D2.1 Cell & Nuclear Division

Cytokinesis

Division of cytoplasm forming two daughter cells at the end of mitosis or meiosis.

Cleavage furrow

The indentation that appears in animal cells during cytokinesis.

Contractile ring

Actin and myosin ring that pinches the cell membrane apart.

Cell plate

The new wall forming between plant cells during cytokinesis.

Equal cytokinesis

Produces two equal daughter cells.

Unequal cytokinesis

Produces one large cell (like an ovum) and small polar bodies.

Budding in yeast

Example of unequal cytokinesis.

Oogenesis

Process of egg formation through unequal cytokinesis.

Anucleate cells

Cells without nuclei that have limited lifespan.

Mitosis

Division that produces identical body cells with the same chromosome number.

Meiosis

Division that produces gametes with half the chromosome number.

Chromosome

Structure made of DNA wrapped around histone proteins.

Chromatid

One of two identical DNA strands joined by a centromere.

Cohesin loops

Hold sister chromatids together until anaphase.

Supercoiling

Wrapping of DNA around histones to condense chromosomes.

Histones

Proteins that help DNA coil and stay organized.

Kinetochore

Structure on centromeres where spindle fibers attach.

Spindle fibers

Microtubules that move chromosomes during division.

Interphase

Cell grows, performs functions, and replicates DNA (G1, S, G2).

Prophase

Chromosomes condense, spindle forms, and nuclear membrane breaks down.

Metaphase

Chromosomes line up in the middle of the cell.

Anaphase

Sister chromatids separate and move to opposite poles.

Telophase

Nuclear membranes form and chromosomes uncoil.

Reduction division

First meiotic division reducing chromosome number from diploid to haploid.

Crossing over

Exchange of DNA between homologous chromosomes; increases variation.

Independent assortment

Random alignment of chromosome pairs during meiosis I.

Non-disjunction

Error in meiosis when chromosomes fail to separate.

Cell proliferation

Increase in cell number for growth or repair.

Meristems

Plant regions (roots, shoots, buds) where mitosis happens often.

Cyclins

Proteins that control the cell cycle by activating certain stages.

Checkpoints

Points that make sure the cell is ready to move to the next stage.

G0 phase

Resting state when cells stop dividing.

Mutation

Change in DNA sequence that can alter cell function.

Proto-oncogene

Gene that can become cancer-causing when mutated.

Tumor suppressor gene

Gene that prevents uncontrolled cell division.

p53

Protein that stops the cell cycle when DNA is damaged.

Tumor

Group of abnormal cells that divide uncontrollably.

Benign tumor

Non-cancerous lump that doesn't spread.

Malignant tumor

Cancerous growth that can spread through the body.

Primary tumor

Original site where cancer cells start growing.

Secondary tumor

Tumor formed after cancer spreads from the original site.

Mitotic index

Proportion of cells undergoing mitosis

Homologous chromosomes

Pair of chromosomes with same genes but different alleles.

Diploid

Cell with two sets of chromosomes (2n).

Haploid

Cell with one set of chromosomes (n).

Prophase I

Chromosomes condense, crossing over happens between homologous pairs.

Metaphase I

Homologous pairs align randomly along the equator.

Anaphase I

Homologous chromosomes pulled to opposite poles.

Telophase I

Chromosomes reach poles, nuclear membranes form, and cytokinesis occurs.

Interkinesis

Short rest between meiosis I and II; no DNA replication.

Prophase II

Chromosomes condense again and new spindles form.

Metaphase II

Chromosomes align at equator again.

Anaphase II

Sister chromatids separate and move to poles.

Telophase II

Nuclear membranes form, chromosomes decondense, and four haploid cells result.