Genetics

Heredity

The passing of traits from parents to offspring.

Genetics

The study of heredity and the variation of inherited characteristics.

Deoxyribonucleic Acid (DNA)

A molecule that carries genetic information in cells.

Gene

A segment of a DNA molecule that codes for a particular trait; found at a specific location on a chromosome.

Locus

The location of a gene on a chromosome.

Polyploid

Having more than two sets of chromosomes; many plants are polyploids.

Asexual reproduction

The production of offspring from a single parent; the genetic makeup of the offspring is identical to that of the parent.

Sexual Reproduction

The production of offspring from the fusion of two sex cells (usually from two different parents); the genetic makeup of the offspring is different from that of either parent.

Fragmentation

A method of asexual reproduction in which a piece or body fragment of the parent organism develops into a mature individual.

Mitosis

The process by which a eukaryotic cell divides the genetic material in its nucleus into two new identical nuclei.

Interphase

The portion of the cell cycle between mitotic divisions when the genetic material (in the form of chromatin) is duplicated.

Chromatin

The tangled strands of DNA and protein within a eukaryotic nucleus.

Sister chromatid

The identical copy of a single chromosome that remains attached to the original chromosome at the centromere.

Cytokinesis

The process in which a eukaryotic cell divides its cytoplasm into two new daughter cells.

Cloning

The process of producing one individual that is genetically identical to another, using a single cell or tissue.

Biotechnology

The use and modification of organisms for applications in engineering, industry, and medicine.

Genetically Modified Organism

An organism in which the genetic material has been altered using genetic engineering techniques.

Gamete

A sex cell; includes sperm cells in males and egg cells in females.

Fertilization

The formation of a zygote by the joining together, or fusion, of two gametes.

Zygote

A cell produced by the fusion of two gametes.

Meiosis

A two-stage cell division in which the resulting daughter cells have half the number of chromosomes as the parent cell; results in the formation of gametes or spores.

Homologous Chromosomes

Matching pairs of chromosomes, similar in size and carrying information for the same genes.

Tetrad

A pair of homologous chromosomes, each with two sister chromatids.

Synapsis

The physical pairing up of homologous chromosomes during prophase I of meiosis.

Crossing Over

The exchange of chromosome segments between homologous pairs during synapsis.

Gametogenesis

The production of gametes (sex cells) in animals.

Spermatogenesis

The production of mature sperm cells.

Oogenesis

The production of mature egg cells.

Karyotype

The chromosomes of an individual that have been sorted and arranged according to size and type.

Sex Chromosomes

Chromosomes that differ in males and females of the same species; the combination of sex chromosomes determines the sex of the offspring.

Autosomes

Non-sex chromosomes.

Non-disjunction

The failure of homologous chromosomes to move to opposite poles of the cell during meiosis; results in an abnormal number of chromosomes in the daughter cells.

Trisomy

A chromosomal abnormality in which there are three homologous chromosomes in place of a homologous pair.

Monosomy

A chromosomal abnormality in which there is a single chromosome in place of a homologous pair.

Down syndrome

A chromosomal abnormality in which an individual has three copies of chromosome number 21; also referred to as trisomy 21.

Prenatal Testing

Testing for a genetic disorder that occurs prior to birth.

Turner syndrome

One X and no Y sex chromosome, resulting in females that do not mature sexually and are sterile.

Klinefelter syndrome

Two X and one Y sex chromosome, resulting in males who are usually sterile and exhibit some feminine body characteristics.

Patau syndrome

Trisomy of chromosome 13, associated with serious developmental problems.

Edwards syndrome

Trisomy of chromosome 18, which often results in organ system defects and very low survival rates.

Maternal Inheritance

A type of inheritance in which a zygote formed from two gametes inherits cytoplasmic DNA from only the female gamete.

Paternal Inheritance

A type of inheritance in which a zygote formed from two gametes inherits cytoplasmic DNA from only the male gamete.

