Cell Cycle, Checkpoints, Cancer, Meiosis, and Sex Determination (Vocabulary)

Vocabulary-style flashcards covering key terms from cell cycle checkpoints, cancer biology, meiosis, genetic variation, and sex determination discussed in the lecture.

G0 (G zero) state

A quiescent, inactive state where cells are not actively progressing through the cell cycle.

G1 checkpoint (restriction point)

A control point that checks whether conditions are favorable for cell division, including cell size, reserves, and DNA damage; if requirements aren’t met, the cell does not enter S phase.

G2 checkpoint

A control point at the end of G2 that ensures chromosomes have been replicated and are undamaged, and that the cell has adequate size and protein reserves before mitosis begins.

M checkpoint (spindle checkpoint)

A control point at the end of mitosis that ensures all sister chromatids are properly attached to the spindle apparatus before proceeding to cytokinesis.

Kinetochores

Protein structures at the centromeres that attach chromatids to spindle microtubules.

p53 (tumor suppressor protein)

A stress-activated protein that can arrest the cell cycle to allow DNA repair or trigger apoptosis if damage is severe.

DNA repair enzymes (DNA polymerase lambda and mu)

Enzymes recruited by p53 to repair damaged DNA before the cell cycle restarts.

Apoptosis

Programmed cell death; deliberate, orderly elimination of cells often due to irreparable damage.

Phagocytosis

Process by which macrophages engulf and digest dying or dead cells and debris.

Meiosis

Cell division in germ cells that produces four genetically diverse haploid gametes, reducing chromosome number by half.

Gametes

Haploid reproductive cells (egg and sperm) produced by meiosis.

Zygote

Diploid cell formed by fertilization of an egg by a sperm; contains two copies of each chromosome.

Fertilization

Union of two gametes to form a zygote, re-establishing the diploid chromosome number.

Haploid

Having one complete set of chromosomes (n).

Diploid

Having two complete sets of chromosomes (2n).

Diploid dominant life cycle

Life cycle in which the diploid stage is the longest and most common; meiosis produces haploid gametes later in the cycle.

Haploid dominant life cycle

Life cycle in which the haploid stage is the dominant, longstanding phase (common in some algae and fungi).

Homologous chromosomes

Chromosome pairs, one from each parent, that are similar in length and gene sequence.

Tetrad (bivalent)

Pair of homologous chromosomes each consisting of two sister chromatids that align during prophase I.

Synapsis

Pairing and physical connection of homologous chromosomes during prophase I.

Synaptonemal complex

Protein structure that holds homologous chromosomes together and facilitates crossing over during prophase I.

Crossing over

Exchange of DNA segments between non-sister chromatids of homologous chromosomes, creating genetic variation; occurs in prophase I.

Recombination

Formation of new combinations of alleles as a result of crossing over and independent assortment.

Chiasmata

Sites where crossing over occurs between homologous chromatids during meiosis.

Independent assortment

Random orientation of homologous chromosome pairs at metaphase I, producing diverse chromosome combinations.

Random fertilization

Unpredictable combination of which sperm fertilizes which egg, increasing genetic variation.

PMAT

Sequence of stages in cell division: Prophase, Metaphase, Anaphase, Telophase (applies to both meiosis and mitosis, with meiosis having two divisions).

Prophase I

Meiosis I stage where homologous chromosomes pair, crossing over occurs, and tetrads form.

Metaphase I

Meiosis I stage where tetrads align randomly at the metaphase plate before separation of homologs.

Meiosis I vs Meiosis II

Meiosis I reduces chromosome number by separating homologs; Meiosis II separates sister chromatids, yielding four unique haploid gametes.

Reduction division

Meiosis I; reduction of chromosome number from diploid to haploid by separating homologous chromosomes.

SRY gene

Sex-determining region Y on the Y chromosome; drives male development by regulating downstream genes (e.g., SOX9) to form testes.

SOX9

Gene regulated by SRY essential for testis differentiation and male development.

Sex determination (genetic vs environmental)

Genetic sex determination (XX/XY or ZZ/ZW) vs environmental sex determination (e.g., temperature in reptiles).

Male heterogamety

Males produce two different sex chromosomes (XY in humans); heterogametic sex.

Female heterogamety

Females produce two different sex chromosomes (e.g., ZW in birds); heterogametic sex.

Birds’ sex chromosomes (ZZ/ZW)

In birds, males are ZZ and females are ZW, reflecting female heterogamety.

XO

Sex chromosome system where males have a single X chromosome (and no second sex chromosome) in some species.

Haplodiploidy

Sex determination system where males are haploid (from unfertilized eggs) and females are diploid.

HeLa cells

Immortal human cancer cell line derived from Henrietta Lacks; widely used in biomedical research and discussions about ethics.