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Chapter 4

Chapter 4 – Genes.docx

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Western University
Psychology 1000
Mark Cole

Chapter 4 – Genes, Evolution, and Behavior Genetic Influences - Genetic endowment combines environmental forces to determine our behavior - A combination of nature and nurture - Favorable and unfavorable environmental conditions affect the genetically inherited potential of an organism Chromosomes and Genes - Hipporcrates suggested that semen contains the design for the formation of offspring - Mendel did research with garden peas which marked the beginning of modern genetic theory o Showed that hereditary involves the passing on of specific organic factors which produce visible characteristics in the offspring o These factors may be carried for possible transmission to another generation o The offspring of one set of parents do not all inherit the same traits Genotype: the specific genetic makeup of an individual - Like the commands of a computer - Some of the directives are used on one occasion and some on another - Some of the directives are never used - These are present from conception and NEVER change Phenotype: the observable characteristics produced by the genetic endowment - Can be affected by other genes and by the environment Chromosomes: eggs and sperm carry the material of a hereditary in the form of rod like units - It is a tightly coiled molecule of DNA that is partly covered by a protein - It carries hereditary blueprints in genes - Genes are like a computer of info about your characteristics and limitations - Every cell in the body except the sex cell has 46 chromosomes (23 from the mom and 23 from the dad = zygote) o The sex cell has only 23 individual cells o The genes in each chromosome are formed in pairs from each parent - Genes code for the production of proteins o Proteins control the structure of the individual cells and all the chemical reactions o Half of all genes target the brain o When the gene is activated, the cell produces the specified protein in response to different metabolic rates and different environments - Alleles are alternative forms of a gene that produce different characteristics Dominant: the particular characteristic that it controls will be displayed Recessive: the characteristic will not show up unless the partner gene inherited from the other parent is also recessive - Recessive genes can be passed on to the offspring Polygenic Transmission: complicates the straightforward picture that would occur if all characteristics were determined by one pair of genes - Magnifies the number of variations in a trait Mapping the Genetic Code - The genetic structure in every one of the 23 chromosome pairs has been mapped by using methods that allowed the researchers to disassemble the genes on each chromosome and study the specific sequence of substances that occur - They discovered that humans have fewer genes than expected (25,000 compared to 100,000) Genetic Engineering - Recombination of DNA = researchers use certain enzymes to cut the long threadlike molecules of genetic DNA into pieces, combine them with DNA from another organism, and insert them into the host organism o The new DNA combination continues to divide and produce many copies of itself o They have used this to produce human growth hormone very had to maintain) which helps with height growth, etc o They have also inserted new genetic material into viruses that can infiltrate neurons and modify their genetic structure Gene Knockout: the particular function of the gene is eliminated - Insert genetic material that will prevent neurons from responding to a particular neurotransmitter and then measure whether the animals ability to learn or remember is affected - Problem: very few behaviors are controlled by only one gene Behavioral Genetic Techniques - The probability of sharing a genetic gene with your parents, as well as siblings, is 50% - The probability of sharing a genetic gene with your grandparents, as well as half-siblings, is 25% - The probability of sharing a genetic gene with your adopted parents is 0 Heritability Coefficient: variation in a particular characteristic within a group can be attributed to genetic factors - A way of estimating how much of that variation is attributable to genetic factors - Example) If the environment doesn’t account for the variation in intelligence, then the differences are due to genetic factors and the heritability coefficient is HIGH (vise-versa) - If a characteristic has higher co-occurrence in people who are related, then this relates to a possible genetic contribution (especially if they live in the same environment) Heritability: how much of he variation in a characteristic within a population can be attributed in genetic differences - Applies only to differences within a group, NOT differences between groups Adoption Study: where a person who was adopted early in life is compared on some characteristic with their biological and adoptive parents - If the adopted child and biological parents are more similar, then a genetic influence is present - If the adopted child and the adoptive parents are more similar, then an environmental influence is present Twin Studies: one of the most powerful techniques used in behavioral genetics - If identical twins are more similar to each other then fraternal twins, then a genetic factor is present - HOWEVER, identical twins are more likely to be treated the same due to the same appearance, etc - Some studies look at twins who were separated early in life and raised in different environments - Fraternal twins seem to be more similar to their biological parents - Criminal behavior of sons who’s biological fathers had criminal records were higher than when their adoptive parents had no record - ALSO, sons who had both their biological and adoptive father with records were even more likely to have a record themselves Genetic Influences on Behavior Hereditary, Environment, and Intelligence - Suppose that intelligence is determined by ONLY genes o Two people with the same genes would have identical test scores and a correlation of +1.00 o Nonidentical people, fraternal twins, share only half of the same genes and would have lower correlation scores (same as parents and kids) o The correlation for identical twins raised apart is lower than that of identical twins raised together - The more genes people have in common, the more similar they are in IQ - ALSO, the environmet contributes significantly to intelligence - ENVIRONMENT and HEREDITERY INTERACT!! Biological Reaction Range, the Environment, Personality, and Intelligence Reaction Range: for a genetically influenced trait is the range of possibilities that the genetic code allows - Means that an individual inherits a range for potential intelligence that has upper and lower limits - Environmental effects will then determine where the person falls within the genetically determined boundaries - They are influenced by our genetic inheritance and the opportunities we are given and choose to take in our environment - They cant be measured directly and differ from each person - Example) If the ranges are large, 15-20 points on the IQ scale, the environmental influence would be very high - Intellectual growth also depends on our interests, motivation, and personal characteristics on how we apply ourselves to the world!! Behavior Genetics and Personality - Eysenck argued th
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