The lineage of pea plants produced round seeds for four generations. The plants that fertilized these pea plants also produced round seeds. However, in the fifth generation, the plant produced to two plants with wrinkled seeds. Can that be possible?

Yes, it is possible.

In this case both of the parental plants were heterozygotes and they manifested dominant allele in their phenotype, which is round seed.

P: Aa x Aa

F5: AA, Aa, aA, aa - possible genotypes in fifth generations.

A - dominant allele (round seeds); a - recessive allele (wrinkled seeds)

Wrinkled phenotype is manifested only if there are two recessive alleles present.