AP Bio Vocab #3

Gene

A discrete unit of hereditary information consisting of a specific nucleotide sequence in DNA (or RNA, in some viruses).

Asexual Reproduction

The generation of offspring from a single parent that occurs without the fusion of gametes (by budding, division of a single cell, or division of the entire organism into two or more parts). In most cases, the offspring are genetically identical to the parent.

Clone

A lineage of genetically identical individuals or cells.

Sexual Reproduction

A type of reproduction in which two parents give rise to offspring that have unique combinations of genes inherited from both parents via the gametes.

Karyotype

A display of the chromosome pairs of a cell arranged by size and shape.

Homologous Chromosomes

A pair of chromosomes of the same length, centromere position, and staining pattern that possess genes for the same characters at corresponding loci. One homologous chromosome is inherited from the organism's father, the other from the mother. Also called homologs, or a homologous pair.

Sex Chromosomes

A chromosome responsible for determining the sex of an individual.

Autosome

A chromosome that is not directly involved in determining sex; not a sex chromosome.

Haploid Cell

A cell containing only one set of chromosomes (n).

Fertilization

The union of haploid gametes to produce a diploid zygote.

Gamete

A haploid reproductive cell, such as an egg or sperm. They unite during sexual reproduction to produce a diploid zygote.

Zygote

The diploid product of the union of haploid gametes during fertilization; a fertilized egg.

Diploid Cell

A cell containing two sets of chromosomes (2n), one set inherited from each parent.

Meiosis

A modified type of cell division in sexually reproducing organisms consisting of two rounds of cell division but only one round of DNA replication. It results in cells with half the number of chromosome sets as the original cell.

Crossing Over

The reciprocal exchange of genetic material between nonsister chromatids during prophase I of meiosis.

Trait

One of two or more detectable variants in a genetic character.

True-breeding

Referring to organisms that produce offspring of the same variety over many generations of self-pollination.

P Generation

The true-breeding (homozygous) parent individuals from which F1 hybrid offspring are derived in studies of inheritance; P stands for "parental."

F1 Generation

The first filial, hybrid (heterozygous) offspring arising from a parental (P generation) cross.

F2 Generation

The offspring resulting from interbreeding (or self-pollination) of the hybrid F1 generation.

Allele

Any of the alternative versions of a gene that may produce distinguishable phenotypic effects.

Dominant

An allele that is fully expressed in the phenotype of a heterozygote.

Recessive

An allele whose phenotypic effect is not observed in a heterozygote.

Law of Segregation

Mendel's first law, stating that the two alleles in a pair segregate (separate from each other) into different gametes during gamete formation.

Homozygous

Having two identical alleles for a given gene.

Heterozygous

Having two different alleles for a given gene.

Phenotype

The observable physical and physiological traits of an organism, which are determined by its genetic makeup.

Genotype

The genetic makeup, or set of alleles, of an organism.

Testcross

Breeding an organism of unknown genotype with a homozygous recessive individual to determine the unknown genotype. The ratio of phenotypes in the offspring reveals the unknown genotype.

Monohybrid

An organism that is heterozygous with respect to a single gene of interest. All the offspring from a cross between parents homozygous for different alleles are monohybrids. For example, parents of genotypes AA and aa produce a monohybrid of genotype Aa.

Dihybrid

An organism that is heterozygous with respect to two genes of interest. All the offspring from a cross between parents doubly homozygous for different alleles are dihybrids. For example, parents of genotypes AABB and aabb produce a dihybrid of genotype AaBb.

Law of Independent Assortment

Mendel's second law, stating that each pair of alleles segregates, or assorts, independently of each other pair during gamete formation; applies when genes for two characters are located on different pairs of homologous chromosomes or when they are far enough apart on the same chromosome to behave as though they are on different chromosomes.

Incomplete Dominance

The situation in which the phenotype of heterozygotes is intermediate between the phenotypes of individuals homozygous for either allele.

Codominance

The situation in which the phenotypes of both alleles are exhibited in the heterozygote because both alleles affect the phenotype in separate, distinguishable ways.

Polygenic Inheritance

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

Pedigree

A diagram of a family tree with conventional symbols, showing the occurrence of heritable characters in parents and offspring over multiple generations.

Carrier

In genetics, an individual who is heterozygous at a given genetic locus for a recessively inherited disorder. The heterozygote is generally phenotypically normal for the disorder but can pass on the recessive allele to offspring.

Phenotypic Plasticity

The ability of one genotype to produce more than one phenotype when exposed to different environments, as the modification of developmental events by the environment, or as the ability of an individual organism to alter its phenotype in response to changes in environmental conditions.

Semiconservative Replication (Model)

Type of DNA replication in which the replicated double helix consists of one old strand, derived from the parental molecule, and one newly made strand.

Transcription

The synthesis of RNA using a DNA template.

Translation

The synthesis of a polypeptide using the genetic information encoded in an mRNA molecule. There is a change of "language" from nucleotides to amino acids.

Gene Expression

The process by which information encoded in DNA directs the synthesis of proteins or, in some cases, RNAs that are not translated into proteins and instead function as RNAs.

Operon

A unit of genetic function found in bacteria and phages, consisting of a promoter, an operator, and a coordinately regulated cluster of genes whose products function in a common pathway.

Transcription Factor

A regulatory protein that binds to DNA and affects transcription of specific genes.

Epigenetic Inheritance

Inheritance of traits transmitted by mechanisms not directly involving the nucleotide sequence of a genome.

Induction

The process in which one group of embryonic cells influences the development of another, usually by causing changes in gene expression.

Differentiation

The process by which a cell or group of cells become specialized in structure and function.

Mutation

A change in the nucleotide sequence of an organism's DNA or in the DNA or RNA of a virus.

Plasmid

A small, circular, double-stranded DNA molecule that carries accessory genes separate from those of a bacterial chromosome; in DNA cloning, used as vectors carrying up to about 10,000 base pairs (10 kb) of DNA. They are also found in some eukaryotes, such as yeasts.

Recombinant DNA

A DNA molecule made in vitro with segments from different sources.

Restriction Enzyme

An endonuclease (type of enzyme) that recognizes and cuts DNA molecules foreign to a bacterium (such as phage genomes). The enzyme cuts at specific nucleotide sequences (restriction sites).

Restriction Site

A specific sequence on a DNA strand that is recognized and cut by a restriction enzyme.

Restriction Fragment

A DNA segment that results from the cutting of DNA by a restriction enzyme.

Gel Electrophoresis

A technique for separating nucleic acids or proteins on the basis of their size and electrical charge, both of which affect their rate of movement through an electric field in a gel made of agarose or another polymer.

Capsid

The protein shell that encloses a viral genome. It may be rod-shaped, polyhedral, or more complex in shape.

Reverse Transcriptase

An enzyme encoded by certain viruses (retroviruses) that uses RNA as a template for DNA synthesis.

Lytic Cycle

A type of phage replicative cycle resulting in the release of new phages by lysis (and death) of the host cell.

Lysogenic Cycle

A type of phage replicative cycle in which the viral genome becomes incorporated into the bacterial host chromosome as a prophage, is replicated along with the chromosome, and does not kill the host.

Conjugation

In prokaryotes, the direct transfer of DNA between two cells that are temporarily joined. When the two cells are members of different species, it results in horizontal gene transfer.

Transformation

A change in genotype and phenotype due to the assimilation of external DNA by a cell. When the external DNA is from a member of a different species, this results in horizontal gene transfer.

Transduction

A process in which phages (viruses) carry bacterial DNA from one bacterial cell to another. When these two cells are members of different species, it results in horizontal gene transfer.