Cell Division, Meiosis, Chromosomal Inheritance, and Mendelian Genetics

Comprehensive vocabulary flashcards covering the cell cycle, mitosis, meiosis, chromosomal inheritance, and Mendelian genetics based on lecture slides.

Genome

The genetic material of an organism, encoded in its DNA.

Chromosome

A structure of nucleic acids and protein found in the nucleus of most living cells, consisting of one long linear DNA molecule associated with proteins that maintain structure and help control gene activity.

Genes

The units of information that specify an organism's inherited traits, consisting of a specific nucleotide sequence in DNA.

Chromatin

The entire complex of DNA and proteins that serves as the building material of eukaryotic chromosomes, making long DNA molecules compact.

Somatic Cells

All body cells of an organism except reproductive cells; human somatic cells contain $46$ chromosomes arranged in two sets of $23$.

Gametes

Reproductive cells (eggs and sperm) that contain half as many chromosomes as somatic cells; human gametes contain one set of $23$ chromosomes.

Sister Chromatids

Two identical copies of a duplicated chromosome attached at the centromere and connected along their lengths by cohesin protein complexes.

Centromere

A region of repetitive DNA sequences where a chromatid is attached most closely to its sister chromatid.

Mitosis

A process of nuclear division in eukaryotic cells divided into five stages (prophase, prometaphase, metaphase, anaphase, and telophase) that conserves chromosome number.

Cytokinesis

The division of the cytoplasm into two daughter cells, each the genetic equivalent of the parent cell, completing the mitotic phase.

Cell Cycle

An ordered sequence of events in the life of a cell, from its origin in the division of a parent cell until its own division into two.

Interphase

The period in the cell cycle where the cell is not dividing, comprising roughly $90\%$ of the cycle and divided into $G_1$, $S$, and $G_2$ phases.

$$G_1\text{ Phase}$$

The first gap, or growth phase, of interphase before DNA synthesis begins, characterized by metabolic activity and cell growth.

S Phase

The synthesis phase of the cell cycle during which metabolic activity, growth, and DNA replication take place.

$$G_2\text{ Phase}$$

The second gap, or growth phase, of interphase after DNA synthesis occurs, during which the cell completes preparations for division.

Mitotic Spindle

An assemblage of microtubules and associated proteins involved in the movement of chromosomes during mitosis.

Centrosome

A microtubule-organizing center in animal cells that contains a pair of centrioles at its center and organizes the mitotic spindle.

Aster

A radial array of short microtubules extending from each centrosome.

Kinetochore

A structure of proteins attached to the centromere that links sister chromatids to the spindle microtubules.

Metaphase Plate

An imaginary plane equidistant between the spindle poles where duplicated chromosomes align during metaphase.

Cleavage Furrow

A shallow groove that forms near the old metaphase plate in dividing animal cells, driven by an actin contractile ring that pinches the cell in two.

Cell Plate

A membrane-bounded flattened sac formed by the coalescence of Golgi vesicles at the midline of a dividing plant cell during cytokinesis.

Binary Fission

A method of asexual reproduction in prokaryotes and single-celled organisms in which a cell grows to double its size and divides into two identical cells.

Cell Cycle Control System

A cyclically operating set of molecules in eukaryotic cells that triggers and coordinates key events in the cell cycle.

Cyclin-Dependent Kinases (Cdks)

Protein kinases that activate or inactivate other target proteins by phosphorylation and require association with a cyclin to become active.

Cyclin

A cellular protein whose concentration fluctuates cyclically, thereby regulating the activity of cyclin-dependent kinases.

MPF (Maturation-Promoting Factor)

A cyclin-Cdk complex required for a cell to pass the $G_2$ checkpoint and enter the mitotic phase.

$$G_0\text{ Phase}$$

A nondividing state entered by cells that do not receive a go-ahead signal at the $G_1$ checkpoint; most human cells exist in this state.

Growth Factor

A protein released by certain cells that stimulates other cells to divide, such as platelet-derived growth factor (PDGF).

Density-Dependent Inhibition

A phenomenon in which crowded animal cells stop dividing once a monolayer forms.

Anchorage Dependence

The requirement that animal cells must be attached to a solid substratum or extracellular matrix to initiate cell division.

