Heredity

BIBLIOGRAPHY

From a historical and biological perspective, heredity is the transfer of traits from a parent organism to its offspring. Traditional conceptualizations of heredity have focused on genes and the expression of genetic code that is transferred during reproduction. More recently and in response to knowledge about the limits of genetics in the human phenotypes and behavior, the conceptualization of heredity has been expanded to include the transfer of characteristics of the parent organism to offspring via a range of mechanisms, to include social institutions.

First described as animalcules and ultimately the basis of the school of scientists known as “spermists,” early thinkers such as Anton van Leeuwenhoek recognized that there were microscopic parts of the human existence. Others went further to suggest that sperm contained little men who were small representations of adults. As such, heredity was determined by the male of the species, and the role of women in reproduction was simply to carry the homunculus that had been deposited by the male. As a reflection of societal values and the diminished value of women, this theory of heredity prevailed throughout the seventeenth century.

In a controversial and radical move forward, Gregor Mendel was credited for determining the rules associated with genetic transfer in the 1800s in a series of experiments using garden peas. He established patterns of inheritance by observing frequency of traits such as seed color and based on assumptions that the frequency was a direct function of specified patterns of genetic transmission. It was he who observed patterns and coined subsequent rules of genetics, notably the basis of modern genomic theories.

During this era science recognized that both the male and female contributed to heredity and that the ovum and sperm fused toward the development of a synergistic being. The mechanism of this transmission was later determined to be deoxyribonucleic acid (DNA), which was carried on chromosomes. From these seminal discoveries emerged the notion of the “central dogma” that indicates that DNA codes for ribonucleic acid (RNA) in transcription and RNA codes for proteins through a translational process. DNA was ultimately recognized as the blueprint in the direction of cellular activities, tissue and organ functions, and organismic activity and reproduction in both plants and animals.

The molecular structure of DNA was deduced in 1953 by James Watson and Francis Crick and has since served as the basis for understanding modern molecular and behavioral genetics. DNA is characterized as a polymeric double helix containing repeating nucleotide bases linked to phosphorylated sugars. These DNA molecules are arranged in linear or circular chromosomes, specific to species. In some organisms, chromosomes are circular and singular, but in most higher order organisms, chromosomes exist in linear and duplicate form. For example, humans have twenty-three pairs of chromosomes, where inheritance is derived from both mother and father. The sequence of repeating units that make up DNA determines the organism’s genotype and, ultimately, phenotype. Genetic variation occurs when there is a change in the DNA sequence secondary to biological or environmental provocation.

We have grown to recognize that heredity significantly influences how we look and how we behave in, anticipate, and respond to our environmental context. This includes how and what we contract in terms of disease, how disease susceptibility is manifest in subsequent generations, and how wellness is defined. In a reciprocal fashion, our environmental context modifies the relationship between genotype and phenotype. Genotype influences phenotype but may produce several different phenotypes, depending on the environmental context. One example is phenylketonuria. This disease is caused by a genetic defect that results in a buildup of phenylalanine, which causes brain damage in children. However, if the affected child’s diet contains low levels of phenylalanine, mental retardation is prevented. This environmental change prevents disease presentation, even though the genotype would otherwise predict disease and mental retardation.

Inheritance in humans is often difficult to study. First, all study methods outside the laboratory are observational; scientific ethics prevent us from forcing or selectively controlling mating in humans. Secondly, it is very difficult to study human heredity prospectively because we have very long generation times. As a consequence, a number of techniques have been discovered that uniquely and creatively provide insight into the human inheritance. These include the use of pedigree, twin, and adoption studies. Pedigree studies give scientists a long-term picture of the inheritance of a given trait, or of several traits, by several generations of a given family. Specific rules regarding pedigrees allow researchers to determine the pattern of inheritance, such as whether a trait is autosomal dominant, autosomal recessive, X-linked dominant, X-linked recessive, or Y-linked. Dizygotic and monozygotic twins offer insight into the influence of environment on diseases with a significant genetic etiology. Since monozygotic twins share the same genetic makeup, it is expected that the manifestation of a genetic trait would be the same for the pair if they are in the same environment. Low concordance in monozygotic twins signals to investigators that environmental factors play a large role in the characteristic. Similarly, but from an environmental perspective, adoption studies also assist with determining the influence of environment and genetics on human functioning. Persons who are adopted often have few genes in common with their parents. However, they share the same environment for a number of years and often have health characteristics similar to those of their adoptive parents. Comparisons are made between adoptees and their adoptive parents, as well as between adoptees and one or both natural parents.

