The Nervous System

Parts of the neuron

Signal or impulses,are electriacal signals are electrical impulse.
Impulses flash along individual nerve cell or neurons.
Each neuron have three main parts.A cell body dentrites and
an axon.Dentrites are a branching  nerve fiber that carry impulses

toward the cell body. An axon is a nerve fiber that carries impulses
away from the cell body.

Ehen an impulse reach the tip of an axon ,another nerve cell can`t
pick up directly.That`s beacuse there is a gap between neurons.
This gap is called a synapse and it is a only tiny fraction of an  inch wide.

Using What We`ve Learned

Human chromosomes carry genes that control a variety of traits.
Humans have 23pairs chromosomes. One of those pairs
determine the sex of a person.

Female inherited two X chromosomes, one from each parent.

Males inherited one X from one parent and one Y chromosomes from the other.
Only males have a Y chromosomes.

Inheritetance can be controlled by crossing plants or animals to produce offspring
with ceirtain deliberate trait. People have used selective breeding for centuries to produce
better crops, hardier domestic animals, and prettier flower.