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Genetics and Intelligence

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Queen's University
PSYC 100

Genetics and Intelligence Nativism -philosophical view that we are born with knowledge already present -genes -innate/hard-wired-> not affected by experiences -nature Empiricism -philosophical view that we obtain all knowledge through our senses -blank slate -behaviour results from individual experiences -nurture -nature vs. nurture-> false dichotomy-> for example, the diathesis-stress model of mental illness show that genes interact with the environment at every level Behaviour Genetics -study of how genes and environment influences on behaviour -founded by John Scoot, John Fuller, and William R. Thompson-> studied personality traits in dog breeds -methods applied to humans typically involve comparing people of different levels of relatedness, such as parents and their offspring, siblings and unrelated individuals, and measuring resemblances for a specific trait of interest -for example, an individual born to parents who have alcohol problems might inherit the genes that create a sensitivity for alcohol, but they must decide to drink -studied adopted children to estimate genetic contributions to behaviour-> biological parents (nature) and adopted parent (nurture)-> heritability increases with age, whereas the opposite is true for depression and anxiety -Robert Plomin and Spinath describe it as a three-layered approach, with each layer asking different, yet related questions: Genetics- to what degree is intelligence an inherited trait? Genes- if intelligence does have a genetic component, which genes are involved? Genome- if we can identify which genes contribute to intelligence, then how exactly do they contribute to brain development and function? -sexual reproduction involves the combining of genetic material from a male and a female through the union of a sperm and an egg DNA (Deoxyribonucleic Acid) -genetic material of all organisms that makes up chromosomes -molecule formed in a double-helix shape that resembles a twisted ladder, with strands of sugar and phosphates connected by rungs made from nucleotide molecules of adenine, thymine, guanine, and cytosine-> amino acids-> typically abbreviated using the first letter of their names- > A, T, G, and C-> each gene is a unique combination of the four amino acids that is used to different tasks-> for example a sequence of amino acids on a certain gene may be AGCCTAATCG, and so on Code - sequence represents it used to create proteins Chromosomes -threadlike structures in the nuclei of living cells -contain genes -human has twenty-three pairs-> twenty-two are autosomes and the twenty-third pair is made up of X and Y chromosomes-> males have and XY pair, and females have an XX pair Meiosis -process where the sperm and egg cells are produced -results in each cell having only half of each pair of chromosomes-> when sex cells combine during reproduction, the half pairs combine to give the resulting cell a complete set of twenty-three pairs of chromosomes Chromatid -one of two identical halves of a replicated chromosome -mother has two Xs -father has a X chromatid or a Y chromatid because he has both X and Y chromosome -sperm makeup determines the sex of the offspring-> but the way the genes are combined are more complex than attributing half the characteristics to one parent and half of the other -all workings of cells are controlled by proteins Genes -small units of DNA and heredity that direct the synthesis of proteins and enzymes -result in the expression of inheritable traits-> makes up our physical structures and regulate development and physiological process throughout the life span -regions of chromosomes that encode particular proteins -found in the nucleus found in cells Encode - transfer genetic information from DNA to proteins Locus -point on the chromosome where a particular gene is located -Loci for plural -chromosomes come in pairs, genes on one chromosome of the pair may or may not be exactly the same as the gene on the other chromosome of the pair at the same locus Homozygous -each parent contributes the same allele for a particular gene -when genes at the same locus on the two chromosomes are the same Heterozygous -each parent contributes different alleles for a particular gene -when genes at the same locus on the two chromosomes are not the same Alleles -alternative forms of the same gene -pair of genes at a given locus-> one inherited from the father, the other from the mother -if they are different than one is more dominant than the other Dominant -trait that is exhibited when an individual possesses heterozygous alleles at that locus -characterized has a capital letter-> for example ‘BB’ -for example brown hair and brown eyes Recessive -trait that occurs only when it is expressed by homozygous alleles -for example blue eyes and red hair -characterized has lower letter-> for example ‘bb’ -shows up phenotypically in subsequent generations when an organism carrying the recessive trait breeds with another one carrying it-> for example, two brown-eyed parents with genotype ‘Bb” can produce offspring who are blue-eyed ‘bb’ or brown- eyed ‘BB’/’Bb’ -person with one dominant and one recessive allele would look like ‘Bb’ -appearance and behaviour depend on environment and genes -genes don’t directly influence behaviour, they guide cells to generate proteins that causes our cells to form chemicals in the body that are related to behaviour, such as neurotransmitters and proteins Heritability -amount of changeability in a given trait in a given population at a given time due to genetic factors -statistic, expressed as a number between zero and one -measured as and sometimes known as h 2 -estimates for a given population or group may not generalize to other populations or groups -inherited traits, one passed on through genes, can have high