Cell Cycle

Differences between cell division in plants and animals...

1. Plants cells lack centrioles. The spindle apparatus is organized by micro tubule organizing centers which are not visible. 2. Plant cells are rigid and cannot form a cleavage furrow. So instead they form and expanding partition that grows outward from the interior of the cell until it reaches the cell membrane.

Prophase

Chromosomes condense, in animal cells centrioles pair separate and move towards the opposite poles of the cell. The spindle apparatus forms between them and nuclear membrane dissolves which allows the spindle fibers to interact with the chromosomes.

Karyokinesis

Division of nuclear material

Cytokinesis

Occurs near the end of telophase. The cytoplasm divides into two daughter cells with a complete nucleus and it's own set of organelles. In animal cells a cleavage furrow forms and the cell Membrane indents along the equator of the cell and firmly pinches through the cell which separates the two cells.

Meiosis

Process by which sex cells are produced. Half's the chromosomes forming the haploid number. Involves two divisions of primary sex cells forming four haploid cells called gametes. occurs in sex cells only.

First meiotic division

Produces two intermediate daughter cells with N chromosomes with sister chromatids

Metaphase

The centriole pairs are now at opposite poles of the cell. The fibers of the spindle apparatus attaches to each chromatid at the centromere to align the chromosomes at the center of the cell ( equator) forming the metaphase plate

Anaphase

The centromeres split so that each chromosome has it's own distinct centromere which allows the sister chromatids to separate. The two separated sister chromatids are now considered as two separate chromosomes. The sister chromatids are pulled at the opposite ends of the poles by the shortening of the spindle fibers which are made up of microtubules.

Interphase

The phase where cell spends 90% of it life cycle. In this phase genetic material is replicated and a second sister chromatid is made. Both sister chromatids are considered as one chromosome

Telophase

The spindle apparatus disappears, a nuclear membrane forms around each newly set of chromosomes. Thus each. Ulcers contains the same number of chromosomes. The chromosomes uncoil and remain into their interphase chromatin form.

Chromatin

Uncondensed form of DNA. Exists during interphase part of cell cycle and is not visible. Chromatin condenses into chromosomes during cellular replication

Telophase

a nuclear membrane forms around each new nucleus. at this point chromosomes still consist of sister chromatids joined together at the centromere.

Prophase 1

chromatin condenses into chromosomes, the spindle apparatus forms and the nuclear membrane and the nucleoli disappear. homologous chromosomes come together and intertwine in a process called synapsis.

Tetrad

formed during prophase 1 when four homologous chromatids are paired together.

metaphase 1

homologous pairs align at the equatorial plane and each pair attaches to a separate spindle fibre by its kinetochore.

Mitosis

occurs in all dividing cells. homologous chromosomes don't pair up. no crossing over occurs.

second meiotic devision

similar to mitosis except that it is not preceded by chromosomal replication. the chromosomes align at the equator, separate and move to opposite poles and are surrounded by a re-formed nuclear membrane. the new cells have the haploid number of chromosomes. in human females only one of these daughter cell becomes a functional gamete.

Anaphase 1

the homologous pairs separate and are pulled to opposite poles of the cell. this process is called disjunction and it is a random process that will give rise to each daughter cell having a unique pool of genes.

crossing over

when chromatids of homologous chromosomes break at corresponding points and exchange equivalent pieces of DNA. note: crossing over occurs between homologous chromosomes and between the chromatids of the same chromosomes. once recombination has occurred, the sister chromatids are no longer considered to be identical. this method allows for genetic .