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Any change in the structure or function of an organism that allows it to survive and reproduce more effectively in its environment.


Acquired immune deficiency syndrome; a disease caused by the human immunodeficiency virus (HIV).

Alteration of generations

Interchange of asexual and sexual stages of reproduction.


Male sex hormones.


Different size of gametes (small, mobile male and big, motionless and with a lot of resources—female).


(from Greek anthropos—human and genesis—origination)—the process of human origination and formation.


Parthenogenesis in plants.


Parthenogenesis in which only males are produced. Unfertilized eggs of a queen bee produce only males by arrhenotoky.

Artificial selection

Mechanism by which man selects a favorable trait in a population and preserves it through controlled breeding.

Asexual reproduction

Reproduction from a single parent; there is no fusion of nuclei.


Any chromosome other than those determining sex. Autosomes are of the same number and kind in both males and females of a species.



Binary fission

Asexual reproduction in which a one-celled organism divides into two equal parts (by mitosis when a nucleus is present).

Biogenic law

See Recapitulation theory.

Breeds of animals

New forms of animals with economically valuable characters introduced as a result of a selection.


Form of asexual reproduction in which a new individual is produced as an outgrowth of an older one; cell division involving unequal division of the cytoplasm.




Pertaining to the heart and blood vessels.

Central nervous system

The brain and spinal cord.


Any well-marked phenotypic feature that helps to distinguish one species from another. In genetics—any readily defined feature that is transmitted from the parent to the offspring.


Chainlike structures within cell nucleus that contain genes.

Coarctation of the aorta

A narrowing of the aorta, typically found just after the vessels are given off to the left arm.

Coefficient of cefalisation

Relation of brain mass to the body mass.


Present at birth. The term is commonly used in the context of congenital diseases, which are not necessarily genetic in origin.


Type of sexual reproduction found in some one-celled organisms, in which similar gametes from two individuals fuse.

Crossing over

Breaking of linkage groups due to mutual exchange of parts between chromatids of homologous chromosomes during meiosis.


In gymnosperms (cone-bearing plants) and angiosperms (flowering plants), the transfer of pollen from the male reproductive organs to the receptive part of the female reproductive organ on a different plant of the same species.



Depere's laws

1. phylogenetical growth; 2. phylogenetical specialization. Many Vertebrata evolve from small to large forms and from nonspecializing to specializing.


Remarriage after spouse's death.


Organism in which the male and female reproductive structures appear in different individuals.

Dioecious plants

Pistillate flowers are on one plant and staminate flowers—on another. Also called “of two households” plants.


Double set of chromosomes in each cell.

Disruptive selection

A form of natural selection that increases the number of individuals displaying two extremes of a trait, but acts against individuals showing intermediate forms. This gives rise to two distinct groups in the population, showing different phenotypes, and may lead to speciation if selection acts on such traits as breeding season.


Disturbed ability to read.


Deviation of the trait.

Dizygotic (fraternal) twins

Twins that develop from two separate eggs. May be of the same or opposite sex.


Deoxyribonucleic acid, principal component of genes.

Dollo's law—irreversibi-lity of evolution

Evolution is not reversible; i.e., structures or functions discarded during the course of evolution do not reappear in a given line of organisms.

Dominant gene

A gene is said to be dominant if it expresses its phenotype even in the presence of a recessive gene.

Dulong and Petit, Law of

The atomic heat is about the same for the various elements in solid state.



Ebstein’s deformity

The primary abnormality in Ebstein’s Anomaly is of the tricuspid valve, the valve which lies between the right atrium and right ventricle.

Ecological niche

Place that species has in the system of ecological relationships with other organisms and environmental factors.


The science, which deals with the interrelationships between organisms and their physical environment.

Eisenmenger's Complex

Complication of untreated Ventricular Septal Defect. First described by German physician in 1897.


Organism in an early developmental stage.


The study of the embryo’s development.


The sum total of all the conditions and elements, which make up the surroundings and influence the development and actions of an individual.


Estrogen; stimulates development and maintenance of female sex traits.


Female hormones produced by the ovaries.


(from Latin word evolutio—unfolding, development) in biology—irreversible historical development of living nature.


The degree to which a particular genotype is expressed in the phenotype. The degree of expression of a genetically controlled trait.



Fallot’s tetrad

The four abnormalities shown on the right characterize this fairly common condition: 1. There is a ventricular septal defect. 2. There is narrowing of the valve leading to the pulmonary arteries (pulmonic stenosis) 3. The aorta "overrides" the ventricular septal defect. 4. There is thickening (hypertrophy) of the right ventricle.


An individual that produces large usually immobile gametes (as eggs). Bears young. A pistillate plant. Carries Venus sign ♀.


The fusion of dissimilar gametes in sexual reproduction. As a result a zygote is formed.




(from Greek words gamete—wife, gametes—husband)—cell that unites with another cell in sexual reproduction; a sex cell.


Process by which gametes are produced.


