SBI3U1 Biology: Cell Division, Mitosis, Meiosis, and Heredity

Vocabulary practice flashcards covering cell division, mitosis, the stages of meiosis, spermatogenesis, oogenesis, chromosomal terminology, and heredity for SBI3U1 Biology.

Asexual Reproduction

A reproductive process involving only one parent where cells divide without the fusion of sex cells, producing offspring that are direct, invariable, and genetically identical to the parent and to each other.

Sexual Reproduction

A reproductive process usually involving two parents where two haploid sex cells fuse, producing genetically variable offspring that inherit half of their genetic information from each parent.

Heredity

The transmission and passing of genetic traits and characteristics from parents to offspring across generations.

Gene

A specific segment of DNA located at a particular locus on a chromosome that carries the instructions or genetic code for a specific trait.

Locus

The specific physical location or band of a gene on a chromosome.

Genome

The complete set of all genetic material and instructions contained within an organism.

Chromatin

The loose, unwound, thread-like form of DNA and associated proteins found within the nucleus during interphase when the cell is not dividing.

Chromosome

A highly organized and condensed structure of DNA and proteins visible during cell division that carries genetic information in the form of genes.

Chromosome Anatomy

The structural organization of a single chromatid chromosome, featuring protective end caps called telomeres, a short arm, a constricted centromere, and a long arm.

Dyad (Double Chromosome)

A duplicated chromosome consisting of two identical sister chromatids joined together at a centromere following DNA replication.

Sister Chromatids

Two identical copies of a replicated chromosome produced during the $S$ phase of interphase, joined together at a central centromere.

Centromere

The constricted chromosomal region that physically joins sister chromatids together and serves as the attachment site for spindle fibres during cell division.

Diploid ($2n$)

A cell that possesses two complete sets of homologous chromosomes, one set inherited from each parent ($46$ chromosomes arranged in $23$ pairs in humans).

Haploid ($n$)

A cell containing a single set of unpaired chromosomes, representing half the normal somatic complement ($23$ chromosomes in humans).

Polyploid

A cell or organism containing more than two complete homologous sets of chromosomes.

Cell Cycle

The continuous, orderly sequence of cellular growth and division consisting of interphase ($G_1$, $S$, $G_2$), mitosis, and cytokinesis.

$G_1$ Phase (Growth 1)

The first phase of interphase during which the cell increases in size, produces RNA and proteins, and prepares for DNA replication.

$S$ Phase (Synthesis)

The phase of interphase where DNA replication occurs, synthesizing a duplicate copy of each chromosome so that each consists of two sister chromatids.

$G_2$ Phase (Growth 2)

The final stage of interphase in which the cell continues growing, synthesizes additional proteins and organelles, and completes preparations for mitosis.

$G_0$ Phase

A non-dividing resting state outside the active cell cycle where cells pause division temporarily or permanently while continuing specialized metabolic functions.

Mitosis

A type of somatic cell division that divides the nucleus and separates duplicated chromosomes into two identical groups to facilitate growth, tissue repair, and cell replacement.

Prophase (Mitosis)

The first phase of mitosis where chromatin condenses into visible chromosomes, centrioles migrate to opposite poles, spindle fibres begin to form, and the nucleolus and nuclear membrane break down.

Metaphase (Mitosis)

The stage of mitosis in which chromosomes line up along the middle of the cell (equatorial plate) and spindle fibres attach to kinetochores at the centromeres.

Anaphase (Mitosis)

The mitotic phase where centromeres separate, sister chromatids are pulled apart as individual chromosomes, and spindle fibres shorten toward opposite cell poles.

Telophase (Mitosis)

The final phase of mitosis where chromosomes arrive at opposite poles, uncoil into chromatin, spindle fibres disassemble, and two new nuclear membranes form.

Cytokinesis

The physical division of the cytoplasm and cellular organelles following nuclear division, forming two daughter cells via a cleavage furrow in animal cells or a cell plate in plant cells.

