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cell division

reproduction of cells

cell cycle

the life of a cell from its origin in the division of a parent cell until its own division into two


a cell's endowment of DNA, its genetic information; prokaryotic ones are often a single long DNA molecule while eukaryotic ones usually consist of a number of DNA molecules


DNA are packaged into these which makes the replication and distribution of DNA more manageable; every eukaryotic species has a characteristic number of these

somatic cells

all body cells except reproductive cells; in humans contain 46 chromosomes each


sperm cells and egg cells (reproductive); in humans contain 23 chromosomes


a DNA-protein complex which is organized into a long, thin fiber. After a cell duplicates DNA in preparation for division; this fiber condenses and becomes densely coiled and folded, making the chromosomes shorter and so think we can see them with a light microscope

sister chromatids

two bodies containing identical copies of the chromosome's DNA molecule and are initially attached by proteins all along their lengths, later they are divided and become the new chromosomes


the place where sister chromatids narrow in their condensed form; a specialized "waist"


the division of the nucleus


the division of the cytoplasm


a variation of cell division which yields daughter cells that have half as many chromosomes as the parent cell; occurs only in the ovaries and testes

mitotic phase (M)

the shortest phase of the cell cycle in which the nucleus is divided and chromosomes are distributed into their nuclei; this phase includes both mitosis and cytokinesis


90% of the cell cycle in which the cell gros and copies its chromosomes in preparation for cell division; 3 subphases: G₁ phase, S phase, G₂ phase

G₁ phase

phase in which the cell grows by producing proteins and cytoplasmic organelles

S phase

synthesis phase in which chromosomes are duplicated

G₂ phase

phase in which the cell completes its preparations for division


chromatin fibers become more tightly coiled; nucleoli disappear; duplicated chromosome appears as sister chromatid; mitotic spindle begins to form; centrosomes move away from each other


nuclear envelope fragments so that the microtubules of spindle can now interact with the chromosomes; bundles of microtubules extend from each pole toward them middle of the cell; some microtubules attach to kinetochores causing chromosomes to begin jerky movements


a specialized structure located in the centromere region which, when attached to microtubule bundles, can cause jerky movements


centrosomes are now at opposite poles of the cell; chromosomes convene by their centromeres on the metaphase plate; kinetochores of sister chromatids are attached to microtubules coming from the opposite poles of the cell

metaphase plate

an imaginary plate that is equidistant between the spindle's two poles


begins suddenly; paired entromeres of each chromosome separate and sister chromatids are detached, each now a full chromosome; chromosomes move towards the opposite poles of of cell-centromeres first; poles of cell move farther apart a non-kinetochore microtubules lengthen; both poles have equivalent and complete collections of chromosomes

telophase and cytokinesis

nonkinetochore microtubules elongate the cell more and daughter nuclei form at the two poles of the cell; nuclear envelopes form from fragments of the parental nuclear envelope; chromatin fiber of each chromosome becomes less tightly coiled; mitosis is now complete; cytokinesis has usually already begin by now so two daughter cells appear shortly after mitosis; in animal cells, cytokinesis involves the formation of a cleavage furrow, which pinches the cell in two

mitotic spindle

a structure that consists of fibers made of microtubules and associated protiens which begins to form in the cytoplasm during prophase; spindle microtubules elongate by incorporating more subunits of the protein tubulin


a nonmembranous organelle that functions throughout the cell cycle to organize the cell's microtubules

cell plate

in plant cells, during telophase, vesciles from the Golgi move along microtubules to the middle of the cell where they coalesce to produce this and eventually fuse with the surrounding membrane to form a cell wall and two separate daughter cells

binary fission

prokaryotic cell division, "division in half"

origin of replication

copies of the first replicated region of prokaryotic DNA

cell cycle control system

a cyclically operating set of molecules in the cell that both triggers and coordinates key events in the cell cycle


a critical control point in the cell cycle where stop and go-ahead signals can regulate the cycle

G₀ phase

a nondividing state a cell enters if it does not receive a go-ahead signal at the G₁ checkpoint; most cells of the human body are in this phase


a protein that gets its name from its cyclically fluctuating concentration in the cell

cyclin-dependent kinases (Cdks)

kinases that drive the cell cycle and are actually present in constant concentration in the growing cell, but much of the time they are in inactive form-to be active, such a kinase needs to be attached to a cyclin

MPF (maturation-promoting factor)

a Cdk-cyclin complex that acts as an M-phase promoting factor because it triggers the cell's passage past the G2 checkpoint and into the M phase

growth factor

a protein released by certain body cells that stimulates other cells to divide

density-dependent inhibition

a phenomenon in which crowded cells stop dividing

anchorage dependence

a phenomenon in which in order to divide, cells must be attached to a substratum, such as inside a culture jar or the extracellular matrix of a tissue


the process that converts a normal cell to a cancer cell


a mass of abnormal cells within otherwise normal tissue

benign tumor

a tumor that does not cause serious problems and can be completely removed with surgery; a lump of abnormal cells that remain at the original site

malignant tumor

a tumor which becomes invasive enough to impair the functions of one or more organs; if you have this type of tumor, you are said to have cancer


the spread of cancer cells to locations distant from their original site


the transmission of traits from one generation to the next; inheritance


offspring differ somewhat in appearance from parents and siblings


the scientific study of heredity and hereditary variation


a unit of heredity


a gene's specific location along the length of a chromosome

asexual reproduction

a single individual is the sole parent and passes copies of all its genes to its offspring


a group of genetically identical individuals

sexual reproduction

two parents give rise to offspring that have unique combinations of genes inherited from the two parents

life cycle

the generation-to-generation sequence of stages in the reproductive history of an organism, from conception to production of its own offspring