Inheritance is also of interest to those who study human behavior. For example, because of advances in statistical procedures and the use of twin methodologies in recent years, several researchers have begun evaluating the genetic influence of common psychiatric and personality traits, coping, and other behaviors. For example, using behavioral and molecular genetic analyses, Whitfield et al. (2006) recently reported that up to 35 percent of the variance in coping may be genetically mediated. This study suggests that genetics may provide a baseline for coping that is ultimately malleable and susceptible to learning and environmental influences. Similarly, Whitfield et al (2007) reported that 60 percent of individual smoking behavior was genetically mediated, with very few meaningful differences in the genes that determine or influence smoking behavior between racially classified social groups.

Studies like those reported above have been used by some to promote biological explanations for social phenomena and suggest genetic predispositions for favorable or unfavorable social outcomes. Notably, the prevailing scientific evidence strongly challenges genetic explanations in the etiology of social outcomes and suggests that societal inequities are much more salient than are genetic factors.

The recent growth of genomics as a science has frequently exceeded our planning and thinking on topics such as ethics, morals, and the law. Our physical capacity to disentangle the building blocks of human existence has not always been equaled by our appreciation for the impact of such knowledge. For example, should predispositions identified by genetic testing be reported to insurance companies as an acceptable factor in the calculation of risk and an influence on the cost of insurance premiums? Should our ability to manipulate phenotypic characteristic in humans (blond hair, blue eyes, tall, etc.) be used in a fashion representative of a modern-day extension of the concept of eugenics put forth by Francis Galton in the mid-1800s? The eugenics movement advocated selective breeding for the purpose of producing desirable human phenotypes. Should parents be able to preselect the characteristics of their children prior to birth? We will likely continue to develop reactive ethics, morals, and laws as the result of advances in the genomic sciences. We view the future of the study of heredity to include a range of social, psychological, biological, and genetic influences. Genetics serves as a necessary but insufficient factor to understand the scope of intergenerational stability and variation.

SEE ALSO Darwin, Charles; Determinism, Biological; Determinism, Genetic; Disease; Evolutionary Psychology; Genomics; IQ Controversy; Psychosomatics; Twin Studies

BIBLIOGRAPHY

Edwards, C. L., K. Whitfield, S. Sudhakar, et al. 2006. Parental Substance Abuse, Reports of Chronic Pain, and Coping in Adult Patients with Sickle Cell Disease (SCD). Journal of the National Medical Association 98 (3): 420–428.

Gillham, Nicholas Wright. 2001. A Life of Sir Francis Galton: From African Exploration to the Birth of Eugenics. New York: Oxford University Press.

Whitfield, K. E., D. T. Brandon, E. Robinson, et al. 2006. Sources of Variability in John Henryism. Journal of the National Medical Association 98 (4): 641–647.

Whitfield, K. E., G. King, S. Moller, et al. 2007. Concordance Rates for Smoking among African-American Twins. Journal of the National Medical Association 99 (3): 213–217.

Christopher L. Edwards

Goldie Byrd

Heredity

The process by which the genetic code of parents is passed on to their children.

There are certain traits that parents pass on to their children, including eye color, hair color, height, and other physical characteristics. The coding for these traits are contained inside DNA molecules that are present within all human cells. Since the discovery of DNA by James Watson (1928-) in the 1950s, the science of genetics has focused on the study of DNA and the ways in which physical traits are passed on from generation to generation. Within genetics, a special branch of DNA science—called quantitative, or biometrical, genetics— has emerged, which studies the heritability of such traits as intelligence , behavior, and personality . This branch focuses on the effects of polygenes in the creation of certain phenotypes. Polygenes, as the name implies, refer to the interaction of several genes; and phenotypes are certain variable characteristics of behavior or personality. Quantitative geneticists, therefore, study the effects of groups of genes on the development of personality and other abstract variables. They rarely, it should be noted, are able to pinpoint a behavior's genesis to a specific gene. Specific genes have been found to cause a small number of diseases, however, such as Huntington's disease and other degenerative disorders.

