A group of individuals that can mate with each other and produce fertile offspring.
A group of individuals that are completely geographically isolated from other groups.
A group of individuals all of which have the same general appearance and body plan.
Liligers -- the offspring of a lion and a liger, which is the offspring of a lion and a tiger.
Mules, the sterile offspring of a horse and a donkey.
Every individual carries two versions (alleles) of the gene for any trait. When parents pass on these traits by producing gametes, they pass on one copy at random, and the offspring ends up with its own combination of one gene copy from each parent.
Every individual carries one version of the gene for any trait. When parents pass on their genes to offspring, the offspring get their version of the gene from one parent, or the other, randomly.
Every individual carries two versions of the gene for any trait. When parents pass on these traits they always pass on the "dominant" version which means that the offspring look like their parents unless there is a mutation.
X-ray diffraction produces spots that are reflected from the electrons in the molecule. The "Maltese Cross" pattern seen in Franklin's data looked like diffraction patterns from other helices. Watson and Crick went to work with balls, sticks and wires and built a physical model of DNA that could correctly fit a helical model.
X-ray diffraction produces spots that are reflected from the electrons in a molecule. Watson and Crick were able to analyze these reflections and triangulate between them to figure out the exact positions of atoms in the DNA double helix.
X-ray diffraction works something like a photograph of the molecule. The regular pattern that they saw was a representation of the regularly arranged DNA base pairs in the molecule.