Benign Tumor

A localized mass of abnormal cells that remains at its site of origin without invading neighboring tissues.

Malignant Tumor

A cancerous mass of cells whose genetic and cellular alterations enable them to spread to new tissues and impair organ functions.

Heredity

The biological transmission of traits from parents to offspring from one generation to the next.

Variation

Differences in physical and genetic traits between members of the same species.

Genetics

The scientific study of heredity and hereditary variation.

Locus

A gene's specific physical location along the length of a chromosome.

Asexual Reproduction

The generation of offspring from a single parent without the fusion of gametes, producing genetically identical clones via mitosis.

Sexual Reproduction

Reproduction arising from the fusion of two gametes, producing offspring with unique combinations of genes inherited from both parents.

Karyotype

A microscopic display of the complete set of condensed chromosome pairs of a cell, arranged by length, centromere position, and banding pattern.

Homologous Chromosomes

A pair of chromosomes of the same length, centromere position, and staining pattern that carry genes for the same inherited characters at corresponding loci.

Autosomes

Chromosomes that are not directly involved in sex determination; in humans, chromosome pairs 1 through 22.

Sex Chromosomes

Chromosomes that determine the biological sex of an individual, represented by the X and Y chromosomes in humans.

Haploid Cell ($n$)

A cell containing a single set of chromosomes ($n = 23$ in humans), such as a gamete.

Diploid Cell ($2n$)

A cell containing two sets of chromosomes ($2n = 46$ in humans), one set inherited from each parent, such as a somatic cell.

Fertilization

The union of a haploid sperm and a haploid egg resulting in the restoration of a diploid zygote.

Zygote

The diploid fertilized egg formed by the fusion of male and female gametes.

Meiosis

A specialized cell division in sexually reproducing organisms consisting of two rounds of division (Meiosis I and II) but only one round of DNA replication, yielding four haploid daughter cells.

Synapsis

The pairing and physical side-by-side connection of duplicated homologous chromosomes during prophase I of meiosis.

Crossing Over

The reciprocal exchange of genetic material between nonsister chromatids of homologous chromosomes during prophase I of meiosis.

Chiasmata

X-shaped anatomical regions on homologous pairs where crossing over has occurred between nonsister chromatids.

Recombinant Chromosomes

Individual chromosomes produced by crossing over that carry combined DNA and allele combinations derived from two distinct parents.

Independent Assortment

The random orientation and segregation of maternal and paternal homologous pairs at the metaphase plate in meiosis I, creating $2^n$ possible combinations in gametes.

Random Fertilization

The random fusion of any single male gamete with any single female gamete, producing approximately $70\text{ trillion}$ ($2^{23} \times 2^{23}$) possible diploid combinations in humans.

Chromosome Theory of Inheritance

A fundamental biological theory developed by Walter Sutton and Theodor Boveri stating that genes are located at specific loci on chromosomes and that chromosome behavior during meiosis accounts for inheritance patterns.

Wild Type

The phenotype most commonly observed in natural populations for a character, designated by a superscript plus sign ($w^+$), such as red eyes in Drosophila.

Mutant Phenotype

Traits that represent alternatives to the wild type, originating from mutations in the wild-type allele, such as white eyes ($w$) in Drosophila.

Sex-Linked Gene

A gene located on either sex chromosome (the X or Y chromosome).

X-Linked Gene

A gene located on the human X chromosome, which contains approximately $1{,}100$ genes.

Y-Linked Gene

A gene located on the human Y chromosome, which contains about $78$ genes coding for approximately $25$ proteins.

SRY

A gene located on the human Y chromosome that triggers the development of testes in the embryo.

WNT4

A human gene that encodes a protein promoting female gonad (ovary) development.

Hemizygous

The state of possessing only one copy of an allele or gene, characteristic of human males for X-linked loci.

Duchenne Muscular Dystrophy

A human sex-linked recessive disorder characterized by progressive muscle weakening and loss of coordination due to the absence of the key protein dystrophin.

Hemophilia

An X-linked recessive genetic disorder characterized by excessive bleeding following injury due to the lack of one or more blood-clotting proteins.

Barr Body

A dense, condensed object lying along the inside of the nuclear envelope in female mammalian cells, representing a randomly inactivated X chromosome.