In studying personality traits and intelligence, the latest research in quantitative genetics suggests that the heritability rate for many characteristics hovers around 50 percent. In 1988 a study of twins reared apart revealed the heritability of 11 common character traits. The findings, published in the Journal of Personality and Social Psychology, reported that social potency is 61% influenced by genes; traditionalism, 60%; stress reaction, 55%; absorption (having a vivid imagination ), 55%; alienation , 55%; well-being, 54%; harm avoidance (avoiding dangerous activities), 51%; aggression , 48%; achievement, 46%; control, 43%; and social closeness, 33 percent.

Other recent studies have compiled lists of traits most influenced by heredity. Physical characteristics that are most genetically determined include height, weight, tone of voice, tooth decay, athletic ability , and age of death, among others. Intellectual capabilities include memory , IQ scores, age of language acquisition, reading disabilities, and mental retardation . Emotional characteristics found to be most influenced by heredity were shyness , extroversion , neuroses, schizophrenia , anxiety, and alcohol dependence. It is important to note that these are tendencies and not absolutes. Many children of alcoholics, for instance, do not become alcoholics themselves. Many social and cultural factors intervene as humans develop, and the child of an alcoholic, who may be genetically vulnerable to acquiring the disease, may avoid drinking from witnessing the devastation caused by the disease. (For a fuller discussion of the role of environment , see Nature-Nurture Controversy.)

Recent work has shown that genes can both be influenced by the environment and can even influence the environments in which we find ourselves. A 1990 study found that animals raised in environments requiring significant motor activity actually developed new structures in the brain that were significantly different from the brain structures of animals raised in environments lacking motor stimuli. Observations from such experiments have revealed that complex environments actually "turn on" sets of genes that control other genes, whose job it is to build new cerebral structures. Therefore, living in an environment that provides challenges can genetically alter a person's makeup. Additionally, a genetic predisposition to introversion can cause people to isolate themselves, thus changing their environment and, in the process, altering their development of social skills. This, then, contributes further to their genetic predisposition to introversion.

There also appears to be universal, inherited behavior patterns in humans. Common behaviors across diverse cultures include the patterns of protest among infants and small children at being separated from their mothers. A study conducted in 1976 found that separation protests emerge, peak, and then disappear in nearly identical ways across five widely diverse cultures. Other studies have found universal facial expressions for common emotions, even among pre-literate hunter-gatherer cultures that have had no exposure to media. It used to be thought that the human smile was learned through observation and imitation , but a 1975 study found that children who had been blind from birth began smiling at the same age as sighted children. Many of these behaviors are thought to be instinctual. Aside from the infant/developmental behaviors already mentioned, other inherited behavior patterns in humans include sex, aggression, fear , and curiosity/exploration.

Further Reading

Beal, Eileen. "Charting the Future? Researching Heredity Quotient in African American Families." American Visions (October-November 1994): 44.

Berkowitz, Ari. "Our Genes, Ourselves?" BioScience (January 1996): 42.

Metzler, Kristan. "The Apple Doesn't Fall Far in Families Linked to Crime." Insight on the News (29 August 1994):17.

Tellegen, A. "Personality Similarity in Twins Reared Apart and Together." Journal of Personality and Social Psychology 54 (1988): 1031.

204. Heredity

See also 15. ANCESTORS ; 44. BIOLOGY ; 147. EVOLUTION ; 307. PARENTS ; 341. RACE .

abiogenesis

generation of living organisms from inanimate matter. Also called spontaneous generation .

anencephaly

the congenital absence of the brain and spinal cord in a devel-oping fetus.

biotypology

the science or study of biotypes, or organisms sharing the same hereditary characteristics —biotypologic, biotypological , adj.

blastogenesis

the theory that hereditary characteristics are transmitted by germ plasm. Cf. pangenesis . —blastogenetic , adj.

cytoplasm

the entire substance of a cell excluding the nucleus.

deoxyribonucleic acid (DNA)

the complex substance that is the main carrier of genetic information for all organisms and a major component of chromosomes.

