most are formed when a plant or animal dies in a watery environment and is buried in mud and silt.
Answer:
new cells come only from existing
Answer:
AB, Ab, aB, ab.
Explanation:
Crossover may be defined as the process of exchange of the genetic material between the non sister chromatids of two homologous chromosomes. This process occurs at the prophase I of meiosis.
The one chromosome carries A and B genes and the homologous chromsome carries same genes, a and b. The single cross over has occur so two parental gametes are formed (AB, ab) and two gametes are recombinant (aB and Ab).
Thus, the answer is AB, Ab, aB, ab.