Which of the following describes a benefit of membership in a research community?
a. several related measurements are entered into a single database.
b. knowledge and valuable resources are shared among scientists.
c. an experiment is repeated several times to verify the results.
d. multiple forms of evidence are used to support a conclusion.

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.