Biology 30 Diploma key terms

One of the alternative versions of a gene that can occupy a given position on a chromosome; different alleles may produce different traits or no observable difference at all.

A segment of DNA that carries the instructions for building a functional product, usually a protein, and is passed from parents to offspring during reproduction.

The particular combination of alleles an organism carries for one or more genes, written as letters such as AA, Aa, or aa.

The observable characteristics of an organism, such as eye colour or blood type, produced by the interaction of its genotype with the environment.

An allele that produces its trait even when only one copy is present, masking the effect of a recessive allele paired with it in a heterozygote.

An allele whose trait appears only when two copies are present, because its effect is hidden whenever a dominant allele is also inherited.

Describes an organism carrying two identical alleles for a particular gene, such as two dominant alleles or two recessive alleles.

Describes an organism carrying two different alleles for a particular gene, one inherited from each parent, often written with one capital and one lowercase letter.

A grid used to predict the possible genotypes of offspring by combining the gametes each parent can produce for a chosen trait or set of traits.

A breeding experiment that follows the inheritance of a single trait controlled by one gene, typically starting with true-breeding parents that differ in that trait.

A breeding experiment that tracks two different traits at the same time, used to test whether the genes for those traits assort independently.

A cross between an individual showing a dominant trait and a homozygous recessive individual, performed to reveal whether the unknown individual is homozygous or heterozygous.

A pattern in which the heterozygote shows a blended intermediate phenotype rather than either parental trait, as when red and white flowers produce pink offspring.

A pattern in which both alleles are fully expressed in the heterozygote, so the phenotype shows both traits at once, as in AB human blood type.

The situation in which a gene has more than two possible alleles within a population, although any one individual still carries only two.

A trait whose gene is located on a sex chromosome, most often the X chromosome, causing inheritance patterns that differ between males and females.

An individual who carries one copy of a recessive allele but does not show the trait, yet can pass that allele to offspring.

A family tree diagram using symbols and shading to trace how a trait or disorder is inherited across several generations.

A photograph-style display of an individual's chromosomes arranged in pairs by size and shape, used to detect extra, missing, or altered chromosomes.

The failure of homologous chromosomes or sister chromatids to separate properly during meiosis, producing gametes with too many or too few chromosomes.

A type of cell division that halves the chromosome number and produces four genetically varied haploid cells, which become gametes in animals.

The exchange of corresponding segments between homologous chromosomes during prophase I of meiosis, creating new combinations of alleles on a chromosome.

The random arrangement and separation of different homologous pairs during meiosis, so alleles of different genes are distributed into gametes independently of one another.

A permanent change in the DNA sequence of a gene or chromosome, which may be harmful, neutral, or occasionally beneficial and is the ultimate source of new alleles.

The maintenance of a relatively stable internal environment within narrow limits despite changes outside the body, achieved through feedback mechanisms.

A control mechanism in which a change in a variable triggers a response that counteracts or reverses that change, returning the body toward its set point.

A control mechanism in which a change in a variable triggers a response that amplifies that change, pushing the system further from its starting state.

A chemical messenger secreted by an endocrine gland or cell that travels in the blood and alters the activity of specific target cells bearing matching receptors.

A cell that responds to a particular hormone because it carries receptor molecules shaped to bind that hormone specifically.

A protein molecule, often on a cell membrane or inside a cell, that binds a specific signalling molecule and triggers a response in that cell.

A specialized nerve cell that receives, integrates, and transmits electrical and chemical signals throughout the nervous system.

A rapid, self-propagating change in the electrical charge across a neuron's membrane, produced by ion movements and used to carry signals along an axon.

A chemical released from the end of a neuron that crosses a synapse and binds receptors on the next cell, passing the signal onward or altering its activity.

The small gap between two neurons, or between a neuron and a muscle or gland cell, across which chemical signals pass.

A Y-shaped protein produced by certain white blood cells that binds specifically to a foreign molecule, helping to neutralize or mark it for destruction.

Any molecule, often on the surface of a pathogen or foreign cell, that the immune system recognizes as non-self and can trigger a specific immune response.

The coordinated series of actions by which the body recognizes and defends against foreign invaders or abnormal cells, involving many types of white blood cells.

A preparation containing weakened, inactivated, or partial pathogen material that stimulates an immune response and creates memory without causing serious disease.

A growth response in which a plant bends toward or away from a light source because of unequal cell elongation on opposite sides of the stem.

A plant hormone, mainly indoleacetic acid, that promotes cell elongation and is redistributed in response to light or gravity to direct growth.