Explain how the backbone of DNA is constructed from nucleotide building blocks. A. DNA's backbone is not constructed from nucleotide units.

B. Nucleotide building blocks use covalent bonds to attach to one another at their sugar and phosphate ends.

C. Nucleotides use hydrogen bonds to attach themselves to the backbone.

D. Nitrogen bases use hydrogen bonds to attach to one another across the center of the molecule.

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Apuppy’s tendency to chew is inherited through which of the following? a. through learned behavior b.through genes c. through seasonal cycles d. through hibernation

Explain why scientists use the word dominant for certain traits.

Which of the following is an advantage of using embryonic stem cells in medical research? a. the use of embryonic stem cells is much less expensive than the use of adult stem cells. o b. no living tissue is damaged when scientists use embryonic stem cells. o c. embryonic stem cells are able to differentiate into a wider range of cells than adult stem cells. d. there is no controversy surrounding the use of embryonic stem cells.