Chromosomes and Cellular Reproduction

Vocabulary flashcards covering key terms and concepts from Chapter 2: Chromosomes and Cellular Reproduction, Genetics: A Conceptual Approach (7th Edition).

Prokaryote

A unicellular organism lacking a nucleus and membrane-bound organelles, with DNA typically present as a single circular molecule not complexed with histones in bacteria. Cell diameter ranges from $1\,\mu\text{m}$ to $10\,\mu\text{m}$.

Eukaryote

An organism (unicellular or multicellular) whose cells contain a membrane-bound nucleus and organelles, with linear DNA closely complexed with histones. Cell diameter ranges from $10\,\mu\text{m}$ to $100\,\mu\text{m}$.

Virus

A non-prokaryotic, non-eukaryotic structure consisting of an outer protein coat surrounding a piece of nucleic acid (DNA or RNA).

Diploid

Refers to cells or organisms carrying two sets of genetic information organized as homologous pairs ($2n$).

Haploid

Refers to cells or organisms carrying a single set of genetic information ($n$).

Centromere

A constricted region of a chromosome where kinetochores form and spindle microtubules attach during division.

Telomeres

The stable ends or tips of a linear chromosome.

Origin of Replication

Specific site on a chromosome or DNA molecule where DNA synthesis begins.

Metacentric Chromosome

A chromosome whose centromere is located in the middle, creating two equal-sized arms.

Submetacentric Chromosome

A chromosome whose centromere is displaced toward one end, creating a distinct short arm and long arm.

Acrocentric Chromosome

A chromosome whose centromere is located near one end, producing a very short arm.

Telocentric Chromosome

A chromosome whose centromere is located at or very near the terminal end.

Interphase

An extended period between cell divisions during which cell growth, protein synthesis, DNA replication ($S$ phase), and preparation for division occur.

$G_1/S$ Checkpoint

A major decision point near the end of $G_1$ phase after which the cell is committed to dividing.

$G_2/M$ Checkpoint

A key transition checkpoint passed only if cell DNA is completely replicated and undamaged, allowing the cell to enter M phase.

Spindle-Assembly Checkpoint

A checkpoint during metaphase of mitosis that delays anaphase until all chromosomes are correctly aligned on the metaphase plate and attached to spindle fibers.

Prophase

The initial stage of mitosis where chromosomes condense (each consisting of two sister chromatids) and the mitotic spindle forms.

Prometaphase

The stage of mitosis during which the nuclear envelope disintegrates and spindle microtubules attach to chromatids at kinetochores.

Metaphase

The stage of mitosis in which individual chromosomes line up along the metaphase plate.

Anaphase

The stage of mitosis in which sister chromatids separate into individual chromosomes and migrate toward opposite spindle poles.

Telophase

The stage of mitosis where chromosomes arrive at spindle poles, the nuclear envelope re-forms, and condensed chromosomes relax.

Cytokinesis

The division of cytoplasm and organelles following mitosis or meiosis, forming separate daughter cells.

Meiosis I

The first division of meiosis, termed reduction division, where homologous chromosome pairs separate and chromosome number is reduced by half.

Meiosis II

The second division of meiosis, termed equational division, where sister chromatids separate into individual chromosomes.

Synapsis

The close pairing of homologous chromosomes during prophase I of meiosis.

Tetrad (Bivalent)

A structure consisting of four closely associated sister chromatids from a pair of synapsed homologous chromosomes.

Crossing Over

The exchange of genetic material between nonsister chromatids during prophase I of meiosis, creating new allele combinations.

Chiasmata

X-shaped sites where non-sister chromatids of homologous chromosomes cross over and maintain physical contact.

Leptotene

The first substage of prophase I in meiosis where chromosomes begin to condense and become visible.

Zygotene

The substage of prophase I in meiosis during which homologous chromosomes enter synapsis and pair up.

Pachytene

The substage of prophase I in meiosis where the synaptonemal complex forms and crossing over takes place.

Diplotene

The substage of prophase I in meiosis where the synaptonemal complex breaks down and chiasmata become clearly visible as homologs separate slightly.

Diakinesis

The final substage of prophase I in meiosis where chromosomes fully condense, nuclear membrane breaks down, and spindle forms.

Interkinesis

A period between meiosis I and meiosis II where the spindle breaks down, nuclear envelope re-forms, and chromosomes relax without undergoing DNA replication.

Cohesin

A protein complex that holds sister chromatids together and maintains homologous chromosome attachment at chiasmata during meiosis I.

Shugoshin

A protein that protects centromeric cohesin from breakdown during anaphase I of meiosis, preventing premature separation of sister chromatids until anaphase II.