The phase in the life cycle of a plant or algae that reproduces sexually, producing gametes. It is usually haploid.


The basic unit of inheritance that controls a characteristic of an organism. Ultramicroscopic area of DNA responsible for transmission of hereditary traits.


Science of heredity.


Organs of reproduction, especially the external organs.


Information contained in the haploid set of chromosomes.


Genetic characteristics inherited by an individual.


The sex glands that produce sex cells.


The sex chromosomes.



Haeckel-Müller’s law)

See Recapitulation theory.

Haploid (monoploid)

Single set of unpaired chromosomes of a given species. Examples are the gametes produced in sexual reproduction and the gametophyte stage of many plants.


A system of sex determination whereby females develop from fertilized eggs and are diploid, while males develop from unfertilized cells and are haploid, as in honeybees.


Genetic transmission of characteristics from parents to their children.


Organism that possesses the sexual organs of both sexes.


1. Chromosome, consisting from heterochromatin. 2. Sex chromosome.

Heterogametic sex

The sex that have double set of autosomes and two different sex chromosomes (XY).


Gametes of different size.


(from Greek geteroiosis—change, transformation). Acceleration of growth, increasing in size, vitality and productivity of first generation hybrids compare to their parents.


Possessing two different alleles of a particular gene on a pair of homologous chromosomes.

Homogametic sex

Sex which has diploid set of autosomes and two X chromosomes.


Sexual preference for member of one's sex.


Possessing identical alleles of a particular gene on a pair of homologous chromosomes.


Chemicals produced by the endocrine glands that regulate growth, development and function of organisms.


Offspring from crossing two different breeds.


Mating or crossing two different breeds (races, forms) of animals or plants.




Mating between closely related individuals (brother—sister, cousins etc.). A population of inbreeding individuals generally shows less genetic variation than an outbreeding population, with many alleles present in the homozygous state.

Intelligence quotient (IQ)

Measurement of “intelligence” expressed as a number or position on a scale. Comparable to term intellectual level.

Internal fertilization

Union of egg and sperm inside the female's body.


Same size of male and female gametes. Both gametes can move. Can be found in many Protozoa.



Libich's law

The plant growth is limited by minimal factor.




An individual that produces small usually mobile gametes (as spermatosoids), which fertilize the eggs. A staminate plant. Carries Mars sign ♂.

Maternal inheritance

A mechanism of inheritance in which certain characteristics of the offspring are determined by the cytoplasm of the egg. The egg contributes far more cytoplasm to the zygote than the male sex cell.


Cell division during which the chromosome number is reduced to monoploid and gametes are produced.


Form of nuclear division characterized by chromosome replication and specific chromosome movements, which maintains the diploid chromosome number in the daughter cells.


Nonhereditary changes of the organism's phenotype under environmental conditions.


1. Flowering plants that have separate female (pistillate) and male (staminate) flowers on the same plant. Also called “of the same household” plants. 2. Other plants and algae that produce male and female gametes on the same individual.
3. Animals that have both male and female reproductive organs on the same individual (see hermaphrodite).


Single marriage; marriage with but one person, husband or wife, at the same time; opposed to polygamy. Also, one marriage only during life; opposed to deuterogamy.


Another name for asexual reproduction.

Monozygotic twins

Identical twins developed from one fertilized egg. Have the same sex.

Multiple-factor hypothesis

A hypothesis that explain quantitative variation by assuming the interaction of a large number of genes (polygenes) each with a small additive effect on the character.


Any agent that initiates or increases the rate of gene mutation in a population.


Change in the composition of a gene, usually causing harmful or abnormal characteristics to appear in the offspring.



Natural selection

Survival of a well-adapted organisms and modification or elimination of less-adapted. The main force of evolution.

Normal distribution

Tendency for most members of a population to cluster around a central point or average with respect to a given trait, with the rest spreading out to the two extremes.




The development of an individual from egg to adult.


See anisogamy.


Process by which egg cells are produced from a female primary sex cell.

Osborn's law

New forms develop in different directions depending on the environmental conditions surrounding them after migration.

Ostium Primum

One of three types of Atrial Septal Defect. Congenital opening in septum near AV valves.

Ostium Secundum

One of three types of Atrial Septal Defect. Congenital defect at the fossa ovalis.


Mating between unrelated or distantly related individuals. A population of outbreeding individuals shows more genetic variation than an inbreeding population and has greater potential for adapting to environmental changes.


Process during which an ovary discharges a mature egg.

Ovum (plural, ova)

Female gamete or germ cell.




The science, which studies the fossils of organisms.


Random mating.


A form of asexual reproduction in which an unfertilized egg develops into a new individual. It is common in lower animals, especially insects

Patent Ductus Arteriosus

Failure after birth of obliteration ductus arteriosus. Leaves communication between aorta and pulmonary artery.


Abnormal physical or mental condition.


The proportion of individuals with a specific genotype who manifest that genotype at the phenotype level.




