What is used to make a linkage map for a group of organisms? the number of traits one gene set can control in the group
the number of phenotypes a gene set can produce in the group
the number of times linked genes are separated in the group
the number of different genes found in the group

answer: the blood-brain barrier is a layer of specialized membranes and cell processes designed to keep undesirable substances from passing from the bloodstream into the precious tissues of the brain. while the blood-brain barrier does keep most bad things out of the central nervous system, it is not impermeable.

explanation:

enhanced global partnerships and exploration capabilities may advance international preparedness for protecting the earth from catastrophic events such as some asteroid strikes, advancing collaborative research on space weather and protecting spacecraft by developing new means for space debris removal.

sound moves fastest in solids because the molecules are tightly packed and it allows sound to vibrate