Cell Division, Genetics, and Molecular Biology Review

Comprehensive vocabulary flashcards covering the cell cycle, mitosis, meiosis, gametogenesis, stem cell ethics, cancer biology, and chromosomal abnormalities.

Prokaryotes

Primitive organisms that lack a nucleus and membrane-bound organelles.

Eukaryotes

Advanced organisms characterized by a well-defined nucleus and membrane-bound organelles.

Chromatin

"Unpackaged DNA" that condenses into chromosomes only when a cell is about to divide; human cell nuclei contain approximately $3\,\text{meters}$ of it.

Alleles

Different versions of a gene located at the exact same location on each homologous chromosome.

Diploid ($2n$)

A cell or organism possessing paired chromosomes (one from each parent); in human somatic cells, $2n = 46$.

Haploid ($n$)

The quality of a cell or organism possessing a single set of chromosomes; in human gametes, $n = 23$.

Polyploid organisms

Organisms whose cells contain more than two homologous chromosomes per set (such as $3n = 54$).

$G_1$ Phase (1st Gap)

The subphase of interphase where the cell undergoes growth and performs its everyday cellular duties.

$S$ Phase (DNA Synthesis)

The subphase of interphase dedicated to copying chromosomes through DNA replication.

$G_2$ Phase (2nd Gap)

The final preparation phase of interphase before division, where the cell grows, stores energy, and synthesizes organelles, proteins, and membranes.

Mitosis

Cell division performed by autosomes for growth, maintenance, and repair, generating two daughter cells genetically identical to the parent cell.

Metaphase plate

The plane along the cell's equator where duplicated chromosomes align in single file during metaphase.

Homologous chromosomes (Homologues)

Pairs of chromosomes that share the same gene sequence, length, centromere location, and banding pattern, with one derived from maternal origin and one from paternal origin.

Cleavage furrow

A constriction belt of actin microfilaments around the cell equator in animal cells that contracts like a drawstring to pinch the cell into two during cytokinesis.

Cell plate

A dividing structure that forms between daughter nuclei in plant cells during cytokinesis, overcoming the rigid cell wall to eventually develop into a new cell wall.

Mutagens

Physical, chemical, or biological agents capable of altering an organism's genetic material and potentially leading to uncontrolled cell division.

Carcinogens

A specific class of mutagens that directly lead to the formation of cancerous cells.

Oncogenes

Genes that stimulate the cell cycle and promote cell growth.

Tumour suppressor genes

Genes that act to repress cell division and trigger apoptosis (programmed cell death).

Metastasis

The dissemination of cancer from a primary tumour to distant sites via the bloodstream or vessels, establishing a secondary tumour.

Identical (monozygotic) twins

Twins formed when a single fertilized egg splits in two during development, resulting in individuals with identical DNA.

Fraternal (dizygotic) twins

Twins developed when two independent eggs are fertilized simultaneously by different sperm cells, resulting in non-identical DNA.

Totipotent

The developmental potential to differentiate into any cell type, a quality exclusively held by the zygote, making embryonic harvesting ethically contentious.

Pluripotent stem cells

Stem cells that can easily be harvested from adult tissues and utilized to clone individual cells, tissues, or organs.

Telomeres

Protective caps at the ends of chromosomes that shorten after each round of cell division, functioning as a "molecular clock" for aging; their failure to shorten is indicative of cancerous cells.

Synapsis

The pairing and physical alignment of homologous chromosomes during Prophase 1 of meiosis.

Crossing over

The exchange or "mixing of genes" between homologous chromosomes that takes place exclusively during Prophase 1 of meiosis.

Independent assortment

The random, independent alignment of homologous chromosome pairs along the equatorial plate during Metaphase 1.

Nondisjunction

The failure of homologous chromosome pairs or sister chromatids to separate properly during Meiosis 1 or Meiosis 2, resulting in gametes with abnormal chromosome numbers.

Aneuploidy

An abnormal chromosomal condition upon fertilization characterized by having one chromosome less (monosomy) or one chromosome more (trisomy).

Turner syndrome

A monosomic condition caused by nondisjunction in which an individual has one X chromosome and no second sex chromosome.

Trisomy 21

An aneuploid condition characterized by three copies of chromosome 21 ($OO + O = OOO$), often correlated with centromeres becoming "sticky" as maternal age increases.

Spermatogenesis

The male gamete production pathway wherein a diploid germ cell undergoes mitosis and two meiotic divisions to yield four functional haploid spermatids that mature into sperm.

Oogenesis

The female gamete production pathway involving unequal cytoplasmic division, yielding a single viable haploid ovum alongside nonfunctional polar bodies.

Polar bodies

Small, nonviable haploid cells formed during oogenesis that receive minimal cytoplasm and degenerate, leaving one mature ovum.