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all of the changes that have transformed life over an immense time


an inherited characteristic that improves an organism's ability to survive and reproduce in a particular environment

descent with modification

process by which descendants of ancestral organisms spread into various habitats and accumulate adaptations to diverse ways of life

natural selection

process by which individuals with inherited characteristics well-suited to the environment leave more offspring than do other individuals


preserved remains or marking left by an organism that lived in the past

fossil record

chronological collection of life's remains in sedimentary rock layers


species that no longer exists

homologous structures

structure found in more than one species that share a common ancestor

vestigial structure

remnant of a structure that may have had an important function in a species' ancestors, but has no clear function in the modern species


a group of individuals of the same species living in the same area at the same time


refers to differences among members of the same species

artificial selection

the selective breeding of domesticated plants and animals to produce offspring with genetic traits that humans value

gene pool

all of the alleles in all the individuals that make up a population


a generation-to-generation change in the frequencies of alleles within a population

Hardy-Weinberg equilibrium

condition that occurs when the frequency of alleles in a particular gene pool remain constant over time

genetic drift

change in the gene pool of a population due to chance

gene flow

exchange of genes between populations


contribution that an individual makes to the gene pool of the next generation compared to the contributions of other individuals (ability to reproduce)


medicine that kills or slows the growth of bacteria

biological species concept

definition of a species as a population or group of populations whose members can breed with one another in nature and produce fertile offspring


major biological changes evident in the fossil record


formation of new species

reproductive isolation

condition in which a reproductive barrier keeps two species from interbreeding

geographic isolation

separation of populations as a result of geographic change or migration to geographically isolated places

adaptive radiation

evolution from a common ancestor of many species adapted to diverse environments

punctuated equilibrium

evolutionary model suggesting species often diverge in spurts of relatively rapid change, followed by long periods of little change


study of multicellular organisms as they develop from fertilized eggs to fully formed organisms

geologic time scale

Earth's history organized into four eras: Precambrian, Paleozoic, Mesozoic, and Cenozoic

radiometric dating

determination of absolute ages of rocks and fossils through calculations based on a radioactive isotope's fixed rate of decay


time it takes for 50 percent of a radioactive isotope sample to decay

continental drift

motion of continents about Earth's surface on plates of crust floating on the hot mantle

mass extinction

episode of great species loss


identification, naming, and classification of species


two-part Latin name of a species

phylogenetic tree

branching diagram, suggesting evolutionary relationships, that classifies species into groups within groups

convergent evolution

process in which unrelated species from similar environments have adaptations that seem very similar

analogous structures

similarities among unrelated species that result from convergent evolution

derived character

homologous characteristic that unites organisms as a group


phylogenetic tree constructed from a series of two-way branch points, suggesting ancestral relationships among species


complete set of an organism's genetic material


small protein that dna wraps around

trisomy 21

condition in which an individual has three number 21 chromosomes, resulting in down syndrome

down syndrome

general set of symptoms in people with trisomy 21


event during meiosis in which homologous chromosomes or sister chromatids fail to separate


change to a chromosome in which part of the chromosome is repeated


change to a chromosome in which a fragment of the chromosome is removed


change to a chromosome in which a fragment of the original chromosome is reversed


change to a chromosome in which a fragment of one chromosome attaches to a nonhomologous chromosome


genetic element that moves from one location to another in a genome


family tree that records and traces the occurrence of a trait in a family


individual who has one copy of the allele for a recessive disorder and does not exhibit symptoms

genetic counselor

person trained to collect, analyze, and explain data about human inheritance patterns

growth factor

protein that initiates cell division

tumor-suppressor gene

gene that codes for a protein that stops cell division in particular situations


cancer-causing gene

recombinant DNA technology

technology that combines genes from different sources into a single DNA molecule


small, circular DNA molecule found in bacteria that is separate from the bacterial chromosome

restriction enzyme

enzyme that cuts sugar-phosphate bonds in the DNA backbone at specific points within particular nucleotide sequences in DNA

genomic library

complete collection of cloned DNA fragments from an organism

nucleic acid probe

radioactively labeled nucleic acid molecule used to tag a particular DNA sequence

genetically modified organism (GMO)

organism that has acquired genetic material by artificial means


genetically modified organism whose source of new genetic material is a different species

polymerase chain reaction (PCR)

technique that makes many copies of a certain segment of DNA without using living cells

gel electrophoresis

technique for sorting molecules or fragments of molecules by length

genetic marker

specific portion of DNA that varies among individuals

DNA fingerprint

an individual's unique banding pattern on an electrophoresis gel, determined by restriction fragments of the person's DNA


cluster of genes and their control sequences


control sequence on an operon where RNA polymerase attaches to the DNA


control sequence on an operon that acts as a switch, determining whether or not RNA polymerase can attach to the promoter


protein that binds to the operator and blocks attachment of RNA polymerase to the promoter

transcription factor

protein that regulates transcription by binding to promoters or to RNA polymerases

gene expression

transcription and translation of genes into proteins

cellular differentiation

increasing specialization in structure and function of cells during development of a multicellular organism

stem cell

cell with the potential to develop into one of several types of differentiated cells

homeotic gene

master control gene in many organisms that directs development of body parts


a variation of a particular inherited character


the study of heredity

cross fertilization

when sperm from the pollen of one flower fertilizes the eggs in the flower of a different plant


