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Chapter 3

Chapter 3 study guide: Genetic and Biological Foundations

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University of Toronto St. George
Michael Inzlicht

Chapter 3: Genetic and Biological Foundations What is the Genetic Basis of Psychological Science? Within nearly every cell in the body is the genome for making the entire organism: It is the mater recipe that provides retailed instructions for everything from how to grow a gall bladder to where to place the nose on your face. The term genetics is typically used to describe how characteristics, such as height, hair colour, and weight, is passed along through inheritance, but it also refers to those processes that are involved in turning genes off and on. Within each cell are chromosomes, which are structures made up of genes. The typical human has 23 chromosomes, half of each pair coming from each parent. Proteins, of which there are thousands of different types, are the basic chemicals that make up the structure of cells and direct their activities. A gene is a segment of DNA that is involved in producing proteins that carry out specific tasks. The process by which the gene produces RNA and then protein is known as gene expression, in that the gene is switched on Genes provide options, and the environment determines which option is taken. Gene expression not only determines the physical makeup of the body but also remains important throughout life and is involved in all psychological activity. It is the gene expression that allows us to learn, to see, and to fall in love. Heredity Involves Passing along Genes through Reproduction The first clues to the mechanisms responsible for heredity were discovered by the monk Gregor Mendel around 1866. Mendel developed an experimental technique called selective breeding for studying genetics. E.g. Mendel used a flower with 2 types of colours to control which plants were bred with which other plants. Mendel cross-pollinated two types of plants to see which colour flowers would be produced. Mendel deduced that there must be discrete units, now referred to as genes, which exist in two versions. The two versions of genes are known as alleles. If alleles differ, one is dominant and the other is recessive. Dominant genes are expressed (become apparent) whenever they are present. Recessive genes are expressed only when they are matched with a gene from the other parent. Genotype and Phenotype The existence of dominant and recessive genes means that not all genes are outwardly expressed. The genotype is the genetic constitution of an organism, the actual y l genetic makeup that is determined at the moment of conception. The phenotype is the observable physical characteristics of an organism that result from both genetic and environmental influences. www.notesolution.com The environment can also affect the phenotype; for instance, good nutrition leads to increased physical size and a suntan changes the colour of the skin. E.g. Example of environmental influence on the phenotype is phenylketonuria, a disorder in which infants are unable to break down and enzyme contained in dairy and other products, such as the sweetener aspartame. Polygenic Effects When there are a range of variability within a population for certain characteristics, such as height, this indicates the characteristic is polygenic, that is influenced by many genes, as well as the environment. Most human traits and diseases are polygenic. Genotypic Variation is created by Sexual Reproduction A fertilized cell, known as a zygote, contains 23 pairs of chromosomes, one half of each pair from the mother and the other half from the father. rd The two chromosomes in the 23 pair are the sex chromosomes, denoted X and Y due to their shapes. Females have two X chromosomes, whereas males have one X and one Y chromosomes. A zygote is one of 64 trillion possible combinations. Cell division is the basis of the life cycle and is responsible for growth and development. Sometimes there are errors in this process, which lead to mutations, most of which are benign and have little influence. Genes Affect Behaviour The study of how genes and environment interact to influence psychological activity is known as behavioural genetics. People are born essentially as undeveloped photographs: the image is already captured, but the way it eventually appears can vary based on the development process. Behavioural Genetics Methods Behavioural geneticists use two basic methods to assess the degree to which traits are inherited: twin studies and adoption studies. Twin studies compare similarities between different types of twins to determine the genetic basis of specific traits. Monozygotic twins, also called identical twins are the result of one zygote dividing into two, each having the same chromosomes and the genes they contain. Dizygotic twins, sometimes called fraternal or non-identical twins, are the result of two separately fertilized eggs and are no more related than any other pair of siblings. Adoptive studies compare the similarities between biological relatives and adoptive relatives. Identical twins are more likely to be similar whether they were raised together or not. It is clear that twins share similarities other than just behaviour quirks, such as intelligence and personality. Understanding Heritability Heredity is the transmission of characteristics from parents to offspring by means of genes. Heritability is a statistical estimate of the portion of observed variation in a population that is caused by differences in heredity. www.notesolution.com
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