Which of the following changes takes place during the second trimester of a
woman's pregnancy?
O A. The mother feels the fetus move for the first time.
B. The fetus begins rhythmic breathing movements.
C. The fetus's hands and feet appear
D. The fetus begins to form teeth.

Choose the best definition of allele. a. one of several possible versions of a gene, which each produce a different phenotype b. an organism that's purebred for a given trait c. the process of fertilizing a plant with pollen from another plant d. a set of genes that are located on the same chromosome and so are tightly linked