As mentioned that the brain contains at least 100 billion neurons, more than a person needs, the brain going through rapid growth has transient exuberance which needs pruning. Why does the brain need to be pruned?

When old  or degraded neurons are removed and replaced  in the brain cells   so that  extra synaptic connections and axons  are removed, while stabilizing the needed ones the process is called brain pruning.

It ensures efficiency of synaptic connections.

It occurs in childhood and adulthood, and its occurs to maintain  neuronal  networks  in the brain through reduction in number of synapses and neurons.

Thus it is important in childhood to create new synaptic connections for the child's brain during development   to   create new  pathways for  complex  synaptic transmission  needed for child developments.

Explanation:

each of the 46 original chromosomes splits into two daughter chromosomes, so there are two sets of 46 daughter chromosomes that end up in each cell. human cells have 46 chromosomes. each chromosome consists of a pair of identical chromatids attached together by a structure called a centromere.

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