Key Terms in Genetics and Evolution

heredity

The passing of traits from parents to offspring.

true-breeding

Organisms that, when mated, produce offspring identical to themselves.

P generation

The parental generation in a genetic cross.

F1 generation

The first generation of offspring from a genetic cross.

F2 generation

The second generation of offspring from a genetic cross.

dominant

An allele that expresses its phenotype even in the presence of a recessive allele.

recessive

An allele that only expresses its phenotype in the absence of a dominant allele.

genes

Units of heredity that contribute to an organism's traits.

homozygous

An organism with two identical alleles for a trait.

heterozygous

An organism with two different alleles for a trait.

allele

Different forms of a gene that can exist at a specific locus.

phenotype

The observable physical or biochemical characteristics of an organism.

genotype

The genetic constitution of an organism.

Punnett square

A diagram used to predict the outcome of a genetic cross.

probability

The likelihood of a particular genetic outcome occurring.

testcross

A cross between an individual with an unknown genotype and a homozygous recessive individual.

law of segregation

The principle that alleles for a trait separate during gamete formation.

dihybrid

An organism that is heterozygous for two traits.

law of independent assortment

The principle that genes for different traits segregate independently of one another.

polygenic

A trait controlled by multiple genes.

continuous variation

Variation in a trait that occurs over a range rather than in discrete categories.

pleiotropic

A gene that influences multiple phenotypic traits.

incomplete dominance

A genetic situation in which one allele does not completely dominate another allele.

epistasis

A form of gene interaction in which one gene masks the effects of another gene.

modified ratio

A ratio that is altered due to interactions between alleles.

codominant

A situation in which both alleles in a heterozygote are fully expressed.

ABO blood groups

The classification of human blood based on the presence or absence of antigens.

sex-linked

Traits associated with genes located on sex chromosomes.

linkage

The tendency of genes located close together on a chromosome to be inherited together.

autosomes

Chromosomes that are not sex chromosomes.

sex chromosomes

Chromosomes that determine the sex of an individual.

nondisjunction

The failure of homologous chromosomes to separate properly during cell division.

aneuploidy

An abnormal number of chromosomes in a cell.

monosomics

Organisms with one less chromosome than the normal diploid number.

trisomics

Organisms with one extra chromosome than the normal diploid number.

Down syndrome

A genetic disorder caused by the presence of an extra chromosome 21.

pedigree

A diagram that shows the occurrence of a genetic trait in several generations of a family.

albinism

A genetic condition characterized by a lack of melanin pigment.

color blindness

A genetic disorder in which an individual cannot distinguish certain colors.

hemophilia

A genetic disorder that impairs the body's ability to make blood clots.

sickle-cell disease

A genetic disorder that affects hemoglobin and causes red blood cells to become misshapen.

Tay-Sachs disease

A genetic disorder that results in the destruction of nerve cells in the brain and spinal cord.

Huntington's disease

A genetic disorder that causes the progressive breakdown of nerve cells in the brain.

genetic counseling

A process to help individuals understand genetic conditions and risks.

amniocentesis

A medical procedure used to obtain a sample of amniotic fluid for genetic testing.

ultrasound

A medical imaging technique used to visualize internal structures.

chorionic villus sampling

A prenatal test that involves taking a sample of tissue from the placenta.

preimplantation genetic screening

A procedure used to identify genetic defects in embryos before implantation.

proteins

Large biomolecules made up of amino acids that perform various functions in the body.

DNA

The molecule that carries the genetic instructions for life.

nucleotides

The building blocks of DNA and RNA, consisting of a sugar, a phosphate group, and a nitrogenous base.

purines

A type of nitrogenous base in DNA and RNA, including adenine and guanine.

pyrimidines

A type of nitrogenous base in DNA and RNA, including cytosine, thymine, and uracil.

Chargaff's rule

The principle that in DNA, the amount of adenine equals thymine and the amount of guanine equals cytosine.

helix

A spiral structure formed by a chain of molecules.

double helix

The structure of DNA, consisting of two intertwined strands.

base pairs

Pairs of nitrogenous bases that connect the complementary strands of DNA.

complementarity

The principle that specific bases pair with each other in DNA and RNA.

DNA replication

The process by which DNA makes a copy of itself.

DNA repair

The mechanisms by which a cell identifies and corrects damage to its DNA.

mutation

A change in the DNA sequence that can lead to changes in phenotype.

recombination

The process by which genetic material is physically mixed during meiosis.

DNA fingerprinting

A technique used to identify individuals based on unique patterns in their DNA.

point mutation

A mutation that involves a change in a single nucleotide.

frame-shift mutation

A mutation that results from the insertion or deletion of nucleotides, altering the reading frame.

mutagen

An agent that causes genetic mutation.

transposition

The movement of a DNA sequence from one location to another within the genome.

chromosomal rearrangement

A change in the structure of a chromosome.

DNA→ RNA→ protein

The central dogma of molecular biology describing the flow of genetic information.

gene expression

The process by which information from a gene is used to synthesize a functional gene product.

transcription

The process of copying a segment of DNA into RNA.

messenger RNA (mRNA)

The RNA molecule that carries genetic information from DNA to the ribosome.

RNA polymerase

The enzyme that synthesizes RNA from a DNA template.

genes

Segments of DNA that code for proteins or functional RNA.

translation

The process by which ribosomes synthesize proteins using mRNA as a template.

genetic code

The set of rules by which information encoded in genetic material is translated into proteins.

codon

A sequence of three nucleotides that corresponds to a specific amino acid.

ribosome

The cellular structure that synthesizes proteins by translating mRNA.

ribosomal RNA (rRNA)

The RNA component of ribosomes, essential for protein synthesis.

transfer RNA (tRNA)

The type of RNA that carries amino acids to the ribosome during protein synthesis.

anticodon

A sequence of three bases on tRNA that is complementary to a codon on mRNA.

exon

A segment of a gene that is expressed and codes for a protein.

intron

A non-coding segment of a gene that is removed during RNA processing.

primary RNA transcript

The initial RNA molecule synthesized from a DNA template before processing.

alternative splicing

The process by which different combinations of exons are joined together to produce multiple proteins from a single gene.

promoter

A DNA sequence that initiates transcription of a particular gene.

repressor

A protein that inhibits gene transcription.

activator

A protein that increases gene transcription.

operon

A cluster of genes under the control of a single promoter.

epigenetic modification

Changes in gene expression that do not involve alterations to the DNA sequence.

basal transcription factors

Proteins that are essential for the transcription of all protein-coding genes.

specific transcription factors

Proteins that regulate the transcription of specific genes.

enhancer

A DNA sequence that increases the likelihood of transcription of a particular gene.

coactivators

Proteins that assist transcription factors in increasing gene expression.

mediators

Proteins that act as intermediaries between transcription factors and RNA polymerase.

gene silencing

The process by which a gene's expression is inhibited.

RNA interference

A biological process in which RNA molecules inhibit gene expression.

binary fission

A method of asexual reproduction in which a single organism divides into two identical organisms.

species

A group of organisms that can interbreed and produce fertile offspring.

Galápagos Islands

An archipelago known for its unique species and contributions to the theory of evolution.