BIO 1001 exam 3

Reductive Division

The type of cell division that occurs during meiosis where the chromosome number is halved, transitioning a cell from diploid ($2n$) to haploid ($1n$).

Crossing Over

The exchange or swapping of genetic material between homologous chromosomes that occurs during prophase I of meiosis I following bivalent (tetrad) formation.

Anaphase I

The specific stage of meiosis I during which homologous chromosomes separate and move toward opposite poles of the cell.

Anaphase II

The stage of meiosis II during which sister chromatids are separated in a haploid cell.

Asexual Reproduction

A form of reproduction involving only one parent that produces genetically identical offspring (clones) via mitotic divisions without the formation or fusion of gametes.

Sexual Reproduction

A form of reproduction involving two parents in which haploid gametes produced by meiosis fuse to create a genetically unique diploid zygote.

Gene

A sequence within DNA that codes for specific characteristics and traits, passed along from generation to generation.

Diploid-Dominant Life Cycle

A sexual life cycle where the multicellular organism is diploid for the majority of its lifespan (common in most animals), and the only haploid stage consists of specialized gametes.

Haploid-Dominant Life Cycle

A sexual life cycle typical of fungi where the multicellular organism is haploid and produces spores; the brief diploid zygote immediately undergoes meiosis to regenerate haploid spores.

Alternation of Generations

A sexual life cycle common in plants and some algae that alternates between a multicellular diploid generation and a multicellular haploid generation.

Sporophyte

The multicellular diploid ($2n$) organism in an alternation of generations life cycle that produces haploid spores through meiosis.

Gametophyte

The multicellular haploid ($1n$) organism in an alternation of generations life cycle that produces haploid gametes through mitosis.

Wild Type

The most common or normally seen characteristic, chromosomal structure, or chromosomal number observed in nature for a given species.

Metacentric

A chromosome structure where the centromere is positioned right in the middle.

Submetacentric

A chromosome structure where the centromere is located slightly off-center.

Acrocentric

A chromosome structure where the centromere is located near one end of the chromosome.

Cumulocentric

A chromosome structure where the centromere is positioned at the very end of the chromosome.

$p$ Arm and $q$ Arm

The structural designation of chromosome arms in a karyotype, where $p$ (petite) denotes the shorter arm arranged at the top, and $q$ denotes the longer arm arranged at the bottom.

Giasma Stain

A specialized staining dye that binds to adenine and thymine base pairs, producing distinct dark purple banding patterns useful for identifying chromosomes and detecting mutations.

Mutation

A heritable change in genetic material that can be passed down to subsequent cell generations or offspring.

Chromosomal Deletion

A structural mutation characterized by the loss or absence of a segment of genetic material, reducing the overall length of the chromosome.

Chromosomal Duplication

A structural mutation where a segment of genetic material is replicated, resulting in extra copies and an increase in total genetic material.

Chromosomal Inversion

A structural mutation in which a segment of DNA is flipped or inverted in orientation, altering the order of genetic material without changing the total amount.

Simple Translocation

A chromosomal alteration where a piece of one chromosome breaks off and attaches to a different non-homologous chromosome.

Reciprocal Translocation

A chromosomal alteration where two non-homologous chromosomes mutually exchange or swap segments of genetic material with each other.

Euploid

An organism or cell possessing an exact multiple of the complete chromosome set, such as haploid ($1n$) or diploid ($2n$).

Polyploidy

A chromosomal variation in which an organism possesses more than two complete sets of chromosomes, such as triploid ($3n$) or tetraploid ($4n$).

Aneuploidy

A chromosomal condition in which the number of chromosomes is abnormal due to an extra or missing chromosome in a specific set.

Monosomy

An aneuploid state represented as $2n - 1$, where an individual is missing one chromosome from a homologous pair.

Trisomy

An aneuploid state represented as $2n + 1$, where an individual possesses three copies of a specific chromosome instead of the normal two.

Nondisjunction

The failure of homologous chromosomes or sister chromatids to separate properly during cell division (mitosis or meiosis), producing daughter cells with abnormal chromosome numbers.

Autosomes

Non-sex chromosomes; in humans, there are 22 pairs (22 distinct types) present in somatic cells.

Turner Syndrome

A human sex-chromosome monosomy condition characterized by the presence of only a single $X$ chromosome.

Triple X Syndrome

A human sex-chromosome trisomy condition where an individual possesses three $X$ chromosomes instead of two.

Trisomy 21

A viable autosomal trisomy condition in humans characterized by having one extra copy of chromosome 21 ($2n + 1$).

