Test 3

anaphase

stage of mitosis during which sister chromatids are separated from each other

binary fission

prokaryotic cell division process

cell cycle

ordered series of events involving cell growth and cell division that produces two new daughter cells

cell plate

structure formed during plant cell cytokinesis by Golgi vesicles, forming a temporary structure (phragmoplast) and fusing at the metaphase plate; ultimately leads to the formation of cell walls that separate the two daughter cells

cell-cycle checkpoint

mechanism that monitors the preparedness of a eukaryotic cell to advance through the various cell-cycle stages

centriole

rod-like structure constructed of microtubules at the center of each animal cell centrosome

centromere

region at which sister chromatids are bound together; a constricted area in condensed chromosomes

chromatid

single DNA molecule of two strands of duplicated DNA and associated proteins held together at the centromere

cleavage furrow

constriction formed by an actin ring during cytokinesis in animal cells that leads to cytoplasmic division

condensin

proteins that help sister chromatids coil during prophase

cyclin

one of a group of proteins that act in conjunction with cyclin-dependent kinases to help regulate the cell cycle by phosphorylating key proteins; the concentrations of cyclins fluctuate throughout the cell cycle

cyclin-dependent kinase (Cdk)

one of a group of protein kinases that helps to regulate the cell cycle when bound to cyclin; it functions to phosphorylate other proteins that are either activated or inactivated by phosphorylation

cytokinesis

division of the cytoplasm following mitosis that forms two daughter cells.

diploid

cell, nucleus, or organism containing two sets of chromosomes (2n)

FtsZ

tubulin-like protein component of the prokaryotic cytoskeleton that is important in prokaryotic cytokinesis (name origin: Filamenting temperature-sensitive mutant Z)

G₀ phase

distinct from the G₁ phase of interphase; a cell in G₀ is not preparing to divide

G₁ phase

(also, first gap) first phase of interphase centered on cell growth during mitosis

G₂ phase

(also, second gap) third phase of interphase during which the cell undergoes final preparations for mitosis

gamete

haploid reproductive cell or sex cell (sperm, pollen grain, or egg)

gene

physical and functional unit of heredity, a sequence of DNA that codes for a protein.

genome

total genetic information of a cell or organism

haploid

cell, nucleus, or organism containing one set of chromosomes (n)

histone

one of several similar, highly conserved, low molecular weight, basic proteins found in the chromatin of all eukaryotic cells; associates with DNA to form nucleosomes

homologous chromosomes

chromosomes of the same morphology with genes in the same location; diploid organisms have pairs of homologous chromosomes (homologs), with each homolog derived from a different parent

interphase

period of the cell cycle leading up to mitosis; includes G₁, S, and G₂ phases (the interim period between two consecutive cell divisions)

karyokinesis

mitotic nuclear division

kinetochore

protein structure associated with the centromere of each sister chromatid that attracts and binds spindle microtubules during prometaphase

locus

position of a gene on a chromosome

metaphase

stage of mitosis during which chromosomes are aligned at the metaphase plate

metaphase plate

equatorial plane midway between the two poles of a cell where the chromosomes align during metaphase

mitosis

(also, karyokinesis) period of the cell cycle during which the duplicated chromosomes are separated into identical nuclei; includes prophase, prometaphase, metaphase, anaphase, and telophase

mitotic phase

period of the cell cycle during which duplicated chromosomes are distributed into two nuclei and cytoplasmic contents are divided; includes karyokinesis (mitosis) and cytokinesis

mitotic spindle

apparatus composed of microtubules that orchestrates the movement of chromosomes during mitosis

nucleosome

subunit of chromatin composed of a short length of DNA wrapped around a core of histone proteins

oncogene

mutated version of a normal gene involved in the positive regulation of the cell cycle

origin

(also, ORI) region of the prokaryotic chromosome where replication begins (origin of replication)

p21

cell-cycle regulatory protein that inhibits the cell cycle; its levels are controlled by p53

p53

cell-cycle regulatory protein that regulates cell growth and monitors DNA damage; it halts the progression of the cell cycle in cases of DNA damage and may induce apoptosis

prometaphase

stage of mitosis during which the nuclear membrane breaks down and mitotic spindle fibers attach to kinetochores

prophase

stage of mitosis during which chromosomes condense and the mitotic spindle begins to form

proto-oncogene

normal gene that when mutated becomes an oncogene

quiescent

refers to a cell that is performing normal cell functions and has not initiated preparations for cell division

retinoblastoma protein (Rb)

regulatory molecule that exhibits negative effects on the cell cycle by interacting with a transcription factor (E2F)