Centrioles

Paired cylindrical organelles in animal cells that migrate to opposite poles during prophase to organize the spindle apparatus.

Spindle Fibres

Microtubule structures that extend from centrioles to attach to kinetochores, orchestrating the alignment and movement of chromosomes during division.

Meiosis

A specialized reduction division (derived from the Greek word meaning 'to diminish') occurring in gonads that halves chromosome count to generate four genetically variable haploid gametes.

Gametes

Haploid reproductive sex cells (ova/eggs in females and spermatozoa/sperm in males) that fuse during fertilization to establish a diploid zygote.

Somatic Cells

Any biological cells forming the body of an organism other than gametes or germ cells, possessing a diploid ($2n = 46$ in humans) chromosome count.

Synapsis

The precise pairing and close association of maternal and paternal homologous chromosomes during prophase I of meiosis to form tetrads.

Tetrad

A four-chromatid structure formed during prophase I by the physical alignment and synapsis of two homologous chromosomes.

Chiasma

The microscopic X-shaped intersection where non-sister chromatids of homologous chromosomes touch and exchange genetic segments during crossing over in prophase I.

Crossing Over (Recombination)

The reciprocal exchange of corresponding DNA segments between non-sister chromatids of homologous chromosomes during prophase I, yielding genetically distinct recombinant chromosomes.

Metaphase I

The meiotic stage where homologous chromosome pairs (tetrads) align randomly in two columns along the equatorial plate of the cell.

Anaphase I

The meiotic stage in which homologous chromosome pairs separate and move toward opposite poles, while sister chromatids remain attached at their centromeres.

Telophase I and Cytokinesis I

The conclusion of meiosis I where nuclear envelopes reform and the cell divides into two haploid daughter cells, each containing chromosomes composed of two sister chromatids.

Prophase II

The first phase of meiosis II where chromosomes condense and new spindle fibres assemble in each haploid cell without any prior DNA replication.

Metaphase II

The phase of meiosis II where duplicated chromosomes line up individually along the equatorial metaphase plate in each haploid cell.

Anaphase II

The meiotic phase where centromeres divide and sister chromatids separate, migrating toward opposite poles as individual single-chromatid chromosomes.

Telophase II and Cytokinesis II

The final stage of meiosis producing four genetically unique haploid ($n$) daughter cells, each possessing one single chromatid per chromosome pair.

Reduction Division

The specific designation for meiosis I because it reduces the overall chromosome number per cell by half (e.g., from $2n = 46$ down to $n = 23$ in humans).

Independent Assortment

The random orientation and segregation of maternal and paternal homologous chromosome pairs during metaphase I, producing $2^n$ possible gamete combinations ($2^{23} = 8{,}388{,}608$ in humans).

Non-disjunction

The abnormal failure of homologous chromosomes to separate during anaphase I or sister chromatids to separate during anaphase II, leading to aneuploid gametes with extra or missing chromosomes.

Trisomy

An aneuploid chromosomal condition wherein a zygote possesses three copies of a specific chromosome instead of the normal homologous pair (e.g., Down syndrome).

Monosomy

An aneuploid genetic disorder where a fertilized zygote is missing one homologous chromosome, possessing only a single copy.

Spermatogenesis

The production of male gametes in the testes, where a diploid spermatogonium undergoes meiosis and approximately equal cytokinesis to produce four small, motile, functional sperm.

Oogenesis

The production of female gametes in the ovaries, where a diploid oogonium undergoes meiosis with unequal cytokinesis, yielding one large, cytoplasm-rich egg cell and polar bodies.

Polar Body

A small, non-functional haploid cell produced during unequal cytokinesis in oogenesis that receives negligible cytoplasm and typically degenerates.

Prenatal Genetic Diagnostic Tests

Procedures including amniocentesis, chorionic villus sampling, and multiple marker screening performed during pregnancy (especially for older mothers) to assess the risk of fetal chromosomal abnormalities.