Mitosis

A process of equal cell division starting with one parent cell and ending with two genetically identical daughter cells with the same ploidy.

Interphase

The period prior to mitosis comprising G1, S, and G2 phases, accounting for $90\%$ of the cell's life cycle, during which the cell performs metabolic processes, makes proteins, and duplicates DNA.

S Phase

The specific phase within interphase where DNA replication occurs, resulting in duplicated chromosomes prior to the start of cell division.

Diploid ($2n$)

A cellular state in which there are two of each size or type of chromosome, with one set inherited from each parent.

Haploid ($1n$)

A cellular state containing only one chromosome of each size or type, as seen in gametes.

Sister Chromatids

Two identical copies of a duplicated chromosome joined together in an X shape that are separated during anaphase of mitosis and anaphase II of meiosis.

Centrosome

The specific microtubule organizing center found in animal cells that duplicates and moves to opposite poles during prophase.

Mitotic Spindle

An apparatus composed of microtubules that forms between centrosomes to organize, align, and sort chromosomes during cell division.

Astral Microtubules

Microtubules of the spindle apparatus that attach to the plasma membrane to anchor the centrosome down at the pole of the cell.

Polar Microtubules

Microtubules of the spindle apparatus that define the metaphase plate, separate the two poles, and push against each other to lengthen the cell during division.

Kinetochore Microtubules

Microtubules of the spindle apparatus that attach to kinetochore proteins on chromatids and shorten to pull chromosomes toward opposite poles.

Metaphase Plate

The equatorial plane or center of the cell along which chromosomes align during metaphase.

Cleavage Furrow

A cytoskeletal structure in dividing animal cells that constricts like a drawstring to pinch the cytoplasm into two daughter cells during cytokinesis.

Cell Plate

A structure formed during cytokinesis in plant cells by Golgi-derived vesicles assembling at the center to create a new dividing membrane between daughter cells.

Cytokinesis

The physical division of the cytoplasm following nuclear division that separates the daughter cells.

Somatic Cells

All body cells other than sex cells; in wild-type humans, they are diploid ($2n = 46$) and contain 23 pairs of chromosomes.

Gametes

Haploid sex cells (egg and sperm) containing 23 chromosomes ($1n = 23$) in wild-type humans.

Autosomal Chromosomes

Non-sex chromosomes, consisting of 22 pairs in human somatic cells.

Sex Chromosomes

Chromosomes that determine the sex of an organism; represented by one pair in human somatic cells (XX in typical females, XY in typical males).

Meiosis

A reductive division process involving two rounds of division that starts with a diploid cell and yields four genetically unique haploid cells.

Meiosis I

The first division round of meiosis that separates homologous chromosomes, reducing the ploidy from diploid ($2n$) to haploid ($1n$) with duplicated DNA.

Meiosis II

The second division round of meiosis, immediately following meiosis I without an intervening interphase, which separates sister chromatids to produce four non-duplicated haploid cells.

Bivalent (Tetrad)

An association formed during prophase I when two pairs of homologous sister chromatids come together and associate.

Synaptonemal Complex

A glue-like protein structure formed during synapsis that seals and attaches homologous sister chromatids together into a bivalent.

Crossing Over

The controlled reciprocal exchange of genetic material between homologous non-sister chromatids occurring exclusively in prophase I.

Chiasma

The specific physical attachment site between homologous chromosomes where the swapping of genetic material occurs during crossing over.

Random Alignment

The independent orientation of homologous chromosome pairs along the metaphase plate in a double row during metaphase I, yielding $2^n$ possible combinations (over $8{,}000{,}000$ in humans).

DNA Polymerase III

The primary enzyme responsible for synthesizing new DNA strands in both the leading and lagging strands, possessing a proofreading function to maintain high replication fidelity.

Proofreading (DNA Polymerase III)

The corrective mechanism in which DNA polymerase III detects a mismatched base, reverses direction to move from $3'$ to $5'$ to remove the incorrect nucleotides, and then resumes synthesis in the $5'$ to $3'$ direction.

Chromatin

The less condensed form of genetic material where DNA is wrapped around histone proteins to form nucleosomes, allowing genes to be actively expressed.

Chromosome

A cellular structure composed of highly condensed DNA double helix that packages and stores genetic material.

Sister Chromatids

Two identical copies of a replicated chromosome produced during DNA replication and physically joined at the centromere.

Centromere

The specific region of a duplicated chromosome that physically links and holds sister chromatids together.

