It is because when alleles show a co-dominant relationship , neither allele is dominant and both are expressed in the phenotype of the heterozygote. The human ABO blood groups provide a good example of codominace. The ABO system is due to a gene that codes for molecules on the surface of red blood cells
With each contraction cycle, actin moves relative to myosin. ... ATP can then attach to myosin, which allows the cross-bridge cycle to start again; further muscle contraction can occur. Therefore, without ATP, muscles would remain in their contracted state, rather than their relaxed state.
Answer:
Proteins is a macromolecule that helps to send signals
i pretty sure its Cytokinesis and Spindle Fibers.