What are two processes that must occur to form soil?
a. weathering breaks rocks into minerals and plants die and decay.
b. erosion and weathering
c. plants produce loam and plants produce humus
d. erosion transports mineral particles and plants die and decay

genetic variation can be caused by mutation (which can create entirely new alleles in a population), random mating, random fertilization, and recombination between homologous chromosomes during meiosis (which reshuffles alleles within an organism's offspring).

nucleic acid molecules are incredibly complex, containing the code that guarantees the four different nucleotide units comprise dna, the nucleic acid of interest to the genealogist. and one of four nitrogen-containing molecules called nucleotides