Biology and Behaviour Flashcards
Nature and Nurture
model of hereditary and environmental influences:
there are three key elements of the model,
genotype - genetic material individual inherits. also can refer to the two alleles inherited for a particular gene.
phenotype - observable expression of the genotypes, including both body characteristics and behaviour (observable traits such as height, eye color, and blood type)
environment - every aspect of the individuals surroundings.
These three elements are involved in 5 relations that are fundamental in the development of every child:
- Parents Genotype contributing to child Genotype
Involves the transmission of genetic material from parent to offspring. the gametes conjoin at conception to create a zygote. the nucleus of every cell in the body contains chromosomes made up of DNA (deoxyribonucleic acid). DNA carries biochemical instructions that are “packaged” in genes. genes affect the development and behaviour only through the manufacture of proteins. Researchers have discovered genes make up only 2% of the human genome. most of the rest of our genome - once thought to be “junk” DNA - turns out to play a supporting role in influencing genetic transmission by regulating the activity of protein-coding genes.
human heredity - your biological children will receive half of your genes, and you biological grandchildren will have one-quarter.
sex determination - it is always the father who determines the sex of offspring - it is the presence of the Y-bearing sperm that makes an individual male.
diversity and individuality - mutation (a change that occurs in a section of DNA) contributes to genetic diversity among people. some mutations are random spontaneous errors; others are caused by environmental factors. most are harmful (inherit diseases/disorders), however they make you more likely to survive. second mechanism that promote variability is random assortment of chromosomes in the formation of egg and sperm. each gamete has many possible combinations of chromosomes. thus, no two individuals would have the same genotype. ‘crossing over’ is also a process of variation where two members of a pair of chromosomes swap sections of DNA. as a result, some of the chromosomes that parents pass on to their offspring are consitituted differently from their own.
assortment and crossing over shape the degree to which a child will resemble one parent, and the degree to which they will vary.
- the contribution of the childs genotype to their own phenotype.
gene expression - Developmental changes:
genes influence development and behaviour only when they are turned on, and human development process normally, from conception to death, only if genes get switch on and off in the right place, at the right time. the switching off and on of genes is controlled by regulator genes. the activation/inactivation of one gene is always part of a chain of genetic events. thus, genes never function in isolation. the expression of one gene is a precondition for the expression of another. External factors such as thalidomide (a drug) can affect the switching on and off of genes. this on-again, off-again functioning of individual genes results in enormous diversity in genetic expression.
Gene expression - Dominance patterns:
many genes are never expressed, one reason is known as alleles which influence the same trait or characteristic such as eye colour but contribute to different developmental outcomes (e.g. brown, blue, hazel, grey eyes). dominant-recessive pattern can be explained by genes only having two alleles, one which is dominant and the other recessive. two possibilities:
1) homozygous - person inherits two of same allele
2) heterozygous - person inherits two different alleles
polygenic inheritance involves (inheriting traits such as shyness, aggression, thrill-seeking, and language learning) many different genes contributing to any given phenotypic outcome.
- the contribution of the child’s environment to their phenotype.
examples of genotype-environment interaction:
- phenylketonuria (PKU) - a disorder related to a defective recessive gene on chromosome 12 that prevents metabolism of the amino acid phenylalanine.
- abusive parenting - 85% who had a relatively inactive MAOA gene and experienced abuse grew up to be more antisocial and 10 times more likely to be convicted of a violent crime
parental contributions to child’s environment:
the environment parents provide for their children is due in part to the parent’s own genetic makeup (gene-environment correlations). parents behaviour toward their children is genetically influenced, as are the resources to which they expose their children to.
- the contributions of the child’s phenotype to their environment.
restates the active child (being a source of their own development). how do they create their own environment?
- by virtue of their nature and behaviour, they actively envoke certain kinds of responses from others.
- by actively selecting surroundings and experiences that match their interests, talents, and personality characteristics. Choosing their own environment and activities contributes to the child’s intellectual development.
- the contributions of the child’s environment to their genotype.
certain epigenetic mechanisms, mediated by the environments, can alter the functioning of genes and create stable changes in their expression (a process called methylation which silences gene expression) - and some of these changes can be passed on to the next generation.
epigenetic factors can help explain why identical twins do not have identical pathways through life; different environments can alter gene expression in subtle ways across developmental time. differences in experience over the course of development are reflected in differences in methylation levels.
children experiencing stress (abuse) has epigenetic effects.
all in all, children’s experience can change their genetic expression through epigenetic mechanisms.
