Chromosomes
In a eukaryotic cell, a rod-shaped structure in a cell's nucleus that are made up of DNA and proteins; in a prokaryotic cell, the main ring of DNA
Histones
Proteins which help maintain the shape of the chromosomes and help in the tight packing of DNA
Chromatid
Half of a chromosome, identical to the other half
Centromere
The point at which a chromosome's two chromatids are connected
Chromatin
A complex of proteins and DNA strands that are loosely coiled so that translation and transcription can occur
Sex Chromosomes
Chromosomes that determine the sex of an organism, and they may also carry genes for other characteristics
Autosomes
All the chromosomes in an organism besides the sex chromosomes
Homologous Chromosomes
The two copies of each chromosome an organism recieves from each of its parents
Karyotype
A photomicrograph of the chromosomes in a normal dividing cell found in a human
Diploid
Describes cells that have two sets of chromosomes
Haploid
Describes cells that have one set of chromosomes
Binary Fission
The division of a prokaryotic cell into two offspring cells
Mitosis
A type of cell division that results in new cells with genetic material identical to that of the original cell
Asexual Reproduction
The production of offspring from one parent
Meiosis
A process in cell division in which the number of chromosomes decreases to half the original number by two divisions of the nucleus, which results in the production of sex cells
Interphase
The time between cell divisions, during which a cell grows to mature size, its DNA is copied, and it prepares for cell division
Cytokinesis
The division of a cell's cytoplasm
Prophase
The first stage of mitosis, where a cell's chromosomes condense, its nucleolus and nuclear membrane break down and disappear, centrosomes move to opposite ends of the cell, and spindle fibers radiate from them in preperation for metaphase
Metaphase
The second phase of mitosis, where a cell's chromosomes move toward its center and are held in place by the spindle fibers
Anaphase
The third phase of mitosis, where the chromatids of each of a cell's chromosomes seperate at the center of the cell and move toward opposite ends of the cell
Telophase
The final phase of mitosis where a cell's chromosomes reach opposite ends of the cell, its spindle fibers dissasemble, chromosomes turn back into chromatin (less tightly coiled chromosomes) and a nuclear envelope forms around each of the chromosome sets,
Cell Plate
Formed during plant cell division; eventually the cell wall forms from it, dividing the cell into two
Cell Growth (G1) Checkpoint
Proteins at this checkpoint control whether the cell will divide; if the cell is healthy and has grown to a suitable size, the proteins will initiate the S phase
DNA Synthesis (G2) Checkpoint
DNA repair enzymes check the results of DNA replication, and if the checkpoint is passed, proteins will signal the cell to begin molecular processes that will allow the cell to divide mitotically
Mitosis Checkpoint
If a cell passes this checkpoint, proteins will signal for the cell to exit mitosis, and it will then enter into the G1 phase again
Synapsis
The pairing of homologous chromosomes which occurs only in meiosis
Tetrad
A pair of homologous chromosomes
Crossing-over
A process in which portions of chromatids may break off and attach to adjecent chromatids on its homologous chromosome pair
Genetic Recombination
The regrouping of genes in an offspring that results in a genetic makeup that is different from that of the parents
Independant Assortment
The random seperation of homologous chromosomes during anaphase I of meiosis
Spermatogenesis
The production of sperm cells
Oogenesis
The production of mature egg cells
Sexual Reproduction
The production of offspring through meiosis and the union of a sperm and an egg