sex chromosomes

Both sex chromosomes are acrocentric, and X is larger than Y.

They may be caused by genes on either autosomal or sex chromosomes.

They have no sex chromosomes.

sets of chromosomes

Most multicellular organisms have two sets of chromosomes; that is, they are diploid.

the genome of a single individual (J. Craig Venter) in which both sets of chromosomes were sequenced.

Fertilized eggs get two sets of chromosomes, one from each parent, and so larva develop into diploid females, while unfertilized eggs only contain one set from the mother, so develop into haploid males or drones.

number of chromosomes   (染色体の数)

The number of chromosomes appears to be seven.

The number of chromosomes is unknown.

Low and manageable number of chromosomes make "Drosophila" species easier to study.