Behaviour Genetics
the field of behaviour genetics is concerned with how variation in behaviour and development results from the interaction of genetic and environmental factors.
Galtons question: why are people different from one another?
to answer his question two premises have to be considered:
- genetic factors are important for a given trait or behaviour, individuals who are genotypically similar should be phenotypically similar. in other words, behaviour patterns should “run in families”: children should be more similar to their parents and siblings than to second- or third-degree relatives or unrelated individuals
- shared environmental factors are important, individuals who were reared together should be more similar than people who were reared apart
Behaviour Genetics
Behaviour Genetics Research Designs
In order to examine genetic and environmental contributions to a given trait or characteristics, behaviour geneticists first measure that trait in people who vary in terms of genetic relatedness.
next, they assess how high correlated the measures of the trait are among individuals who vary in the degree to which they are genetically related.
Finally, behaviour genticists comparing the resulting correlations to see if they are:
1) higher for more closely related individuals than for less closely related people
2) higher for individuals who share the same environment than for individuals who do not.
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several specialised family-study designs to assess genetic and environmental influences.
1) twin-study design:
compares the correlations for MZ or DZ twins with those for same-sex fraternal (dizygotic, or DZ) twins. equal environments assumption is the claim that both types of twins shared the womb, were born at the same time, have lived in the same family and community, and are always the same age when tested. thus, with different levels of genetic similarity and essentially equal environmental similarity, the difference between the correlations for the two types of twins is treated as an index of the importance of genetics factors. if the identical twins on a given trait or behaviour has a substantially higher correlation than that between fraternal twins, it is assumed that genetic factors are substantially responsible for the difference.
2) Adoption study:
examine whether adopted children’s scores on a given measure are correlated more highly with those of their biological parents and siblings, or those of their adoptive parents and siblings.
3) adoptive twin study:
compares identical twins who grew up together vs. identical twins reared apart shortly after birth. if the correlations for twins reared apart are similar to those for twins reared together, it suggests that environmental factors have little effect. if they are lower, environmental influence is inferred.
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Family Studies of Intelligence
both genetic and environmental influences. genetic influence is shown by generally higher correlations for higher degrees of genetic similarity. most notable is the finding that MZ twins resemble each other in IQ more than DZ twins. environmental influences are reflected in the fact that MZ twins are not identical in terms of IQ, as well as MZ twins who are reared together are more similar than those reared apart.
does the influence of genes and environment have on intelligence chance over the course of development? Surprisingly, as twins get older, the degree of variance in IQ accounted for by their genetic similarity increases. as children have more opportunities to shape their own environments based on their genetic propensities, the genetic effects of intelligence become more prominent.
Behaviour Genetics
Heritability
a statistical estimate of the proportion of the measured variance on a trait among individuals in a given population that is attributable to genetic differences among those individuals.
crucial point in understanding heritability:
tell us nothing about the relative contributions of genetic and environmental factors to the development of an individual. Instead, they estimate how much of the variation among a given population of people is due to differences in their genes.
the heritability estimate of intelligence is 50%.
Genome-wide association studies (GWAS) are used in attempts to link specific DNA segments with particular traits. these studies have revealed that genetic effects are cumulative (increased).
criticisms of heritability estimates:
- the term heritability is often misinterpreted or misused.
common misunderstandings:
- applying the concept of heritability to an individual, despite the fact that heritability applies only to population.
- applying the concept of heritability to a wide population when in fact can only be used on a particular population living in a particular environment.
- the estimates can differ markedly for groups of people who grow up in very different economic circumstances.
- high heritability does not imply immutability (does not mean that there is little point improving the course of development related to that trait.)
- equal environments assumption: claim underlying many behaviour genetic designs, that MZ twins share environments that are equally simular as those shared by DZ twins.
new approaches to studying heritability:
A contemporary method such as genome-wide complex trait analysis (GTCA) takes advantage of actual genetic resemblance across large groups of individuals (can tease apart aspects of genes and environment confounded within families), rather than estimates of genetic resemblance based on family relationships.
advantages of GCTA:
- goes beyond adoption and twin studies to consider actual genetic overlap among unrelated people.
