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haploid
. 
 
Figure 30. 
A female human somatic cell contains 23 pairs of homologous chromosomes. These 
chromosomes are shown in the nucleus (top), shed from a cell during mitosis (right), and arranged in a 
pattern known as a karyotype (left). To distinguish the chromosomes, they were exposed to fluorescent 
stains
17
. 
 
Homologous chromosomes
are the matching pairs of chromosomes found in diploid organisms. The 
length of homologous chromosomes is the same, and they share a locus with other chromosomes that contain 
the same set of genes.
18
. 
2.4 Reading Resource #2: 
The Cell Cycle 
The cell cycle is an organized sequence of cell growth and division events that results in the creation 
of two new daughter cells. To produce two genetically identical cells, cells go through a series of carefully 
timed and regulated stages of growth, DNA replication, and division. The cell cycle has two major phases: 
interphase
and the 
mitotic phase
(Figure 31). DNA replication and cell growth occur during interphase. The 
17
“718 Bot”/Wikimedia Commons, National Human Genome Research
18
Fowler, S., Roush, R. & Wise, J. (2017) 
Concepts in Biology, 
Chapter 6, -Pp. 135-138. OpenStax, 
https://openstax.org/details/books/concepts-biology
 

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cell divides and the replicated DNA and cytoplasm are separated during the mitotic phase. Watch this video to 
learn more about the cell cycle
1920
 
Figure 31.
A cell undergoes a sequence of phases in an organized way. During interphase, 
G1
involves cell 
growth and protein synthesis, the 
S phase
involves DNA replication and the replication of the centrosome, 
and 
G2
involves further growth and protein synthesis. The interphase is followed by the mitotic phase. 
Nuclear division occurs during mitosis, a process in which duplicated chromosomes are separated and 
distributed among daughter nuclei. After mitosis, a process known as cytokinesis, in which the cytoplasm is 
divided and two daughter cells are created, usually occurs, the cell will divide. 
Interphase 
The cell prepares for cell division during interphase while also going through normal processes. 
Numerous internal and external requirements must be satisfied for a cell to transition from the interphase to the 
mitotic phase. The three interphase phases are designated as G1, S, and G2.