Scientists developed the first successful human cell culture in vitro (grown in a lab) in the 1950s by removing cancer cells from a woman. this concept has allowed modern scientists to successfully grow organs. which of the following answers best determines why there was success? neurons send a signal to the cell to multiply. a large blood supply to the cell allows enough nutrients for growth. cells are the basic unit of life and thus can regenerate if in a controlled environment. cells cannot reproduce on their own, and the scientist manipulates them to grow.

During crossing-over, a. genetic material is exchanged between nonsister chromatids, resulting in new combinations of alleles. b. nonsister chromatids from each homologous chromosome of a tetrad are exchanged, resulting in new combinations of alleles. c. one homologous chromosome of a tetrad is exchanged with another tetrad, resulting in new combinations of alleles. d. sister chromatids from each homologous chromosome of a tetrad are exchanged, resulting in new combinations of alleles. e. genetic material is exchanged between sister chromatids, resulting in new combinations of alleles.