Self-fertilization is avoided in sponges because
a. there is no way for sperm to enter the sponge.
b. the sperm do not possess the enzyme needed to penetrate the egg.
c. sperm and eggs are not produced at the same time.
d. none of the above is true; self-fertilization is common in sponges.

Which statement best describes the relationship between an allele and a gene? question 1 a. an allele is a variation of a gene that can be expressed as a phenotype. b. an allele is the part of a gene that attaches to messenger rna molecules. c. an allele is a segment of a dna molecule that controls replication of a gene.