18. The individuals
who are shaded in the pedigree below represent individuals of a recessive trait.
The clear individuals could not be recessive, because then parents A & B
would be recessive & they could not have children D & E as dominant
children.
Rather, the shaded individuals are recessive,
the clear are dominant. This works as then parents A & B can then be heterozygous
dominant, which can give rise to recessive children as D or E.
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Slichter