<em>The correct option is C) crossing over and independent assortment</em>
Explanation:
Crossing over and independent assortment can be described as the two essential phenomena of meiosis which brings genetic variations. During crossing over, the exchange of DNA segments between homologous chromosomes takes place. Independent assortment allows the chromosomes to assort independently into gametes hence bringing about the different genetic combinations. Hence, the correct option is C.
Other options, like option A, is false because chromosome inactivation will result in an abnormality.
Acetylcholine is a chemical that is found between the nerve synapses, or gaps, between nerve cells. When activated, it causes the contraction of skeletal muscles and activates glandular functions in the endocrine system. Think of acetylcholine as a mailperson; residents cannot receive their mail until he or she comes and delivers it to the mailbox. Like mailpersons who deliver the mail and move on to the next house, acetylcholine acts quickly and does not hang around. As a result, acetylcholine is rapidly broken down by another chemical substance called cholinesterase.
Acetylcholine was the first neurotransmitter scientists discovered, as well as the most abundant neurotransmitter in the body. A neurotransmitter is a chemical that is released by a neuron, or nerve cell, that sends a signal to another neuron across a synapse. The neurotransmitter binds to receptors to affect how the signal is received. The purpose of the neurotransmitter is to either amplify or inhibit the signals sent between the neurons.
Acetylcholine plays an important role in the signal of muscle movement, sensation of pain, learning and memory formation, the regulation of the endocrine system and rapid eye movement (REM) sleep cycles.