DNA

deoxyribonucleic acid.

dysgenesis

lack of or partial fertility, as found in hybrids like the mule, which cannot breed amongst themselves but only with the parent stock. —dysgenetic , adj.

geneagenesis

alternation of generations. —geneagenetic , adj.

genetics

1. Biology. the science of heredity, studying resemblances and differences in related organisms and the mechanisms which explain these phenomena.

2. the genetic properties and phenomena of an organism. —geneticist , n. —genetic , adj.

hereditist

a believer in the theory that heredity, more than environment, determines nature, characteristics, etc.

homogenesis

the normal course of generation in which the offspring resembles the parent from generation to generation. —homogenetic , adj,

Mendelism

the laws of inheritance through genes, discovered by Gregor J. Mendel. —Mendelian . n., adj.

pangenesis

the theory advanced by Darwin, now rejected, that transmission of traits is caused by every cell’s throwing off particles called gemmules, which are the basic units of hereditary transmission. The gemmules were said to have collected in the reproductive cells, thus ensuring that each cell is represented in the germ cells. Cf. blastogenesis . —pangenetic , adj.

perigenesis

Haeckel’s theory of generation and reproduction, which assumes that a dynamic growth force is passed on from one generation to the next. —perigenetic , adj.

prepotency

the capacity of one parent to impose its hereditary characteristics on offspring by virtue of its possessing a larger number of homozygous, dominant genes than the other parent. —prepotent , adj.

radiogenetics

a division of radiobiology that studies the effects of radioactiv-ity upon factors of inheritance in genetics. —radiogenic , adj.

recombinant DNA

a DNA molecule in which the genetic material has been artificially broken down so that genes from another organism can be intro-duced and the molecule then recombined, the result being alterations in the genetic characteristics of the original molecule.

ribonucleic acid (RNA)

a nucleic acid found in cells that transmits genetic instructions from the nucleus to the cytoplasm.

RNA

ribonucleic acid.

telegony

the supposed transmission of hereditary characteristics from one sire to offspring subsequently born to other sires by the same female. —telegonic , adj.

Weismannism

the theories of development and heredity asserted by August Weismann (1834-1914), esp. that inheritable characteristics are carried in the germ cells, and that acquired characteristics are not hereditary. —Weismannian , n., adj.

xenogenesis

1. abiogenesis; spontaneous generation.

2. metagenesis, or alternation of generations.

3. production of an offspring entirely different from either of the parents. Also xenogeny . —xenogenic, xenogenetic , adj.

xenogeny

xenogenesis.

heredity transmission from generation to generation through the process of reproduction in plants and animals of factors which cause the offspring to resemble their parents. That like begets like has been a maxim since ancient times. Although the fact of heredity has been generally known for centuries, the actual mechanisms by which inherited characteristics are transmitted to successive generations could not be satisfactorily explained until powerful enough microscopes and sufficiently refined research techniques disclosed the true nature of the universal reproductive processes of cell division and those, in "higher" animals, in which the sperm and the ovum, containing the hereditary material (see chromosome ) in their cell nuclei, unite to give rise to the new individual. Thus the science of heredity developed long after practical observations of breeding and of parent-child resemblance had been noted and also after the theory of evolution had been established. In the 18th cent. the popular concept of heredity was the theory of preformation: that the prototypical members of each organism (e.g., Adam and Eve among humans) contained within them all future generations, perfectly formed but in miniature, arranged one inside the next like a series of Chinese boxes. In the early 19th cent. Lamarck developed a theory of evolution in which the then current belief in the inheritance of acquired characteristics served as an explanation of its mechanism. The theory of pangenesis, as it was termed in a modified version in Darwinism , was strongly reminiscent of the ideas of Hippocrates and Aristotle. It hypothesized tiny particles called pangens, or gemmules—each bearing the hereditary potential for a specific body part—which circulated in the body and eventually collected in the reproductive cells. Finally, in 1875, Oscar Hertwig's principle of the universality of fertilization in sexual reproduction confirmed the transmission of hereditary material through the two sex cells. August Weismann's theory of germ plasm continuity (1892) established that the germ (sex) cells are set apart from other body cells early in embryonic development and thus that only changes in the germ plasm, and not influences on the adult body, can affect the characteristics of future generations. In 1900 the neglected work of Gregor Mendel was rediscovered and the first scientific laws for the mechanisms of hereditary were presented. These, correlating with the microscopic and experimental observations of the behavior of chromosomes and reproductive cells and later with the biochemical analyses of genes and their products, provided the basis for modern studies. Genetics is the modern science that studies the mechanisms for the transmission of hereditary information in the resulting organism. Mutation is a mechanism for evolutionary change, initiating new variations.

