In the lac operon, the repressor:a. binds to allolactose and becomes active, blocking lac gene expression. b. binds allolactose and binds to the promoter, and induces lac gene expression. c. binds to allolactose and becomes inactive, allowing lac gene expression to occur. d. binds to the promoter and blocks lac gene expression.

How are viruses different from eukaryotic cells?

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.

They live on every continent except antarctica