Glossary

Glossary:

A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z |

~ A ~

Allele - One of the two or more alternative forms of a gene occupying the same locus on a particular chromosome or linkage structure and differing from other alleles at the locus at one or more mutational sites.

Angiosperm - A plant whose seeds are borne within an ovary (fruit).

Annual - A plant in which the entire life cycle is completed in a single growing season.

Anther - The pollen-bearing portion of the stamen.

~ B ~

Breed true - To produce a self-pollinated plant whose offspring are identical to itself (see segregation).

Bud - An underdeveloped shoot.

~ C ~

Cell - The structural and functional unit of living organisms. A "living entity" unto itself.

Cell wall - The rigid outermost layer of a plant cell.

Chromosome - A long, threadlike association of genes in the nucleus of all eukaryotic cells, consisting of DNA and proteins.

Cotyledon - A primary leaf; generally stores food in dicotyledons and absorbs food in monocotyledons.

Cross- pollination - The transfer of pollen from the anther of one plant to the stigma of another.

Cytoplasm - The protoplasm of a cell excluding the nucleus.

~ D ~

Dehiscence - The opening of an anther, fruit, or other structure to permit the escape of reproductive bodies.

Dicotyledon - A plant whose embryo has two cotyledons; a dicot.

Diffusion - The movement of a substance from an area of high concentration to an area of lesser concentration as a result of random movement.

Diploid - Having two sets of chromosomes (2n), one inherited from each parent, where (n) represents the number of chromosomes.

Dominance - Refers to the expression of genetically controlled characters (phenotypes) and their corresponding alleles when they are in the heterozygous condition.

Dominant - A gene that exerts its full phenotypic effect regardless of its allelic partner, thus masking the partner's effects.

Dominant allele - In a heterozygote, the allele that is fully expressed in the phenotype.

~ E ~

Eukaryotic - Having cells with a membrane-bound nucleus, membrane-bound organelles, and chromosomes in which DNA is associated with proteins.

~ F ~

F₁ Generation - The offspring produced by crossing two true-breeding plants; the first filial generation.

Fertilization - The union of an egg (n) with a sperm (n) to form a zygote (2n).

Flower - The reproductive structure of an angiosperm.

Fruit - The mature, ripened ovary containing the seeds of an angiosperm.

~ G ~

Gamete - A mature, functional haploid cell whose nucleus fuses with that of another gamete of the opposite sex to form a zygote.

Gametophyte - A gamete producing plant.

Gene - A sequence of nucleotides along a molecule of DNA that makes up a unit of inheritance.

Genotype - The genetic makeup of an organism.

Germination - The beginning of growth by a seed.

~ H ~

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

Heterozygous - Having two different alleles for a given trait.

Homozygous - Having two identical alleles for a given trait.

Hybrid - A plant resulting from a cross between two pure-breeding lines.

~ I ~

Incomplete Dominance - The condition that results when two different alleles together produce an effect intermediate between the effects of the same two genes in a homozygous condition.

Independent Assortment - The normally random distribution of alleles during meiosis.

Integument - The outermost layer of tissue enveloping the nucleus of the ovule; develops into the seed coat.

~ L ~

Locus - The position of a gene on a genetic map. Allelic gene are situated at identical loci in homologous chromosomes.

~ M ~

Meiosis - The reduction of chromosome number from diploid to haploid in which segregation of genes occurs and gametes or spores are formed.

Mitosis - The segregation of duplicated chromosomes in a cell nucleus preceding cell division.

Mutant - Any heritable variation from the wild type that is the result of a mutation. Often (but not always) recessive.

~ N ~

Natural Selection - A process that occurs in nature whereby strong and well-adapted organisms survive while weak and poorly adapted organisms eventually die out.

~ O ~

Ovary - The enlarged basal portion of the pistil housing the ovules.

Ovule - A structure in a seed plant containing the female gametophyte with egg cell and surrounded by one or two integuments.

~ P ~

Phenotype - The physical and physiological traits of an organism.

Pigment - Substance that absorbs light, often selectively.

Pollen - A collective term for pollen grains.

Pollination - The transfer of pollen from the anther to the stigma.

~ R ~

Recessive - A gene whose phenotypic expression is masked by its dominant allele.

~ S ~

Segregation - In genetics, the separation of allele pairs from one another and their distribution to different cells observed only in heterozygous genotypes.

Self Pollination - The transfer of pollen from the anther of a flower to the stigma of the same flower or of another flower on the same plant.

Species - Usually, the smallest unit of classification; includes individuals which can breed with each other, produce viable offspring, have the same chromosome number, and share a common gene pool.

Stamen - The part of the flower producing pollen, composed of an anther and filament.

Stigma - The receptive surface of the pistil to which pollen grains adhere and on which they germinate.

~ T ~

Test Cross - A cross of a dominant with homozygous recessive; used to determine whether the dominant is homozygous or heterozygous. If two or more genes are involved, the test cross is used to determine the linkage relationship between the different genes.

~ V ~

Variation - The differences that occur within the offspring of a particular species.

Variegated - A plant with yellow or white blotches or streaks on the green leaves and stems, as well as on flower buds and flowers.

~ W ~

Wild Type - The phenotype that is predominant in the majority of individuals of a species in the natural environment, chosen to be the standard for comparing other phenotypes.

~ Z ~

Zygote - The diploid (2n) cell resulting from the union of the male and female gametes.