a display of chromosomes arranged in pairs starting with the longest chromosomes

homologous chromosomes

chromosomes that make up a pair-that have the same length, centromere position, and staining pattern

sex chromosomes

X and Y


all the chromosomes that are not X and Y and therefore do not determine the sex of the organism

haploid cell

a cell with a single chromosome set


union of gametes-haploid sperm cell and haploid ovum


fertilized egg-the result of fertilization or syngamy

diploid cells

the zygote and all other cells having two sets of chromosomes

alternation of generations

a type of life cycle that includes both diploid and haploid multicellular stages


the multicellular diploid stage of the alternation of generations life cycle


haploid cells produced by meiosis in the sporophyte stage


the multicellular haploid stage of the alternation of generations life cycle

meiosis I

the first of the cell divisions in meiosis, which results in two haploid cells with replicated chromosomes

meiosis II

the second of the cell divisions in meiosis, which results in 4 haploid cells with unreplicated chromosomes


a process during prophase I of meiosis in which the duplicated chromosomes pair with their homologues


when four closely associated chromatids of a homologous pair are joined along their length by synapsis


x-shaped regions which represent a crossing of nonsister chromatids

nonsister chromatids

two chromatids belonging to separate but homologous chromosomes-physical manifestations of a genetic rearrangement called crossing over

crossing over

a process that produces recombinant chromosomes; begins very early in prophase I of meiosis

recombinant chromosomes

chromosomes that combine genes inherited from our two parents


a heritable feature, such as flower color, that varies among individuals


each variant for a character, such as purple or white color for flowers


when plants self-pollinate, all their offspring are of the same variety


the mating, or crossing, of two true-breeding varieties

P generation

true-breeding parents in hybridization

F₁ generation

the hybrid offspring of two true-breeding parents

F₂ generation

when F₁ hybrids self-pollinate, they produce this generation


alternate versions of a gene

dominant allele

a trait that is fully expressed in an organism's appearance

recessive allele

a trait that has no noticeable effect on the organism's appearance

law of segregation

two alleles for each character segregate during gamete production- ovum and sperm each only get one of the two alleles that are present in the somatic cells of the organism

Punnett square

a handy diagram for predicting the results of a genetic cross between individuals of known genotype


an organism who has a pair of identical alleles for a character


organisms who have two different alleles for a gene


an organism's traits-what it looks like and its physiological makeup


an organism's genetic makeup


the breeding of a recessive homozygote with an organism of dominant phenotype but unknown genotype


the F₁ hybrids produced in a cross in which only a single character is followed


an organism that is heterozygous for both characters being observed

Mendel's law of independent assortment

the independent segregation of each pair of alleles during gamete formation

incomplete dominance

when hybrids display appearances that are somewhere in between the phenotypes of the two parental varieties

complete dominance

when phenotypes of a heterozygote and dominant homozygote are indistinguishable


when two alleles affect the phenotype in separate, distinguishable ways


the ability of a gene to affect an organism in may ways


a situation in which a gene at one locus alters the phenotypic expression of a gene at a second locus

quantitative characters

characters that vary in the population along a continuum making an either-or classification impossible

polygenic inheritance

an additive effect of two or more genes on a single phenotypic character

norm of reaction

a range of phenotypic possibilities over which there may be variation due to environmental influence


when many factors, both genetic and environmental, collectively influence phenotype


as much information as possible is collected about a family's history for a particular trait, and this information is assembled into a family tree describing the interrelationships of parents and children across the generations


heterozygotes who are phenotypically normal with regard to a disorder but may transmit the recessive allele to their offspring


a technique used to extract amniotic fluid from the womb of an at least 14 week old fetus and tested for certain chemicals that can identify certain disorders

chorionic villus sampling

a test of the chorionic villi of the placenta (extracted through the cervix) used for karyotyping and certain biochemical tests

chromosome theory of inheritance

a theory that states that Mendelian genes have specific loci on chromosomes and it is the chromosomes that undergo segregation and independent assortment

wild type

the most common character, the phenotype most common in natural populations

sex-linked genes

genes located on a sex chromosome

linked genes

genes located on the same chromosome that tend to be inherited together in genetic crosses because the chromosome is passed along as a unit

genetic recombination

the general term for the production of offspring with new combinations of traits inherited from two parents

parental types

the phenotypes of the P generation plants; non-recombinants


offspring that show different phenotypes than the P generation

genetic map

an ordered list of the genetic loci along a particular chromosome

linkage map

a genetic map based on recombination frequencies

map units

one of these is equivalent to a 1% recombination frequency, often called centimorgans

cytological maps

maps of chromosomes which locate genes with respect to chromosomal features, such as stained bands, that can be seen in a microscope

Barr body

only one X chromosome is active in embryonic development of a female, the other becomes a compact object that lies along the inside of the nuclear envelope and are reactivated in the ovary cells that give rise to ova


an error in meiosis in which members of a pair of homologous chromosomes do not move apart properly during meiosis I or sister chromatids to separate during meiosis II, resulting in unequal distribution of homologues in gametes.


when a gamete receives an abnormal chromosome number


if a chromosome is present in triplicate in the fertilized egg


if a chromosome is missing in a fertilized egg


organisms that have more than two complete chromosome sets


when a chromosomal fragment lacking a centromere is lost during cell division


when a chromosomal fragment becomes attached as an extra segment to a sister chromatid


when a chromosomal fragment reattaches to the original chromosome but in the reverse orientation


when a chromosomal fragment joins a nonhomologous chromosome

genomic imprinting

when a gene on one chromosome is somehow silenced, while its allele on the homologous chromosome is left free to be expressed


proteins that are responsible for the first level of DNA packing in eukaryotic chromatin


the basic unit of DNA packing consisting of histone bead and its adjacent DNA

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