or low heritability -traits not inherited has zero heritability-> genes don’t contribute to trait -one indicates that genes account for all individual differences in a trait -usually falls somewhere between zero or one, rarely is it purely zero or one -estimates depend on the degree where individuals in the studied population has less genetic variability-> smaller populations and relatively isolated would have less genetic variability Genotype- an organism's genetic makeup Phenotype-outward expression of an organism's genotype -an organism's physical characteristics and behaviour -produced through the interaction of genotype with the environment-> even before conception Single-Gene Effect -when two individuals have the same phenotypes but different genotypes -for example, both individuals can have brown eyes, but one individual may have it because the allele for brown eyes are more dominant, and a person who has one allele for brown eyes and one for blue eyes will be the same as an individual whose alleles are both brown Polygenic -trait that is influenced by more than one pair of genes -for example, Labrador retrievers have two separate gene for fur colour, B and b genes control color, and E gene controls the expression of B and b-> B allele produces black fur, and b allele produces brown fur-> E allele allows the fur to remain the colour that the B or b allele is coded for (black or brown), but if the dog has two e alleles, then the dog will be golden regardless of the B or b allele -most behaviours, diseases, and disorders have a polygenic basis because most genes have multiple functions -depends on a continuum of behaviour Concordance -expression of similarity in traits (or absence of traits) by both twins -often seen in studies comparing identical (monozygotic twins who arise form one fertilized egg (ovum) and have nearly identical genotypes to fraternal (dizygotic) twins who arise from separate eggs fertilized by two different sperm cells that share the same womb and are no more genetically similar than two siblings form the same parent -for example, one twin study determined the degree where anxiety and depression are influenced by genetics in children and adolescents-> more likely for both monozygotic twins to show anxiety or depressive symptoms than for both dizygotic twins to do so-> demonstrates the influential role that genes play in depression Epigenetics -study of heritable changes that occur without a change in the DNA sequence. -also describes less-common changes that pass from one organism to its descendants through sexual reproduction -cells contains instructions for the body-> external factors (chemical, social, etc.) change how the cell expresses its instructions-> altered cells continue to pass on new instructions and may pass new shape to the next generation Differentiated Cells -less-specialized cells whose profiles or characteristics have, over time, grown increasingly different from and more specialized than other cells of the same type -for example, a single-cell zygote develops into a multicellular zygote Tags - turns genes on and off Correlation - comparing two or more variables to determine if they are related-> doesn’t equal causation-> one doesn’t affect the other -some studies tell us about population effects, not individual effects-> findings can be generalized to similar populations by not targeted to individuals Differential Approach -approach in psychology devoted to tests and measures of individual differences in various psychological properties, including people's abilities to solve problems Sir Francis Galton -believed intelligence is biologically based and must be related to other biologically based phenomena and other biologically based attributes, such as head size, sensory discrimination ability, and neural quickness-> believed it could have enormous practical implications-> for example, there would be no need to spend money on schooling the less intelligent because they will never change because they were born less intelligent-> failed -inspired the creation of the statistical test of correlation and tried to find relationships between various measures and intelligence -tried to correlate more general descriptions of intelligence to physical factors-> not related to causation Neural Quickness - speed at which a person processes information Charles Spearman -techniques were used to argue against general inteligence Factor Analysis-statistical technique that reveals similarities among a wide variety of items -way to determine correlation between individual items on a test -if a group of test items correlate highly with each other, it provides evidence that they are measuring the same thing -form of mathematical modeling that examines a group of variables and looks for the underlying structure or dimensions that connect them by calculating the extent where the observed variables can be explained in terms of a smaller number of variables-> Factors Indifference of the Indicator -refers to finding that the content of the test items and the nature of the task used to test general intelligence didn’t seem to matter much in terms of test scores -for example, people who did well on hard tests of vocabulary also did well on easy mathematics tests, regardless of test format -all measures of intelligence correlated positively, he reasoned that they must all reflect a common factor of intelligence, which he called G, for general intelligence-> concept that intelligence is a basic cognitive trait comprising the ability to learn, reason, and solve problems regardless of their nature -correlating intelligence tests to each other-> leads researchers to suspect that some connection does exist and gives guidance on how to identify what it is and how it works -idea of innate differences in mental ability causes people to question the notion that ‘we are all born equal’, also strikes at the notion that equalizing education