Why are chromosomes sorted into pairs of similar length?

Natalie had random hand movements when she was two months old. when she was six months old, she used to grab a block with her whole hand. now at the age of ten months, she can grasp the same block with her thumb and forefinger. this sequence of growth in her hand and finger movements is according to the pattern.

In which part of the body is a ball-and-socket joint found?

Which atmospheric later is where earths northern and southern lights occur