Why do egg cells contain only one X chromosome?

In which case would a scientist choose to use a dissecting microscope rather than a compound microscope

Dna. we have heard that we are a product of our dna. but where is it? how do we "get" our dna? it is passed to us, from our parents, but in what form? several vocabulary words associated with inheritance are used interchangeably and sometimes, incorrectly. let's see if you can clear this up for someone just learning about inheritance and cell structure.

Which of the following is the earliest era of earth's geologic time scale? cenozoic mesozoic precambrian paleozoic