Bibliography: See F. Jacob, The Logic of Life (1974); J. H. Bennett, Natural Selection, Heredity, and Eugenics (1983); B. W. Winterton, The Process of Heredity (1983).

heredity The passing down by genetic transmission of the characteristics of plants or animals from one generation to the next (‘like begetting like’). The idea of biologically transmitted similarities is an old one. However, ideas as to the means of this transmission and its malleability by environmental influences have changed. Present-day ideas are grounded in research on genetics (a term first coined in 1905 for the science of heredity) that has its origins in Mendel's classic studies cross-breeding peas. This and other research provided the missing link in Charles Darwin's theory of natural selection by specifying the mechanism through which species variation and similarity could occur.

The impact of such ideas on the study of human behaviour was considerable. Francis Galton, a cousin of Darwin, explored the role of heredity in accounting for individual differences in personality and intelligence. He also introduced the term eugenics for the body of knowledge that could be used to direct human evolution–an interventionist strategy that has remained highly controversial. Subsequent academic debate, juxtaposing heredity and environment in an exhaustive specification of causal factors, has continued the attempt to assess the relative contributions of genetics and environment in the causation of human characteristics and behaviour, with individual differences receiving much of the research attention. Twin studies, comparing monozygotic or MZ (identical) twins with dizygotic or DZ (non-identical) twins have been widely employed, although the methodological difficulties are considerable. However, whilst the attempt to quantify the genetic or environmental contribution to differences between individuals continues, there is increasing recognition that both genetics and environment are essential to all human behaviour. See also GENE; NATURE VERSUS NURTURE DEBATE; SOCIOBIOLOGY.

heredity Transmission of characteristics from one generation of plants or animals to another. Characteristics, such as red hair, may be specific to individuals within a group; others, such as the possession of external ears, may be typical of a group as a whole. The combination of characteristics that makes up an organism and makes it different from others is set out in the organism's genetic code, passed on from its parents. Austrian naturalist Gregor Mendel conducted the first studies of heredity.

he·red·i·ty / həˈreditē/ • n. 1. the passing on of physical or mental characteristics genetically from one generation to another: few scientists dispute that heredity can create a susceptibility to alcoholism. ∎  a person's ancestry: he wears a Cossack tunic to emphasize his Russian heredity. 2. inheritance of title, office, or right: membership is largely based on heredity.

heredity The transmission of characteristics from parents to offspring via the chromosomes. The study of heredity (genetics) was first undertaken by Gregor Mendel (see Mendel's laws).

heredity (hi-red-iti) n. the process that causes the biological similarity between parents and their offspring. Genetics is the study of heredity.