the offspring of two different true-breeding varieties

monohybrid cross

a pairing in which the parent plants differ in only one character


when two of your alleles are the same for a certain characteristic


when two of your alleles are different for a certain characteristic


an allele in a heterozygous individual that appears to be the only one affecting that trait


an allele in a heterozygous individual that doesn't appear to affect a trait

punnett square

a type of diagram that shows all possible outcomes of a genetic cross


an observable trait, the physical appearance


the genetic makeup, or combination of alleles


breeds an individual of unknown genotype, but dominant phenotype with a homozygous recessive individual

dihybrid cross

crossing organisms differing in two characters


inheritance pattern in which a heterozygote expresses the distinct traits of both alleles

polygenic inheritance

when two or more genes affect a single character

chromosome theory of inheritance

generalization that genes are located on chromosomes and that the behavior of chromosomes during meiosis and fertilization accounts for inheritance patterns

gene locus

specific location of a gene on a chromosome

genetic linkage

the tendency for the alleles on one chromosome to be inherited together

sex-linked gene

gene located on a sex chromosome


package of nucleic acid wrapped in a protein coat that must use a host cell's machinery to reproduce itself


virus that infects bacteria

deoxyribonucleic acid (DNA)

molecule responsible for inheritance; nucleic acid that contains the sugar deoxyribose


building block (monomer) of nucleic acid polymer

nitrogenous base

a single or double ring of carbon and nitrogen atoms with functional groups


single-ring nitrogenous base


double-ring nitrogenous base

double helix

two strands of nucleotides wound about each other; structure of DNA

DNA replication

process of copying DNA molecules

DNA polymerase

enzyme that makes the covalent bonds between the nucleotides of new DNA strands

ribonucleic acid (RNA)

any nucleic acid containing the sugar ribose


process by which a DNA template is used to produce a single-stranded RNA molecule

messenger RNA

RNA molecule transcribed from a DNA template

RNA polymerase

transcription enzyme that links RNA nucleotides together


internal noncoding region in RNA transcript


coding region in RNA transcript

RNA splicing

process by which the introns are removed from RNA transcripts and the remaining exons are joined together

transfer RNA

RNA that translates the three-letter codons of mRNA to amino acids


in tRNA, a triplet of nitrogenous bases that is complementary to a specific codon in mRNA

ribosomal RNA

RNA component of ribosomes


any change in the nucleotide sequence of DNA


physical or chemical agent that causes mutations

asexual reproduction

process in which a single cell or set of cells produces without sex

sexual reproduction

process in which genetic material from 2 parents combines and produces offspring that differ genetically from either parent


combination of DNA and protein molecules, in the form of long, thin fibers, making up the genetic material in the nucleus of a eukaryotic cell


condensed threads of genetic material formed from chromatin as a cell prepares to divide

sister chromatids

one of a pair of identical chromosomes created before a cell divides


region where 2 sister chromatids are joined tightly together

cell cycle

sequence of events from the production of a eukaryotic cell to the time the cell itself reproduces


stage of the cell cycle during which a cell carries out its metabolic processes an performs its functions in the body

mitotic phase

stage in the cell cycle when a cell is actively dividing


process by which the nucleus and duplicated chromosomes of a cell divide and are evenly distributed, forming 2 daughter nuclei


process by which the cytoplasm of a cell is divided in 2; usually follows mitosis and meiosis


framework of microtubules that guide the movement of chromosomes during mitosis and meiosis


region of cytoplasmic material that in animals cells contain structures called centrioles


first stage of mitosis and of meiosis I and II, when the already replicated chromosomes condense


second stage of mitosis and of meiosis I and II when the spindle is fully formed and all of the chromosomes are held in place


third phase of mitosis and meiosis I and II, in which the sister chromatids separate and move toward the poles of the spindle


final stage of mitosis and of meiosis I and II, in which the chromosomes reach the spindle poles, nuclear envelopes, form around each set of daughter chromosomes, and the nucleoli reappear

cell plate

disk containing cell wall material that develops in plant cells during cytokinesis, eventually dividing the cell into 2 daughter cells

benign tumor

mass of cells that remain at their original site

malignant tumor

mass of abnormal cells resulting from uncontrolled cancer cell division


disease caused by severe disruption of the mechanisms that normally control the cell cycle


spread of cancer cells beyond their original site in the body


type of cell division that produces 4 cells, each with half as many chromosomes as the parent cell


display of a person's 46 chromosomes

homologous chromosomes

one of matching pair of chromosomes, one inherited form each parent

sex chromosome

1 of 2 chromosomes of the 23rd pair of human chromosomes, which determine an individual's gender


having 2 homologous sets of chromosomes and inheriting all chromosomes from parents


diploid cell formed when the nucleus of a haploid sperm cell fuses with the nucleus of a haploid egg cell


having a single set of chromosomes


the fusion of the nuclei and cytoplasm of a haploid sperm cell and a haploid egg cell, forming a diploid zygote


group of 4 chromatids formed during prophase I of meiosis by the 2 sister chromatids in each of the 2 homologous chromosomes

crossing over

exchange of genetic material between homologous chromosomes during prophase I of meiosis

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