Cell Division

Synthesis (S)

DNA replicates

Metaphase I

Second stage of Meiosis I. Tetrads line up (homologous chromosomes stay together) at the equatorial plate

Gap 2 (G2)

cell prepares for mitosis

Interkinesis

interphase-like stage but NO DNA replication (very brief)

Tumors (cancers)

the result of uncontrolled cell division and can occur in any organ or tissue.

Mitosis

A process that involves the nucleus and ensures that each new nucleus receives the same number and types of chromosomes present in the original nucleus.; used for the growth and repair of stomatic cells; each new cell receives an identical copy of the DNA from the mother cell; usually immediately followed by cytokinesis; 4 phases

Outline interphase stage of the cell cycle

An active period in the life of a cell when many metabolic reactions occur, including protein synthesis, DNA replication, and an increase in the number of mitochondria and/or chloroplasts - the period of time when the cell is NOT dividing. Most of the cell's life is spent in this stage. It is composed of the 3 stages (G1, S, G2).

Explain how mitosis produces two genetically identical nuclei.

During prophase, the chromosomes become visible under a light microscope as they super coil. The nuclear envelope disintegrates and the spindle microtubules grow and extend from each pole to the equator. At metaphase the chromatids move to the equator. The sister chromatids are two DNA molecules formed by DNA replication and are therefore identical. These sister chromatids are then separated in anaphase as the spindle microtubules attaches to centromere and pulls the sister chromatids to opposite poles. As the sister chromatids separate they are called chromosomes. This means that each pole has the same chromosomes (same genetic material). Finally the microtubules break down, the chromosomes uncoil and the nuclear membrane reforms. The cell then divides into two daughter cells with genetically identical nuclei.

Prophase I

First stage of Meiosis I. Same events as mitosis with the following exceptions: homologous chromosomes come together with their partners (process is called synapsis). Crossing over occurs (the exchange of genetic material between non-sister chromatids during prophase I)

Telophase I

Fourth and final stage of Meiosis I. Nuclear membrane may reorganize, chromosomes decondense somewhat; each cell is now haploid but still contains two copies

Telophase

Fourth and last stage of mitosis; nuclear membrane and nucleoli reappear, chromosomes return to chromatin, cytokinesis begins

Metaphase

Second stage of mitosis; chromosomes line up at the equatorial plate (single file)

Anaphase I

Third stage of Meiosis I. Homologous partners separate & sister chromatids STAY TOGETHER (centromere does not split) and move together to opposite poles

Anaphase

Third stage of mitosis; sister chromatids are pulled apart to opposite poles

Meiosis

a reduction division of a diploid nucleus to form haploid nuclei.

Non-disjunction

can lead to changes in chromosomes number. This is when the chromosomes do not separate properly during meiosis, either in meiosis I (in anaphase I) or meiosis II (in anaphase II). This leads the production of gametes that either have a chromosome too many or too few. Down syndrome (trisomy 21) is a disease in which the chromosomes failed to separate properly during meiosis leading to three chromosomes of type 21 instead of two.

Gap 1 (G1)

cell grows in size; organelles are duplicated

Meiosis I

chromosomes duplicate during interphase prior to meiosis I

Homologous chromosomes

chromosomes with the same genes as each other, in the same sequence but do not necessarily have the same allele of those genes.

Meiosis II

consists of prophase II, metaphase II, anaphase II, and telophase II; events essentially the same as mitosis except it results in four haploid daughter cells.

Cytokineses

division of the cytoplasm to form 2 daughter cells; division of animal cells begins with a ring of actin microfillaments forming a cleavage furrow; division of plant cells occurs through formation of a cell plate

Prophase

first stage of mitosis; chromosomes coil and condense and become visible. Centrioles duplicate and migrate to opposite poles, mitotic spindle forms, asters form. In animal cells, mitotic spindle grows from centrioles. Chromosomes attach to spindle fibers at the kinetochore. Nuclear membrane breaks down and disappears; nucleoli disappears.

State four processes that involve mitosis.

growth, embryonic development, tissue repair, and asexual reproduction.

Outline the process of Meiosis

it is divided into 2 cell divisions. See slides Meiosis I, Prophase I, Metaphase I, Anaphase I, Telophase I, Interkineses, Meiosis II.

Describe the events that occur in the four phases of mitosis (prophase, metaphase, anaphase, and telophase)

supercoiling of chromosomes, attachment of spindle microtubules to centromeres, splitting of centromeres, movement of sister chromosomes to opposite poles, and breakage and re-formation of nuclear membranes