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Anaphase

Timeline: Stage of mitosis when sister chromatids separate

Binary fission

Prokaryotic cell division (one cell splits into two)

Cell cycle

Series of events between one cell division and the next

Cell cycle checkpoints

Control mechanisms ensuring a cell is ready to progress in the cycle

Cell plate

Plant cell structure forming during cytokinesis that becomes the new cell wall

Centriole

Microtubule-based rod structure in an animal cell's centrosome

Cleavage furrow

Indentation (actin ring) that pinches an animal cell in two during cytokinesis

Cytokinesis

Division of the cytoplasm to form two separate daughter cells

Diploid

Having two sets of chromosomes (2n)

FtsZ

Protein that forms a contractile ring at the future division site in a prokaryotic cell

G₀ phase

Resting phase of the cell cycle; cell is not preparing to divide

G₁ phase

First "gap" phase of interphase; cell grows

G₂ phase

Second "gap" phase of interphase; cell prepares for mitosis

Gamete

Haploid sex cell (sperm or egg)

Gene

Unit of heredity; a DNA sequence coding for a specific protein or RNA

Genome

Entire genetic content (DNA) of an organism

Haploid

Having a single set of chromosomes (n)

Homologous chromosomes

Pair of chromosomes with the same genes, one inherited from each parent

Interphase

Period between cell divisions (cell grows and DNA replicates)

Kinetochore

Protein structure at a chromosome's centromere where spindle fibers attach

Locus

Specific location of a gene on a chromosome

Metaphase

Stage of mitosis when chromosomes align at the cell's equator

Metaphase plate

Imaginary plane at the cell's center where chromosomes line up in metaphase

Mitosis

Nuclear division producing two identical nuclei (prophase-telophase)

Mitotic phase

Phase of the cell cycle when the cell divides (mitosis and cytokinesis)

Mitotic spindle

Microtubule apparatus that separates chromosomes during mitosis

Oncogene

Mutated gene that causes uncontrolled cell division (cancer)

Origin of replication

Site on a chromosome where DNA replication begins

Prometaphase

Mitosis stage when spindle fibers attach to kinetochores

Prophase

Mitosis stage when chromosomes condense and the spindle begins to form

Proto-oncogene

Normal gene regulating cell division; can mutate into an oncogene (cancer-causing)

Quiescent

Inactive (non-dividing) state of a cell

S phase

Synthesis phase of interphase; DNA replication occurs

Septum

Dividing wall that forms between prokaryotic daughter cells during division

Telophase

Final stage of mitosis when chromosomes decondense and new nuclei form

Tumor suppressor gene

Gene encoding a protein that prevents uncontrolled cell growth

Alternation of generations

Life cycle with alternating multicellular diploid and haploid stages

Aneuploid

Having an abnormal number of chromosomes (extra or missing)

Autosome

Any non-sex chromosome

Chiasma (pl. chiasmata)

X-shaped crossover point where homologous chromosomes exchange genetic material

Chromosome inversion

Reversal of a segment of a chromosome within the chromosome

Crossing over

Exchange of genetic material between homologous chromosomes during meiosis

Diploid-dominant

Life cycle in which the multicellular diploid stage is predominant

Euploid

Having the normal number of chromosomes for a species

Fertilization

Union of two haploid gametes to form a diploid zygote

Gametophyte

Haploid multicellular stage that produces gametes (in plants)

Germ cell

Cell that gives rise to gametes (egg or sperm)

Haploid-dominant

Life cycle in which the multicellular haploid stage is predominant

Interkinesis

Rest period between meiosis I and II (no DNA replication occurs)

Karyogram

Photographic image of an individual's chromosomes arranged in pairs

Karyotype

The number and appearance of an individual's chromosomes (size, shape, etc.)

Life cycle

Sequence of stages from one generation to the next in an organism's life

Meiosis I

First division of meiosis (homologous chromosomes separate; cells become haploid)

Meiosis II

Second division of meiosis (sister chromatids separate; results in four haploid cells)

Meiosis

Cell division producing four haploid cells (gametes), halving the chromosome number

Monosomy

Diploid genotype missing one chromosome (2n - 1)

Nondisjunction

Failure of chromosomes to separate properly during meiosis

Polyploid

Having more than two complete sets of chromosomes

Recombinant

Describing DNA or chromosomes with genetic material from two sources (parents)

Reduction division

Cell division that halves the number of chromosome sets (meiosis I)

Somatic cell

Any non-reproductive cell of a multicellular organism

Sporophyte

Diploid multicellular stage in plants that produces spores

Synapsis

Pairing of homologous chromosomes during prophase I of meiosis

Tetrad

Paired homologous chromosomes (four chromatids) during prophase I

Translocation

Attachment of a chromosome segment to a non-homologous chromosome

Trisomy

Diploid genotype with an extra chromosome (2n + 1)

X-inactivation

Condensation (silencing) of one X chromosome in females (Barr body formation)

Allele

One of two or more forms of a gene at a given locus on a chromosome

Codominance

In a heterozygote, both alleles are fully expressed (no blending)

Continuous variation

A range of small differences in a shared trait among individuals

Dihybrid

Offspring of two true-breeding parents differing in two traits

Discontinuous variation

Trait variations with only a few distinct, non-overlapping forms

Dominant

Describes an allele that masks another allele's effect in a heterozygote

Epistasis

One gene masks or interferes with the expression of another

F₁ generation

First filial generation; offspring of the parental (P) generation

F₂ generation

Second filial generation; offspring from crossing F₁ individuals

Genotype

An organism's genetic makeup (the allele combination it carries)

Hemizygous

Having only one allele for a gene (e.g. X-linked genes in human males)

Heterozygous

Having two different alleles for a given gene

Homozygous

Having two identical alleles for a given gene

Hybridization

Mating two individuals with different traits to produce offspring

Incomplete dominance

Heterozygote shows an intermediate phenotype (blended trait)

Law of dominance

In a heterozygote, one trait (dominant) conceals the presence of another (recessive)

Law of independent assortment

Alleles of different genes distribute independently into gametes

Law of segregation

Paired alleles separate equally into gametes during meiosis

Linkage

Genes close together on the same chromosome tend to be inherited together

Model system

Organism used to study biological processes, for insights applied to other species

Monohybrid

Offspring of two true-breeding parents differing in only one trait

P generation

Parental generation in a genetic cross

Phenotype

Observable traits of an organism

Punnett square

Grid diagram used to predict genetic cross outcomes

Recessive

Describes an allele whose effect is masked by a dominant allele

Reciprocal cross

Crosses performed in two directions, with the male and female traits swapped

Recombination

Exchange of genetic material between homologous chromosomes during meiosis

Test cross

Cross a dominant-phenotype individual (unknown genotype) with a homozygous recessive to determine the genotype

Trait

A specific inherited characteristic or feature of an organism

Wild type

The most common genotype or phenotype in a population

X-linked

A gene located on the X chromosome (not on the Y chromosome)