The movement of chromosomes towards the poles by the mitotic spindle during mitosis.
Anaphase I
During meiosis I, when homologous chromosomes are pulled towards the poles by the meiotic spindle. Sister chromatids remain attached to each other: they don't separate at this stage.
Aneuploidy
The condition that describes when a cell has lost or gained a copy of a particular chromosome.
Cell Cycle
The process by which the cell goes from one cell division event to the next. It can be broken down into two general stages by light microscopy, called interphase and M phase. Interphase can be further divided into G1, S, and G2 phases. These steps include all of the necessary preparations that a cell must make to generate two genetically identical daughter cells.
Centromere
The centermost region of a chromosome where sister chromatids are tightly attached to each other, and where the mitotic spindle attaches to each chromatid.
Centrosome
The microtubule organizing center of the mitotic spindle. Sometimes also known as a centriole.
Chiasmata (singular Chiasma)
Structures generated by recombination of homologous chromosomes during meiosis I, which are also important for holding the homologous chromosomes together. Means "cross-shaped."
Chromatid
The identical copies of a chromosome's DNA molecule formed by DNA replication. The two copies are called sister chromatids, and they are held together at the centromere until it is time for them to separate during cell division.
Chromosome
A structure that contains the DNA of an organism and the proteins (known as histones) that are important for making up that structure. For most of the cell cycle, each chromosome consists of one complete DNA molecule that is then copied during the S phase. During cell division, the chromosome takes on a compact structure, through a process called condensation. Uncondensed chromosomes are usually referred to all together as chromatin, or the dark staining material visible in the nucleus during interphase.
Cytokinesis
A part of M phase of the cell cycle, cytokinesis refers to the process by which the entire cell is divided in two
Diploid
Having two of each chromosome, one from each parent. This is in contrast to a haploid cell, which only has one copy of every chromosome.
G0 Phase
The "resting" phase where cells that have temporarily (or permanently) exited the cell cycle reside. This phase is also referred to as quiescence.
G1 Phase
Gap 1 phase, the "growing" phase where the cell replicates its organelles and produces all the proteins needed for replication and mitosis.
G2 Phase
Gap 2 phase, the phase between S phase and M phase, when the cell continues to grow and produce the proteins needed for cell division.
Haploid
Having only one of each chromosome, such as an egg (oocyte) or sperm.
Homologous Chromosome
One of the two copies of a chromosome contained in a diploid cell, with each copy coming from one parent.
Interphase
The G1, S, and G2 phases of the cell cycle, where a cell grows, replicates its DNA and prepares for mitosis.
M Phase
The actual division phase of the cell cycle, where the identical chromatids generated by replication are physically separated into two separate cells. This step therefore includes both the nuclear segregation of the chromosomes (called mitosis) and cytokinesis, where the cell divides into two identical daughter cells.
Metaphase
The stage of mitosis where all the chromosomes are aligned in a straight line down the center of the cell, with each sister chromatid attached to the mitotic spindle emanating from one of the poles of the cell.
Metaphase I
During meiosis I, where the homologous chromosomes align in the center of the cell.
Meiosis
A special cell division process where the number of chromosomes in a parent cell is reduced by half, such that each daughter cell contains only one member of a pair of homologous chromosomes. Meiosis occurs in two successive division stages, meiosis I and meiosis II.
Meiosis I
The first division stage of meiosis where homologous chromosomes separate, resulting in the production of 2 haploid cells containing half the number of chromosomes of a diploid cell. Can be thought of as a "reduction division."
Meoisis II
The second division stage of meiosis where sister chromatids segregate, resulting in the production of four genetically different haploid cells and the completion of meiosis. A lot like mitosis, only with half the number of chromosomes.
Mitosis
A part of M phase of the cell cycle, mitosis refers to nuclear division, where the replicated sister chromatids are pulled apart and segregated into two genetically identical nuclei.
Mitotic Spindle
A group of microtubules that form between opposite poles of a cell at the centrosomes and pull the duplicated (sister) chromatids apart during mitosis.
Prometaphase
The stage of mitosis where the chromosomes begin to attach to the mitotic spindle and begin to align along the center (equator) of the cell.
Prophase
The initial stage of mitosis where the nuclear envelope begins to break down, the cell's chromatin condenses into rod-shaped chromosomes and the mitotic spindle begins to assemble.
Prophase I
The first stage of meiosis I, where the nuclear envelope breaks down, homologous chromosomes pair and genetic recombination is induced.
Recombination
The process by which DNA strands are broken and repaired using unbroken DNA molecules as templates. In meiosis, recombination is induced between the homologous chromosomes that results in the reshuffling of genetic material.
S Phase
Synthesis phase, the phase of the cell cycle where the DNA in the cell is replicated, resulting in the production of two identical sister chromatids for each chromosome.
Synaptonemal Complex
A special structure that promotes pairing of homologous chromosomes in meiosis and recombination between these homologous chromosomes.
Telophase
The final stage of mitosis where the sister chromatids decondense to their more interphase-like structures and the nuclear envelope reforms.