opportunities or removing socioeconomic disparities will equalize the intelligence Alfred Binet -believed that intelligence is a collection of higher-order mental abilities -believed that interaction with the environment was an important factor, more important than genetics alone and his measurements of intelligence were intended to identify children who were less intelligent so that they could receive special education-> unlike Galton Binet-Simon Scale -developed an intelligence test with Theodore Simon -test was designed to identify mentally challenged children by assessing scholastic skills, for example, memory, vocabulary, and common knowledge)-> succeeded -Mental Age-test outcome -description of the child’s score in terms of how it compared to score of an average child of a particular age -for example, a seven year old child with a mental age of seven would be considered average because her mental age matches her chronological age, but an eight year old performing at the level of a ten year old was said to have the mental age of a ten year old -reflects progress in school -originally saw the test as a measure of achievement not innate capacity Stanford-Binet Scale -revised the Binet-Simon Scale -intended to measure innate (genetic intelligence) -reflects a person’s ability -Lewis Terman William Stern Intelligence Quotient (IQ) -measurement where the mental age of an individual is divided by the person’s chronological age and then multiplied by a hundred-> Ratio IQ -for example, a ten year old child with a mental age of seven would habve an IQ of 7/10X100=70 -revised concept of mental age -problem was that although one’s mental age eventually stops changing, one’s chronological age increases until death, which changes the denominator and thus ratio IQ decreases with age-> for example, a twenty year old with a mental age of a thirty year old has a high IQ than an eighty year old with a mental age of a thirty year old-> but it was intended to measure the intelligence in schoolchildren but it’s often used to describe intellectual ability in adults too David Wechsler Deviation IQ -overcomes the problem with Ratio IQ -procedure for computing the intelligence quotient -compares an individual's score with those received by other individuals of the same chronological age -made the IQ score relative to one’s age group-> arbitrarily chose a score of a hundred to describe the average score of a given age group-> scores are distributed on a normal curve around this average point -believed that intelligence was made up of multiple abilities that couldn’t be represented adequately with one or two scores from the Stanford-Binet test-> developed intelligence tests that assessed a number of subcategories of intelligence and gave scores on each of these categories Tests started dividing the tasks into two major categories: Verbal IQ and Performance (nonverbal) IQ-> further divided into subscales that measured various specific abilities (for example, vocabulary or block design)-> scales are regularly revised in light of research findings -developed two very popular IQ tests: Wechsler Adult Intelligence Scale (WAIS)-current version contains four scales with ten subsets that contribute to the Full-Scale IQ -for sixteen year olds to ninety years old Full Scale IQ General Ability Index Cognitive Proficiency Index Verbal ComprehensioPerceptual Speed Perceptual Reasoningdex Index -similarities -block design -sym-digit span Wechsler Intelligence Scale for Children -vocabulary -matrix reasoning -cod-arithmetic (WISC) -information -visual puzzles -for most intelligent tests used today, one standard deviation above or below the average is equal to fifteen point, because IQ scores are now compared to others in the same age group and is no longer a ratio quotient Designing an Intelligence Test Standardization-determining typical performance on a test -allows for comparisons across individuals Norms-data and statistics concerning comparison groups that permit an individual's score to be assessed relative to their peers -cannot be generalized to other groups -generally established by giving a test to hundreds of people and then calculating the mean and the standard deviation -standardizing and determining norms is to make sure the test is capable of making the differentiations we’re interested in-> for example, if a test is too east or too hard, it won’t be able to asses anything of value Reliability-repeatability of a measurement -likelihood that if the measurement were made again, it would yield the same value -consistency Validity-degree where the operational definition of a variable accurately reflects the variable it is designed to measure or manipulate. -measures what it’s intended to measure -one way to asses is to compare the test with criterion measure (for example, other tests that are accepted measure, such as the correlation of the results of the an intelligence test with something like scholastic performance Using Intelligence Tests -originally used for educational purposes, but adapted to different situations-> for example, during World War I, the United States Army administrated an early Stanford-Binet intelligence test to all draftees-> many people who used the test didn’t understand the mathematical implications of a ratio test-> many early tests contained questions that showed class and language bias-> results was that the average American male was not intelligent-> early advertising industries and most industrial education programs were organized around the belief that most people are not very intelligent-> cause people to still distrust the idea of quantifying intelligence -more recent rests are carefully checked for class and language bias, and the use of deviation IQ has made the tests more reliable Schmidt and Hunter Personnel Selection-important because the hiring process is expensive and workers exhibit
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