1. Chromosome Review
Chromosomes—those strands of DNA and protein inside the cell nucleus—are the carriers of genes. The genes are located in specific positions on chromosomes.
The term Diploid describes an organisms that has two complete SETS of chromosomes one from each parent.
This means for each gene there are two ALLELES
Alleles are variations of the same gene.

2. Diploid Cells
A body cell in an adult fruit fly has eight chromosomes, as shown in the figure.
Four of the chromosomes come from its male parent, and four come from its female parent.
These two sets of chromosomes are homologous.
Homologous chromosomes each carry the same genes in the same order, but the alleles for each trait may not be the same.

3. Haploid Cells
Haploid cells contain only a single set of chromosomes, and therefore a single set of genes.
The gametes (egg or sperm) of sexually reproducing organisms are haploid.

4. Phases of Meiosis
Meiosis is a process in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell.
Human diploid cells in the ovaries or testies undergo meiosis to produce mature eggs and sperm