Mitosis and Meiosis

Practice flashcards covering the definitions, phases, and biological importance of mitosis and meiosis based on Year 9 Science lecture notes.

Cell Proliferation

The process in multicellular organisms by which a cell grows and divides to produce two daughter cells, occurring for organism growth, replacement of dead cells, and tissue repair.

Mitosis

A single nuclear division that results in two genetically identical nuclei.

DNA Replication

The process that occurs before mitosis where DNA is duplicated so that each daughter cell will have its own nucleus and not be "missing" DNA.

Chromosomes

Structures formed when long strands of DNA package themselves; they replicate to form two chromatids attached at the centre.

Centrioles

Organelles from which spindles form during the prophase stage of cell division.

Spindles

Organelles that act like the skeleton of the cell with a function to move things around during mitosis.

Cancer

Unregulated cell growth or division that results when mitosis proceeds when it should not, which can form tumours and impede organ function.

Sexual Reproduction

Reproduction involving two parents and the fusion of gametes ($\text{egg}$ or $\text{sperm}$), producing genetically unique offspring to increase genetic variation.

Gametes

Cells formed in meiosis that contain a nucleus with half the amount of DNA; include spermatozoa ($\text{sperm}$) and oocytes ($\text{egg}$).

Meiosis

A type of nuclear division involving two rounds of division that produces four genetically diverse daughter cells with half as many chromosomes as the parent cell.

Homologous Chromosomes

A pair of chromosomes found in eukaryotic cells, with one inherited from the mother and one from the father.

Diploid ($2n$)

Cells or organisms containing a homologous pair of each chromosome; in humans, $2n = 46$.

Chromosome Number

The total number of chromosomes in a typical body cell with all sets combined.

Ploidy Number

The number of sets of chromosomes, such as the two in diploid ($2n$) indicating one maternal and one paternal set.

Haploid ($n$)

A cell or organism with a single copy of each chromosome ($n = 23$ in humans), such as eggs and sperm.

Synapsis

The tight pairing of homologous chromosomes during Prophase I where genes on the chromatids are aligned with each other.

Crossing Over

The process where homologous chromosomes swap pieces of DNA during Prophase I to increase genetic variation.

Independent Assortment

The random orientation of each homologous pair at the cell equator during Metaphase I, which increases genetic variation.

Prophase (Mitosis)

The phase where replicated DNA in chromatin form condenses into chromosomes, the nuclear membrane breaks apart, and spindles form from centrioles.

Metaphase (Mitosis)

The phase where spindles attach to the centre of each chromosome and move them to align in the centre of the cell.

Anaphase (Mitosis)

The phase where spindles pull the chromatids apart to separate the duplicated chromosome and move them towards the poles of the cell.

Telophase (Mitosis)

The phase where the nuclear membrane reforms around each set of daughter chromosomes, chromosomes decondense into chromatin, and spindles break down.

Prophase I (Meiosis)

The phase where homologous chromosomes pair up (synapsis) and crossing over occurs, allowing for genetic variation.

Metaphase I (Meiosis)

The phase where paired homologous chromosomes align at the cell equator, with spindle fibres attached.

Anaphase I (Meiosis)

The phase where spindle fibres separate homologous chromosome pairs towards opposite poles, while sister chromatids remain attached.

Telophase I (Meiosis)

The phase where two haploid nuclei form, and the cell divides into two cells.

Prophase II (Meiosis)

The phase where the chromosomes condense again and spindle fibers form in the two haploid cells.

Metaphase II (Meiosis)

The phase where chromosomes line up individually along the cell equator in each haploid cell.

Anaphase II (Meiosis)

The phase where sister chromatids are pulled apart and move towards opposite poles of the cell by spindle fibres.

Telophase II (Meiosis)

The final stage of meiosis resulting in four haploid ($n$) daughter cells where DNA uncoils and is no longer $X$-shaped.