S phase

second, or synthesis, stage of interphase during which DNA replication occurs

septum

structure formed in a bacterial cell as a precursor to the separation of the cell into two daughter cells

telophase

stage of mitosis during which chromosomes arrive at opposite poles, decondense, and are surrounded by a new nuclear envelope

tumor suppressor gene

segment of DNA that codes for regulator proteins that prevent the cell from undergoing uncontrolled division

alternation of generations

life-cycle type in which the diploid and haploid stages alternate

chiasmata

(singular, chiasma) the structure that forms at the crossover points after genetic material is exchanged

cohesin

proteins that form a complex that seals sister chromatids together at their centromeres until anaphase II of meiosis

crossover

exchange of genetic material between nonsister chromatids resulting in chromosomes that incorporate genes from both parents of the organism

fertilization

union of two haploid cells from two individual organisms

gametophyte

a multicellular haploid life-cycle stage that produces gametes

germ cells

specialized cell line that produces gametes, such as eggs or sperm

interkinesis

(also, interphase II) brief period of rest between meiosis I and meiosis II

life cycle

the sequence of events in the development of an organism and the production of cells that produce offspring

meiosis

a nuclear division process that results in four haploid cells

meiosis I

first round of meiotic cell division; referred to as reduction division because the ploidy level is reduced from diploid to haploid

meiosis II

second round of meiotic cell division following meiosis I; sister chromatids are separated into individual chromosomes, and the result is four unique haploid cells

recombination nodules

protein assemblies formed on the synaptonemal complex that mark the points of crossover events and mediate the multistep process of genetic recombination between nonsister chromatids of a homologous pair

reduction division

nuclear division that produces daughter nuclei each having one-half as many chromosome sets as the parental nucleus; meiosis I is a reduction division

somatic cell

all the cells of a multicellular organism except the gametes or reproductive cells

spore

haploid cell that can produce a haploid multicellular organism or can fuse with another spore to form a diploid cell

sporophyte

a multicellular diploid life-cycle stage that produces haploid spores by meiosis

synapsis

formation of a close association between homologous chromosomes during prophase I

synaptonemal complex

protein lattice that forms between homologous chromosomes during prophase I, supporting crossover

tetrad

two duplicated homologous chromosomes (four chromatids) bound together by chiasmata during prophase I

allele

gene variations that arise by mutation and exist at the same relative locations on homologous chromosomes

autosomes

any of the non-sex chromosomes

blending theory of inheritance

hypothetical inheritance pattern in which parental traits are blended together in the offspring to produce an intermediate physical appearance

codominance

in a heterozygote, complete and simultaneous expression of both alleles for the same characteristic

continuous variation

inheritance pattern in which a character shows a range of trait values with small gradations rather than large gaps between them

dihybrid

result of a cross between two true-breeding parents that express different traits for two characteristics

discontinuous variation

inheritance pattern in which traits are distinct and are transmitted independently of one another

dominant

trait which confers the same physical appearance whether an individual has two copies of the trait or one copy of the dominant trait and one copy of the recessive trait

dominant lethal

inheritance pattern in which an allele is lethal both in the homozygote and the heterozygote; this allele can only be transmitted if the lethality phenotype occurs after reproductive age

epistasis

antagonistic interaction between genes such that one gene masks or interferes with the expression of another

