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During cell division, the DNA in eukaryotic cell's nucleus is coiled into very compact structures called _____________.


The DNA in eukaryotic cells wraps tightly around proteins called _____________.


____________ proteins are generally involved in controlling the activity of specific regions of the DNA.


Each half of the chromosome.


The constricted area of each chromatid.

sex chromosomes

Chromosomes that determine the sex of an organism, and they may also carry genes for another characteristic


Chromosomes that do not determine the sex of an organism.


Number of human autosomes.


Number of human sex chromosomes

homologous chromosomes

The two copies of each autosome organisms receive from their parents.


Photomicrograph of the chromosomes in a dividing cell found in a normal human.


Cells having two sets of chromosomes.


Human sperm cells and egg cells (they contain only one set of chromosomes).

binary fission

The division of a prokaryotic cell into two offspring cells.


Cell division in eukaryotes that results in new cells with genetic material that is identical to that of the original cell.


Cell division in eukaryotes in which the chromosome number is reduced by half in new cells.

cell cycle

The repeating set of events that make up the life of a cell.


The time between cell division. It is divided into 3 phases.


Phase of cell division. During this phase, the nucleus of a cell divides. It can also be called the M phase.


Phase of cell division. During this phase, the cytoplasm of the cell divides.

G1 phase

Phase of interphase. During this phase, the cell grows, creates organelles and begins metabolism.

S phase

Phase of interphase. During this phase occurs DNA synthesis and the duplication of the centrosome.

G2 phase

Phase of interphase. During this phase, the cell grows in preparation for cell division.

G0 phase

Phase of interphase. During this phase, the cells exit the cell cycle and are alive and metabolically active, but do not divide. They don't copy their DNA and don't prepare for cell division. If they are damaged, they cannot be replaced. This does not always occur, but if it does, it's usually from G1 phase.

heart muscle, eyes, and brain

Some examples of cells that enter G0 phase.

somatic cells

body cells

germ cells

cells destined to become sperm in males or ova (eggs) in females


genetic material in interphase. It cannot be clearly seen because it is not tightly coiled.


First phase of mitosis. During this phase, the DNA molecules are shortened and condensed by coiling. Spindle fibers are formed during this phase.

nuclear membrane and nucleolus

Enzymes during prophase break down the_______________________ so they are no longer visible.


Second phase of mitosis. During this phase, the spindle fibers attach themselves to the centromeres of the chromosomes and align the chromosomes at the equator.


middle of the cell


Third phase of mitosis. During this phase, the spindle fibers shorten and the centromere splits separating the two sister chromatids.


Fourth phase of mitosis. During this phase, the chromosome pairs are pulled to opposite poles of the cell. The nuclear envelope and nucleolus reform before the chromosomes uncoil. The spindle fibers disintegrate.


chromosome pair.


reproductive cells

meiosis I

The stages of the first cell division in meiosis.

meiosis II

The stages of the second cell division in meiosis.


The pairing of homologous chromosomes, which does not occur in mitosis. It occurs in prophase I in meiosis.


Each pair of homologous chromosomes.


During synapsis, the chromatids with a homologous pair twist around one another. Portions of chromatids may break off and attach to adjacent chromatids on the homologous chromosome. This process is called ___________________. It permits the exchange of genetic material between maternal and paternal chromosomes.

genetic recombination

A new mixture of genetic material.

independent assortment

The random separation of the homologous chromosomes.

meiosis II

Process that occurs in each cell formed during meiosis I an is NOT preceded by the copying of DNA.


haploid reproductive cells.


In the development of sperm cells, a diploid reproductive cell divide meiotically to form four haploid cells called __________________.


The production of sperm cells.


The production of mature egg cells.

polar bodies

During cytokinesis I and cytokinesis II of oogenesis, the cytoplasm of the original cell is divided unequally between new cells. One cell, which develops into a mature egg cell, receives most of the cytoplasm of the original cell. As a result, one egg cell is produced by meiosis. The other three products of meiosis, called ____________, degenerate.

asexual reproduction

The production of offspring from one parent.

sexual reproduction

The production of offspring through meiosis an the union of a sperm and an egg.

cleavage furrow

During mitosis, animal cells divide the cytoplasm by constricting the cell membrane in the middle to form a _________.

cell plate

Plant cells form a ______________ in the center to divide the cytoplasm.



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