Linked Genes

Genes located sufficiently close together on the same chromosome that they tend to be inherited together as a unit rather than assorting independently.

Parental Types

Offspring exhibiting phenotypic trait combinations that match one of the original true-breeding parental phenotypes.

Recombinant Types

Offspring exhibiting phenotypic combinations of traits that differ from those found in either parental generation parent.

Linkage Map

A genetic map based on recombination frequencies that displays the relative linear order and distances of genes along a chromosome.

Map Unit

A unit of measurement for distance along a chromosome, equivalent to a $1\%$ recombination frequency between linked loci.

Nondisjunction

An error during meiosis or mitosis in which homologous chromosomes or sister chromatids fail to separate properly into daughter cells.

Aneuploidy

A chromosomal condition in which a zygote has an abnormal number of a particular chromosome, including monosomy ($2n - 1$) and trisomy ($2n + 1$).

Polyploidy

A chromosomal condition in which an organism possesses more than two complete chromosome sets, such as triploidy ($3n$) or tetraploidy ($4n$).

Deletion

A mutational structural alteration in which a chromosomal fragment is lost.

Duplication

A chromosomal alteration in which a broken chromosomal fragment reattaches as an extra segment to a sister or nonsister chromatid.

Inversion

A chromosomal alteration in which a broken fragment reverses its orientation before reattaching to the same chromosome.

Translocation

A chromosomal alteration in which a broken fragment joins a nonhomologous chromosome, commonly in a reciprocal exchange.

Down Syndrome (Trisomy 21)

An aneuploid human condition resulting from an extra copy of chromosome 21 ($47$ total chromosomes), leading to characteristic physical features, heart defects, and developmental delays.

Klinefelter Syndrome

An aneuploidy of sex chromosomes in human males resulting from an extra X chromosome ($47\text{, XXY}$), leading to small testes, reduced sperm production, and taller height.

Turner Syndrome (Monosomy X)

A sex chromosome aneuploidy in human females lacking a second sex chromosome ($45\text{, X0}$), leading to sterility due to immature reproductive organs.

Cri du Chat

A human genetic disorder caused by a specific deletion on chromosome 5, resulting in severe intellectual disability, microcephaly, and a cat-like infant cry.

Philadelphia Chromosome

An abnormally short translocated chromosome 22 created by reciprocal exchange with chromosome 9, creating an oncogenic fusion gene that drives chronic myelogenous leukemia (CML).

Character

A heritable feature that varies among individuals, such as flower color in garden pea plants.

Trait

Each variant for a specific heritable character, such as purple or white flower color.

True-Breeding

Referring to organisms that consistently produce offspring with the same phenotype across generations of self-pollination.

Hybridization

The mating or crossing of two distinct true-breeding varieties.

P Generation

The true-breeding (homozygous) parental individuals from which hybrid offspring are initially generated.

$$F_1\text{ Generation}$$

The first filial generation; hybrid heterozygous offspring resulting directly from a cross between true-breeding parents.

$$F_2\text{ Generation}$$

The second filial generation; offspring produced by the self-pollination or interbreeding of individuals from the $F_1$ generation.

Allele

Any of the alternative versions of a gene that account for variations in inherited characters.

Dominant Allele

An allele that is fully expressed in the phenotype of a heterozygote, masking the presence of a recessive allele.

Recessive Allele

An allele whose phenotypic effect is not observed in a heterozygote when a dominant allele is present.

Law of Segregation

Mendel's first law stating that two alleles for a heritable character segregate during gamete formation and end up in different gametes.

Punnett Square

A grid diagram used to calculate and predict the allele combinations and phenotypic ratios of offspring from a cross between known genotypes.

Homozygote

An organism that possesses a pair of identical alleles for a given gene (e.g., $PP$ or $pp$).

Heterozygote

An organism that possesses two different alleles for a given gene (e.g., $Pp$).

Phenotype

The observable physical and physiological appearance and traits of an organism, determined by its genotype.

Genotype

The complete genetic makeup or set of alleles present in an organism.

Testcross

The breeding of an individual with an unknown genotype expressing a dominant phenotype with a homozygous recessive individual to determine the unknown genotype.