Download 1: Chromosomes 2: Mitosis

Chromosomes, Mitosis, Meiosis
1: Chromosomes
Cell Division
Cell Division is the process by which cells reproduce.
information in the cell is contained in genes genes code for proteins proteins carry
out cellular functions
Each body cell that results from cell division must have an exact copy of the DNA in the
original cell.
Chromosome Structure
DNA in a nondividing cell exists as chromatin.
Chromatin: DNA wrapped around histones
Histones: a special protein molecule that DNA wraps around during chromosome
formation
Nucleosome: the histone complex around which DNA wraps itself when coiling into
chromatin
Supercoiled chromatin forms chromosomes
Chromosome: DNA is a coiled, rod-shaped form that occurs during cell division
Chromatid: one of two identical parts of a chromosome
Centromere: the point at which each pair of chromatids is attached
Chromosome Numbers
Every species has a characteristic number of chromosomes in each cell.
Chromosome number is not an indication of the complexity of a species.
Homologous Chromosome: one of two members of a pair of morphologically similar
chromosomes
Each chromosome of a pair has the same size and shape as its homologue.
The pair is structurally different from all other homologous pairs in the cell.
Karyotype: a picture of an individual’s chromosomes
Diploid (2n): a cell that contains both chromosomes of a homologous pair
Humans = 46 (somatic cells: body cells)
Haploid (n): a cell that has only one chromosome of each homologous pair
Humans = 23 (gametes: egg and sperm)
2: Mitosis
Mitosis: the division of the cell nucleus in which the chromosomes in the parent cell divide into
two identical sets
In somatic cells (body cells), the number of cells is increased without changing the
information contained in the DNA or the amount of DNA in those cells.
Binary Fission: cellular division of unicellular organisms that produces identical offspring
Control of cell division = cell size (SA/V) and regulatory checkpoints
The Cell Cycle
Cell Cycle: the sequence of events that occurs in a cell from mitosis to mitosis
Interphase: a period of cell growth and development that precedes mitosis and follows
cytokinesis (largest part of the cell life cycle)
G1 Phase: cell doubles in size, enzymes and organelles double in number
o Cells that stop growing and dividing remain in G1 phase.
o Examples: muscle and nerve cells of animals
S Phase: DNA replication
G2 Phase: cell undergoes rapid growth that prepares it for mitosis, synthesizing
necessary enzymes and structures
Mitosis (PMAT)
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis: the division of the cytoplasm of a parent cell and its contents into two
daughter cells
Centriole: a rod-shaped structure that appears during mitosis and is responsible for
spindle formation and movement
Aster: a centriole with its radiating fibers that is active during cell division
Spindle Fiber: one of the microtubules of protein that develop during the middle period of
prophase in mitosis and that aid in chromosome movement
Polar Fiber: a type of spindle fiber that extends across the cell from centriole to
centriole
Kinetochore Fiber: a fiber extending from a centriole to a centromere during mitosis
3: Meiosis
Meiosis: the process of nuclear division that reduces the number of chromosomes in a cell by
half
Meiosis I: a division during meiosis in which the homologous chromosomes are
separated into separate cells
Meiosis II: a division during meiosis in which the chromatids are segregated into
separate cells
Tetrads: the grouping of two homologous chromosomes during meiosis (process =
synapsis)
Crossing-Over: the exchange of genes by homologous chromosomes during meiosis
Genetic Recombination: the process that results in chromosomes being arranged in many
different ways
crossing-over between homologues or chromatids
homologous pairs separate independently in meiosis I
sister chromatids separate independently in meiosis II
Formation of Egg and Sperm & Fertilization
Gamete: a sexual reproductive cell
Spermatogenesis: formation of sperm
Sperm: male gamete
Oogenesis: formation of eggs
Ootid: a cell that develops into an egg
Egg: female gamete
Polar Bodies: a cell formed during meiosis in females that receives little or no
cytoplasm and eventually disintegrates
Fertilization: the fusion of gametes
Zygote: the cell that results from the fusion of gametes