F₁

first filial generation in a cross; the offspring of the parental generation

F₂

second filial generation produced when F₁ individuals are self-crossed or fertilized with each other

genotype

underlying genetic makeup, consisting of both physically visible and non-expressed alleles, of an organism

hemizygous

presence of only one allele for a characteristic, as in X-linkage; hemizygosity makes descriptions of dominance and recessiveness irrelevant

heterozygous

having two different alleles for a given gene on the homologous chromosome

homozygous

having two identical alleles for a given gene on the homologous chromosome

hybridization

process of mating two individuals that differ with the goal of achieving a certain characteristic in their offspring

incomplete dominance

in a heterozygote, expression of two contrasting alleles such that the individual displays an intermediate phenotype

law of dominance

in a heterozygote, one trait will conceal the presence of another trait for the same characteristic

law of independent assortment

genes do not influence each other with regard to sorting of alleles into gametes; every possible combination of alleles is equally likely to occur

law of segregation

paired unit factors (i.e., genes) segregate equally into gametes such that offspring have an equal likelihood of inheriting any combination of factors

linkage

phenomenon in which alleles that are located in close proximity to each other on the same chromosome are more likely to be inherited together

model system

species or biological system used to study a specific biological phenomenon to be applied to other different species

monohybrid

result of a cross between two true-breeding parents that express different traits for only one characteristic

P₀

parental generation in a cross

phenotype

observable traits expressed by an organism

product rule

probability of two independent events occurring simultaneously can be calculated by multiplying the individual probabilities of each event occurring alone

Punnett square

visual representation of a cross between two individuals in which the gametes of each individual are denoted along the top and side of a grid, respectively, and the possible zygotic genotypes are recombined at each box in the grid

recessive

trait that appears “latent” or non-expressed when the individual also carries a dominant trait for that same characteristic; when present as two identical copies, the recessive trait is expressed

recessive lethal

inheritance pattern in which an allele is only lethal in the homozygous form; the heterozygote may be normal or have some altered, nonlethal phenotype

reciprocal cross

paired cross in which the respective traits of the male and female in one cross become the respective traits of the female and male in the other cross

sex-linked

any gene on a sex chromosome

sum rule

probability of the occurrence of at least one of two mutually exclusive events is the sum of their individual probabilities

test cross

cross between a dominant expressing individual with an unknown genotype and a homozygous recessive individual; the offspring phenotypes indicate whether the unknown parent is heterozygous or homozygous for the dominant trait

trait

variation in the physical appearance of a heritable characteristic

X-linked

gene present on the X, but not the Y chromosome

aneuploid

individual with an error in chromosome number; includes chromosome segment deletions and duplications

autosome

any of the non-sex chromosomes

centimorgan (cM)

(also, map unit) relative distance that corresponds to a 0,01 recombination frequency

Chromosomal Theory of Inheritance

theory proposing that chromosomes are the genes' vehicles and that their behavior during meiosis is the physical basis of the inheritance patterns that Mendel observed

chromosome inversion

detachment, 180° rotation, and chromosome arm reinsertion

euploid

individual with the appropriate number of chromosomes for their species

homologous recombination

process by which homologous chromosomes undergo reciprocal physical exchanges at their arms, also crossing over

karyogram

a karyotype's photographic image

karyotype

an individual's chromosome number and appearance; includes the size, banding patterns, and centromere position

monosomy

otherwise diploid genotype in which one chromosome is missing

nondisjunction

failure of synapsed homologs to completely separate and migrate to separate poles during the meiosis' first cell division

nonparental (recombinant) type

progeny resulting from homologous recombination that exhibits a different allele combination compared with its parents

paracentric

inversion that occurs outside the centromere

parental types

progeny that exhibits the same allelic combination as its parents

pericentric

inversion that involves the centromere

polyploid

individual with an incorrect number of chromosome sets

recombination frequency

average number of crossovers between two alleles; observed as the number of nonparental types in a progeny's population

translocation

process by which one chromosome segment dissociates and reattaches to a different, nonhomologous chromosome

trisomy

otherwise diploid genotype in which one entire chromosome duplicates

X inactivation

condensing X chromosomes into Barr bodies during embryonic development in females to compensate for the double genetic dose