Final answer:
The statement that affected parents always have affected offspring in dominant inheritance is false because an affected heterozygous parent can pass on the recessive allele to their offspring.
Step-by-step explanation:
The statement 'In dominant inheritance, affected parents always have affected offspring' is false. Dominant inheritance means that all affected individuals have at least one dominant allele, but this does not guarantee that all offspring will be affected.
An affected parent can have unaffected offspring if the parent is heterozygous for the trait and passes on the recessive allele. For instance, if we consider pea plants as an example, if both parents are heterozygous (carrying one dominant and one recessive allele for a trait), there is a 25% chance for any given offspring to be homozygous recessive and, therefore, not express the dominant trait.
Moreover, in human genetics, chance plays a significant role in inheritance. For a disease like cystic fibrosis, which follows autosomal recessive inheritance, two carriers can have offspring without the disease because each child has an independent chance of inheriting either allele.
In the case of Mendelian genetics, a heterozygous dominant organism (like a plant with one dominant and one recessive allele for flower color) is able to mask the recessive trait, resulting in offspring with a dominant phenotype. However, inheritance of such traits doesn't always follow expected ratios in smaller populations or families.