heredity •banditti, bitty, chitty, city, committee, ditty, gritty, intercity, kitty, nitty-gritty, Pitti, pity, pretty, shitty, slitty, smriti, spitty, titty, vittae, witty •fifty, fifty-fifty, nifty, shifty, swiftie, thrifty •guilty, kiltie, silty •flinty, linty, minty, shinty •ballistae, Christie, Corpus Christi, misty, twisty, wristy •sixty •deity, gaiety (US gayety), laity, simultaneity, spontaneity •contemporaneity, corporeity, femineity, heterogeneity, homogeneity •anxiety, contrariety, dubiety, impiety, impropriety, inebriety, notoriety, piety, satiety, sobriety, ubiety, variety •moiety •acuity, ambiguity, annuity, assiduity, congruity, contiguity, continuity, exiguity, fatuity, fortuity, gratuity, ingenuity, perpetuity, perspicuity, promiscuity, suety, superfluity, tenuity, vacuity •rabbity •improbity, probity •acerbity • witchetty • crotchety •heredity •acidity, acridity, aridity, avidity, cupidity, flaccidity, fluidity, frigidity, humidity, hybridity, insipidity, intrepidity, limpidity, liquidity, lividity, lucidity, morbidity, placidity, putridity, quiddity, rabidity, rancidity, rapidity, rigidity, solidity, stolidity, stupidity, tepidity, timidity, torpidity, torridity, turgidity, validity, vapidity •commodity, oddity •immodesty, modesty •crudity, nudity •fecundity, jocundity, moribundity, profundity, rotundity, rubicundity •absurdity • difficulty • gadgety •majesty • fidgety • rackety •pernickety, rickety •biscuity •banality, duality, fatality, finality, ideality, legality, locality, modality, morality, natality, orality, reality, regality, rurality, tonality, totality, venality, vitality, vocality •fidelity •ability, agility, civility, debility, docility, edibility, facility, fertility, flexility, fragility, futility, gentility, hostility, humility, imbecility, infantility, juvenility, liability, mobility, nihility, nobility, nubility, puerility, senility, servility, stability, sterility, tactility, tranquillity (US tranquility), usability, utility, versatility, viability, virility, volatility •ringlety •equality, frivolity, jollity, polity, quality •credulity, garrulity, sedulity •nullity •amity, calamity •extremity • enmity •anonymity, dimity, equanimity, magnanimity, proximity, pseudonymity, pusillanimity, unanimity •comity •conformity, deformity, enormity, multiformity, uniformity •subcommittee • pepperminty •infirmity •Christianity, humanity, inanity, profanity, sanity, urbanity, vanity •amnesty •lenity, obscenity, serenity •indemnity, solemnity •mundanity • amenity •affinity, asininity, clandestinity, divinity, femininity, infinity, masculinity, salinity, trinity, vicinity, virginity •benignity, dignity, malignity •honesty •community, immunity, importunity, impunity, opportunity, unity •confraternity, eternity, fraternity, maternity, modernity, paternity, taciturnity •serendipity, snippety •uppity •angularity, barbarity, bipolarity, charity, circularity, clarity, complementarity, familiarity, granularity, hilarity, insularity, irregularity, jocularity, linearity, parity, particularity, peculiarity, polarity, popularity, regularity, secularity, similarity, singularity, solidarity, subsidiarity, unitarity, vernacularity, vulgarity •alacrity • sacristy •ambidexterity, asperity, austerity, celerity, dexterity, ferrety, posterity, prosperity, severity, sincerity, temerity, verity •celebrity • integrity • rarity •authority, inferiority, juniority, majority, minority, priority, seniority, sonority, sorority, superiority •mediocrity • sovereignty • salubrity •entirety •futurity, immaturity, impurity, maturity, obscurity, purity, security, surety •touristy •audacity, capacity, fugacity, loquacity, mendacity, opacity, perspicacity, pertinacity, pugnacity, rapacity, sagacity, sequacity, tenacity, veracity, vivacity, voracity •laxity •sparsity, varsity •necessity •complexity, perplexity •density, immensity, propensity, tensity •scarcity • obesity •felicity, toxicity •fixity, prolixity •benedicite, nicety •anfractuosity, animosity, atrocity, bellicosity, curiosity, fabulosity, ferocity, generosity, grandiosity, impecuniosity, impetuosity, jocosity, luminosity, monstrosity, nebulosity, pomposity, ponderosity, porosity, preciosity, precocity, reciprocity, religiosity, scrupulosity, sinuosity, sumptuosity, velocity, verbosity, virtuosity, viscosity •paucity • falsity • caducity • russety •adversity, biodiversity, diversity, perversity, university •sacrosanctity, sanctity •chastity •entity, identity •quantity • certainty •cavity, concavity, depravity, gravity •travesty • suavity •brevity, levity, longevity •velvety • naivety •activity, nativity •equity •antiquity, iniquity, obliquity, ubiquity •propinquity