Term | Definition |
cell cycle | life cycle of the cell; G1, S. G2 (DNA replication occurs in the S phase) |
allele | an alternate form of a gene |
crossing over | An exchange of genetic material between homologous chromosomes during anaphase I of meiosis; contributes to the genetic variability in gametes and ultimately in offspring |
gamete | A specialized cell (egg or sperm) used in sexual reproduction containing half the normal number of chromosomes of a somatic cell |
meiosis | A two‐phase nuclear division that results in the eventual production of gametes with half the normal number of chromosomes |
mitosis | A nuclear division resulting in the production of two somatic cells having the same genetic complement as the original cell |
DNA replication | The process in which DNA makes a duplicate copy of itself |
chromosome | A thread-like, gene carrying structure found in the nucleus; Each chromosome consists of one very long DNA molecule and associated proteins |
cytokinesis | final phase of the cell cycle during which the cytoplasm divides in two |
prophase | nuclear membrane breaks down; DNA molecules coil up, making chromosomes condense |
metaphase | centrioles produce spindles which attach to the centromeres; chromatids line up along the middle |
anaphase | spindle fibers pull chromatids away from the center to opposites poles of the cell |
telophase | new nuclear membranes form around the newly separated chromosomes |
propphase I | nuclear membrane breaks down; homologous chromosomes pair up; crossing over occurs |
metaphase I | spindles attach to the centromeres of the sister chromatids; sister chromatids line up along the middle of the cell |
anaphase I | pairs of homologous chromosomes are pulled away to opposite poles of the cell (sister chromatids remain attached, unlike mitosis) |
telophase I | two cells form |
prophase II | chromosomes condense again; new spindles form |
metaphase II | spindles attach to centromeres of the sister chromatids; chromatids line up along the middle of the cell |
anaphase II | sister chromatids are pulled away from the center to opposite poles of the cell |
telophase II | nuclear membranes form; now have 4 genetically different, haploid (half the number of chromosomes) cells |
haploid | half the number of chromosomes |
diploid | full set of chromosomes |