The observable and measurable characteristics of an organism, a result of the interaction of genotype and environment.


Physical appearance of an organism due to its genotype.


(from Greek phylon—племя, род and genesis—origin)—the evolutionary history or genealogy of a species.


Adaptability to environmental change.


The number of sets of chromosomes in a cell. See haploid, diploid and poliploid.


The small granules, produced in the anther of a flower, in which the male gametes of flowering plants develop.


Transfer of pollen from anther to stigma. See cross-pollination and self-pollination.


One female is mating with several males.


Organism of one sex has several mating partners. See polyandry and polygyny.


See multiple-factor hypothesis.

Polygenic inheritance

Quantitative inheritance. The mechanism of genetic control of traits showing continuous variation.


One male is mating with several females.


An individual with three (triploid), four (tetraploid) or more sets of chromosomes.


(from Latin populus—people) All members of a species inhabiting a given location and therefore are able potentially to mate with each other.


Before birth.

Primary sex ratio

Zygote’s sex ratio after fеrtilization.

Primary sexual characters

Internal and external organs of reproduction (ovaries and testes).




A nonspecific designation of a population of organisms within a species that are geographically, ecologically, physiologically or chromosomally distinct from other members of a species.

Reaction norm

The ability of a genotype to form different phenotypes in ontogeny, depending from environment conditions. Characterizes the influence of an environment in the realization of a trait.

Recapitulation theory

The theory developed by the German biologist Ernst Haeckel (1834-1919) that each organism in its individual embryonic development passes main stages of its predecessors' development—that is, ontogeny tends to recapitulate phylogeny.



Recessive gene

Gene, which is effective only when paired with an identical gene.

Reciprocal hybrids

Direct hybrid is formed from mating a male of breed A with female of breed B. Reciprocal—from male of breed B with female of breed A.


Swapping of DNA between paired chromosomes when eggs and sperm are made.


The process of duplicating or reproducing, as the replication of an exact copy of a polynucleotide strand of DNA or RNA.


The process by which living organisms give rise to new organisms of the same species.

Reproductive system

Set of organs responsible for sexual reproduction.



Secondary sex ratio

Sex ratio at birth.

Secondary sexual characters

An external feature of an organism, not including the reproductive organs themselves, that is indicative of its sex. These characteristics include facial hair in man and breasts in women, combs in cockerels, brightly colored plumage in many male birds and manes in male lions.


(from Latin selectio—selection, choice)—any process that increases or decreases the probability of reproduction. Leads to creation of new forms of plants, animals and microorganisms.


In plants the transfer of pollen from male reproductive organ (anther) to the female reproductive organ (stigma) on the same flower.


Alternative character that distinguish male and female individuals from each other, allows them to produce different gametes and participate in sexual reproduction.

Sex chromosomes

Pair of chromosomes inherited by an individual, which determines sex and certain other characteristics. See Heterogametic sex, Homogametic sex and Sex determination.

Sex determination

The process by which the sex of an organism is determined. In many species, the sex of an individual is dictated by the two sex chromosomes it receives from its parents. In bees and wasps, males are produced from unfertilized eggs and females from fertilized eggs. See Appendix for more details.

Sex linkage

The tendency for some characteristics to occur in one sex.

Sex ratio

Ratio of males to females.

Sexual dimorphism

Differences between male and female sexes.

Sexual reproduction

Any method of reproduction that includes the fusion of the gametes; the fusion is called conjugation when the gametes are similar in structure, and fertilization when they are not.

Sexual selection

A process similar to natural selection but relating exclusively to success in finding a mate for sexual reproduction and producing offspring.


Offspring of the same parents.

Somatic cells

All cells of the body other than gametes (sex cells).


A category of organisms that consist of groups of similar individuals that can interbreed among themselves and produce fertile offspring.


Male gamete.


Meiotic process that produces sperm.


Asexual reproductive sell that can produce another individual.


The internal responses caused by application of a stressor.


Any adjustive demand that requires coping behavior on the part of individual or group.


Species ecologically related to humans (rats, roaches).


Fusion of gametes.


An assemblage of interdependent parts, living or nonliving.



Tertiary sex ratio

Sex ratio of adults in population.


Male reproductive glands or gonads.


Male sex hormone.


Characteristic of individual, which can be observed or measured.

Transposition of the Great Vessels

Aorta and pulmonary arteries are transposed.

Truncus arteriosus

The aorta and pulmonary arteries both arise from a common “trunk”



Variance (σ)

The value of deviation (dispersion) from average value of trait.


A difference between individuals of the same species.



X chromosome

Sex-determining chromosome: all female gametes contain X chromosomes, and if fertilized ovum has also received an X chromosome from its father it will be female.



Y chromosome

Sex-determining chromosome found in half of the total number of male gametes. Y chromosome uniting with X chromosome always provided by female produces a male offspring.




Fertilized egg cell formed by union of male and female gametes.


Revised: 09/30/09.                                                              Back to Home Page        Site Map