Arrange the steps in the correct order to explain how a muscle fiber contracts. myosin and actin protein filaments attach to each other. calcium ions release into the myofibrils. myosin filaments pull on the actin filaments. the nerve impulse reaches the neuromuscular junction. the motor neuron carries the nerve impulse. the sarcomere shortens. ↓ ↓ ↓ ↓ ↓

The motor neuron carries the nerve impulse.

↓

The nerve impulse reaches the neuromuscular junction.

↓

Calcium ions release into the myofibrils.

↓

Myosin and actin protein filaments attach to each other.

↓

Myosin filaments pull on the actin filaments.

↓

The sarcomere shortens.

The neurotransmitter (ACh) from motor neurons signals a muscle fiber to depolarize. The depolarization (Na+) will trigger Ca++ release and will initiate contraction by binding to troponin. Myosin pulls the actin strands. ATP sustains the contraction.

c) 50% there are four chromosomes. after crossing over, 2 of the four have been changed. that means any gamete has a 2 in 4 chance or 50% chance of receiving the mutated chromosome.