Kinetochore Proteins

Proteins located on sister chromatids that attach to cytoskeletal elements (microtubules) to assist in separating chromatids to opposite ends of the cell during division.

Euchromatin

A decondensed form of genetic material found before DNA replication that enables gene expression, transcription, and translation.

Heterochromatin

The highly condensed form of genetic material visible under a microscope during division, packaged tightly to ensure efficient and accurate chromosome distribution.

Homologous Chromosomes

Pairs of chromosomes (one maternal and one paternal) that share the same size and gene locations but are not identical because they can contain different alleles or variations.

Locus (plural: Loci)

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

Allele

A specific variation of a gene found at a given locus on a chromosome (e.g., dominant or recessive variants).

Ploidy

The number of chromosomes present per set or type within a cell, represented by the lowercase letter $n$.

Haploid

A cell condition characterized by having only one chromosome of each set or type ($1n$ or $n$), exemplified by gametes.

Diploid

A cell condition characterized by having two chromosomes of each set or type ($2n$), exemplified by somatic cells.

Karyotype

A visual representation showing all chromosomes present in an actively dividing cell, organized by size and type.

Autosomal Chromosomes

The non-sex chromosomes, numbered 1 through 22 in humans, present in 22 pairs within somatic cells.

Gametes

Haploid reproductive sex cells (eggs and sperm) that carry $23$ individual chromosomes in humans.

Somatic Cells

Non-reproductive body cells (such as skin, liver, or muscle cells) that are diploid, carrying 23 pairs for a total of $46$ chromosomes in humans.

Interphase

The longest stage of a cell's life span comprising the $G_1$, $S$, and $G_2$ phases, during which a cell carries out regular metabolic duties and prepares for division.

$G_1$ Phase (First Gap Phase)

The longest phase of the cell cycle where the cell performs daily metabolic functions, synthesizes proteins, and evaluates environmental and signaling factors to decide whether to divide.

$S$ Phase (Synthesis Phase)

The interphase stage where DNA replication occurs, transforming unduplicated chromosomes into duplicated chromosomes composed of sister chromatids without altering total chromosome number.

$G_2$ Phase (Second Gap Phase)

The final stage of interphase preceding mitosis where the cell replicates necessary organelles and synthesizes proteins required for chromosome sorting.

$M$ Phase

The cell cycle division phase composed of mitosis (nuclear sorting of genetic material) immediately followed by cytokinesis (division of the cytoplasm).

$G_0$ Phase ($G_{\text{naught}}$)

A quiescent detour or resting state outside the active cell division cycle where non-dividing cells remain temporarily or permanently (such as neurons).

$G_1$ Checkpoint

A regulatory transition point before the $S$ phase that evaluates environmental conditions, growth factors, and checks for DNA damage before allowing DNA replication to start.

$G_2$ Checkpoint

A regulatory transition point prior to mitosis that verifies DNA has replicated completely and accurately and confirms that organelle preparations are complete.

$M$ Checkpoint (Spindle Apparatus Checkpoint)

A regulatory checkpoint occurring during metaphase that ensures kinetochore microtubules are properly attached and aligned to guarantee equal distribution of sister chromatids.

Cyclins

Regulatory proteins whose intracellular concentrations fluctuate cyclically across the cell cycle, binding specific CDKs to trigger progression past checkpoints.

Cyclin-Dependent Kinases (CDKs)

Protein kinases whose overall cellular concentrations remain constant, requiring binding to specific cyclins to become enzymatically active and phosphorylate downstream target proteins.

Cyclin-CDK Complex

The active molecular complex formed by the binding of a specific cyclin to its corresponding CDK partner, which phosphorylates proteins to turn checkpoint signals green.

mRNA (Messenger RNA)

The type of RNA that is read by ribosomes to produce polypeptide chains during translation.

rRNA (Ribosomal RNA)

The type of RNA present within the subunits of ribosomes.

tRNA (Transfer RNA)

The RNA that acts as a bridge to bring the correct amino acid to the growing polypeptide chain during translation.

Four Criteria of Genetic Material

The essential requirements that genetic material must fulfill: information storage, replication, transmission, and variation.

Smooth Streptococcus pneumoniae

A bacterial strain surrounded by a polysaccharide capsule that evades the immune system and causes pneumonia.

Rough Streptococcus pneumoniae

A bacterial strain that lacks a polysaccharide capsule, is easily detected and destroyed by the immune system, and does not cause pneumonia.

Transformation

The process demonstrated by Griffith in which genetic material from heat-killed bacteria transforms a living rough strain into a living smooth strain.