it can be recessive
but most common (the O allele on the ABO blood-group system).

It is true that Rh+ allele combinationss are both dominant and more frequent
than Rh- allele combinations.

There are two ways to be Rh+, either ++ or +-.

If an Rh- mother (--) is married to a homozygous Rh+ father (++), then all
of her babies will be Rh+ (+-).

If an Rh- (--) mother is married to a heterozygous Rh+ father (+-), then 50%
of her babies will be Rh+ (+-) and 50% of her babies will be Rh- (--).

Kathy Dettwyler




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