- researchers found that children’s educational attainments and social advantage appear to share some of the same genetic roots.
- GTCA allowed researchers to determine whether the same genes are implicated in measures of a particular trait across development.
- may help us better understand the relationship between the brain and complex behaviours like intelligence or academic achievement.
Behaviour Genetics
environmental effects
heritability estimates rarely exceed 50%, a large contribution from environmental factors is usually indicated.
Behaviour geneticists assess the extent to which aspects of an environment shared by biologically related people make them more alike and to what extent non-shared experiences make them different.
shared environment effects can:
- be inferred when twins or other relatives are more similar on some trait than would be expected on the basis of their genetic relatedness
- also being discovered for disorders that have a clear genetic component
however, in a recent large-scale study of twin pairs in which at least one co-twin had an ASD diagnosis, researchers found a substantial shared environment effect on the likelihood that the second twin also has an ASD diagnosis.
non-share environment effects:
children who grow up in the same family do not always have all their experiences in common, due to
-family structure
-parents behaving differently towards them
-different peer groups
-idiosyncratic life events (accident, bullied, inspired by someone)
Brain Behaviour
Structures of the Brain
focusing on the neuron and cortex, as well as some of their substructures.
Neurons are the basic units of the brains informational system. sensory neurons transmit info from sensory receptors that detect stimuli in the external environment or within the body, motor neurons transmit info from the brain to muscles and glands, and interneurons act as intermediaries between sensory and motor neurons. All neurons have three components, a cell body (contains the basic biological material that keeps the neuron functioning), dendrites (fibers that receive input from other cells and conduct it toward the cell body in the form of electrical pulses) and an axon (a fiber that conducts electrical signals away from the cell body to connections with other neurons). these cells transmit info via electrical signals. impulses are transmitted from one neuron to another at synapses either to fire, sending signal on to other neurons, or to be inhibited from firing.
Glia cells are another important component to the brain which perform a variety of critical functions, including the formation of a myelin sheath around axons, which insulates them and increases the speed and efficiency of info transmission. Importance of glia cells in brain health including mental illness and disease if these cells are affected.
the most human part of the human brain is the cortex, because it is involved in a wide variety of higher mental functions. different areas of the cortex are specialised for general behavioural categories (occipital, temporal, parietal, and frontal lobes). the cortex, is divided into two cerebral hemispheres, where the corpus callosum is a dense tract of nerve fibers that enable the two hemispheres to communicate, each of which is specialised for certain modes of processing, a phenomenon known as cerebral lateralisation
brain development involves several processes, beginning with neurogenesis (the proliferation of neurons through cell division) and differentiation of neurons. in synaptogenesis, an enormous profusion of connections among neurons is generated, starting prenatally and continuing for the first few years after birth. through synaptic pruning, excess connections among neurons are eliminated (synapse elimination).
experience plays a crucial role in the strengthening or eliminating of synapses and hence in the normal wiring of the brain. the fine-tuning of the brain involves experience-expectant processes in which existing synapses are preserved as a function of stimulation that virtually every human encounters, and experience-dependent processes, in which new connections are formed as a function of experience and learning.
plasticity refers to the fact that nurture is the partner of nature in the normal development of the brain. this fact makes is possible in certain circumstances for the brain to rewire itself in response to damage. is also makes the developing brain vulnerable to the absence of stimulation at sensitive periods in development.
the ability of the brain to recover from injury depends on the age of the child. very early damage, during the time when neurogenesis and synaptogensis are occurring, can have especially devastating effects.
The Body: Physical Growth and Development
humans undergo a particularly prolonged period of physical growth, during which growth is uneven, proceeding more rapidly early in life and in adolescence. secular trends (marked changes in physical development that have occurred over generations) have been observed in increases in average weight and height. Failure to thrive is a condition in which infants become malnourished and fail to grow or gain weight for no obvious medical reason.
food preferences begin with innate responses by newborns to basic tastes, but additional preferences develop as a result of experience. problems with the regulation of eating are evident in the United States, where an epidemic of obesity is clearly related to both environmental and genetic factors.
in much of the rest of the world, the dominant problem is getting enough food. inadequate nutrition is closely associated with poverty and it leads to a variety of behavioural and physical problems in virtually every aspect of the child’s life. prevention of undernutrition is needed to allow millions of children to develop normal brains and bodies.