Horizontal Gene Transfer

The transfer of genetic information from one species into a different species.

ENDOSYMBIOTIC THEORY

The theory that mitochondria and chloroplasts in eukaryotic cells were once aerobic bacteria that were ingested by a large anaerobic bacterium.

Trait

A particular version of a characteristic that is inherited, such as hair color or blood type.

True-Breeding Organism

An organism that produces offspring that are genetically identical for one or more traits when self-pollinated.

Hybrid

The offspring of two different true-breeding plants.

P Generation

The parent plants used in a cross.

F1 Generation

The offspring of a P-generation cross.

Monohybrid

The offspring of two different true-breeding plants that differ in only one characteristic.

Monohybrid Cross

A cross designed to study the inheritance of only one trait.

F2 Generation

The offspring of an F1 generation cross.

Law of Segregation

A scientific law stating that organisms inherit two copies of genes, one from each parent.

Allele

A specific form of a gene.

Homozygous

Describes an individual that carries two identical alleles for a given characteristic.

Heterozygous

Describes an individual that carries two different alleles for a given characteristic.

Genotype

The genetic makeup of an individual.

Phenotype

An individual's outward appearance with respect to a specific characteristic.

Dominant Allele

The allele that, if present, is always expressed.

Recessive Allele

The allele that is expressed only if the dominant allele is not present.

Punnett Squares

A diagram that summarizes every possible combination of each allele from each parent.

Probability

The likelihood that an outcome will occur if it is a matter of chance.

Test Cross

A cross used to determine the genotype of an individual expressing a dominant trait.

Complete Dominance

A situation where an allele will determine the phenotype, regardless of the presence of another allele.

Incomplete Dominance

A situation where neither allele dominates the other and both have an influence on the individual.

Codominance

A situation where both alleles are expressed fully to produce offspring with a third phenotype.

Pedigree

A diagram of an individual's ancestors used to analyze the Mendelian inheritance of a certain trait.

Autosomal Inheritance

Inheritance of alleles located on non-sex chromosomes.

Sex-Linked

Describes an allele found on one of the sex chromosomes.

X-linked

Phenotypic expression of an allele that is found on the X chromosome.

Y-linked

Phenotypic expression of an allele that is found on the Y chromosome.

Dihybrid Cross

A cross that involves two genes, each consisting of heterozygous alleles.

Law of Independent Assortment

If genes are located on separate chromosomes, they will be inherited independently of one another.

Product Law

The probability of two independent random events both occurring is the product of the individual probabilities.

Continuous Variation

When the product of one gene is affected by the product of another gene, resulting in an additive or negated effect.

Additive Allele

An allele that has a partial influence on a phenotype.

Nuclein

The original name given to DNA when it was discovered in the nucleus of cells.

Nucleotide

The repeating unit in DNA that comprises a deoxyribose sugar, a phosphate group, and one of four nitrogenous bases.

X-ray crystallography

A technique used to reveal the structure of a pure substance by observing the pattern of X-rays.

Scientific Model

A simplified representation of a concept that can be tangible or conceptual.

Complementary Base Pairing

Pairing of nitrogenous bases of one DNA strand with another; A with T, and G with C.

Point Mutation

A small-scale change in the nitrogenous base sequence of a DNA.

Chromosome Mutation

An error that involves an entire chromosome or a large part of a chromosome.

Spontaneous Mutation

A mutation that occurs randomly, not caused by any outside factors.

Induced Mutation

A mutation that occurs due to exposure to an outside factor.

Antibiotic Resistance

Describes strains of bacteria that are no longer susceptible to the effects of antibiotics.

Transposons

Sequences of DNA that can move along and between chromosomes, potentially causing changes in an organism's phenotype.

Restriction Enzymes

Molecules that can cut DNA at specific sites.

Recombinant DNA

A DNA fragment consisting of nucleotide sequences from at least two different sources.