Why blood types many not be a great method of determining which baby belongs to which parent?

Question

Why blood types many not be a great method of determining which baby belongs to which parent?

Answer 1

There are two major problems with using blood type.

One problem is that there are often many possible blood types for the child, given the same pair of parents.  Try playing around with this calculator to get an idea:  http://www.biology.arizona.edu/Human_Bio...

The second problem is that blood type inheritance doesn't always follow simple genetics.  There are certain ways (Bombay phenotype, chromosome mixing) that mean that an "impossible" blood type can result with the child.

Answer 2

If the two parents in question have the same blood type, it is often difficult to determine paternity.

DNA analysis is much more reliable. But in the case of the polygamist compound where children of different mothers have the same father, and where there has been inbreeding for a generation or two, DNA analysis might have to be more detailed than in the usual case.