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BRAIN & BEHAVIOUR Introduction to Brain & Behaviour- Session 3 Likitha S Department of Psychology  Psychological researchers study genetics to better understand the biological factors contributing to certain behaviours. W...

BRAIN & BEHAVIOUR Introduction to Brain & Behaviour- Session 3 Likitha S Department of Psychology  Psychological researchers study genetics to better understand the biological factors contributing to certain behaviours. While all humans share certain biological mechanisms, we are each unique. And while our bodies have many of the same parts—brains and hormones and cells with genetic codes—these are expressed in a wide variety of behaviours, thoughts, and reactions. Why do two people infected by the same disease have different outcomes: one surviving and one succumbing to the ailment? How are genetic diseases passed through family lines? Are there genetic components to psychological disorders, such as depression or schizophrenia? To what extent might a psychological basis exist for health conditions such as childhood obesity?  Theory of evolution by natural selection: In Theory of simple terms, the theory states that organisms natural selection that are better suited for their environment will survive and reproduce, while those that are poorly suited for their environment will die off.  Everything you do depends on both your genes and your environment. Without your genes or without an adequate environment, you would not exist. The controversies arise when we discuss how The Genetics of strongly genes and environment affect various Behaviour differences among people. For example, do differences in human intelligence depend mostly on genetic differences, mostly on environmental influences, or on both equally? Neither Darwin nor Wallace understood the basis of the great variation in plant and animal species they observed.  Another scientist, the monk Gregor Mendel, discovered one principle underlying phenotypic variation and how traits pass from parents to their The Genetics of offspring. Behaviour Through experiments he conducted on pea plants in his monastery garden beginning about 1857, Mendel deduced that heritable factors, which we now call genes, govern various physical traits displayed by the species.  Prior to the work of Gregor Mendel, a late-19th- century monk, scientists thought that inheritance was a blending process in which the properties of the sperm and the egg simply mixed, much as one might mix two colors of paint Mendel demonstrated that inheritance occurs Mendelian Genetics through genes, units of heredity that maintain their structural identity from one generation to another. As a rule, genes come in pairs because they are aligned along chromosomes (strands of genes), which also come in pairs  A gene is a portion of a chromosome, which is composed of the double-stranded molecule deoxyribonucleic acid (DNA). A strand of DNA serves as a template (model) for Mendelian Genetics the synthesis of ribonucleic acid (RNA) molecules. RNA is a single-strand chemical; one type of RNA molecule serves as a template for the synthesis of protein molecules  Some proteins form part of the structure of the body; others serve as enzymes, biological catalysts that regulate chemical reactions in the body. Anyone with an identical pair of genes on the two chromosomes is homozygous for that gene. An individual with an unmatched pair of genes is Mendelian Genetics heterozygous for that gene. For example, you might have a gene for blue eyes on one chromosome and a gene for brown eyes on the other. Certain genes are dominant or recessive. A dominant gene shows a strong effect in either the homozygous or heterozygous condition; a recessive gene shows its effects only in the homozygous condition.  For example, someone with a gene for brown eyes (dominant) and one for blue eyes (recessive) has brown eyes but is a “carrier” for the blue-eye gene and can transmit it to a child. Mendelian Genetics For a behavioral example, the gene for ability to taste moderate concentrations of phenylthiocarbamide (PTC) is dominant; the gene for low sensitivity is recessive. Only someone with two recessive genes has trouble tasting it  Most traits are controlled by multiple genes, but some traits are controlled by one gene. A characteristic like cleft chin, for example, is influenced by a single gene from each parent. In this example, we will call the gene for cleft chin “B,” and the gene for smooth chin “b.” Cleft chin is a dominant trait, which means that having Genetics the dominant allele either from one parent (Bb) or both parents (BB) will always result in the phenotype associated with the dominant allele. When someone has two copies of the same allele, they are said to be homozygous for that allele. When someone has a combination of alleles for a given gene, they are said to be heterozygous. For example, smooth chin is a recessive trait, which means that an individual will only display the smooth chin phenotype if they are homozygous for that recessive allele (bb).  Imagine that a person with a cleft chin Genetics mates with a person with a smooth chin. What type of chin will their offspring have?  The answer to that depends on which alleles each parent carries. If the person with a cleft is homozygous for cleft chin (BB), their offspring will always have cleft chin. It gets a little more complicated, however, if the person is Genetics heterozygous for this gene (Bb). Since the other person has a smooth chin—therefore homozygous for the recessive allele (bb)—we can expect the offspring to have a 50% chance of having a cleft chin and a 50% chance of having a smooth chin  The principles of inheritance that Mendel demonstrated through his experiments have led to countless discoveries about genetics. We now know that new traits appear because new gene combinations are inherited from parents and that genes change or mutate. Heredity and But genes alone cannot explain most traits. Even Mendel realized environment that the environment participates in the expression of traits; for example, planting tall peas in poor soil reduces their height. The experience likewise plays a part. The experience of children who attend a substandard school, for instance, is different from that of children who attend a model school.  We now know that genes and their effects are not static; genes can be active at different times and under different conditions during our life. The field of epigenetics (meaning “beyond genes”) studies how gene expression is turned on or off at different times and how environment and experience influence our behavior through their Heredity and effects on our genes environment Epigenetic factors consist of a number of biochemical changes that influence whether a gene is active or inactive. Epigenetic factors can turn on or turn off a gene’s function so that the gene influences the function of our body or behavior, or it stops that influence. The epigenetic effects of experience that initiate epigenetic influences on genes can last long after the initial experience and, in some cases, can persist into future generations.  Unlike PTC sensitivity and color vision deficiency, most variations in behavior depend on the combined influence of many genes and environment. You may occasionally hear someone ask about a behavior, “Which is more important, heredity or environment?” That question as Heredity and stated is meaningless. environment Every behavior requires both heredity and environment. However, we can rephrase it meaningfully: Do the observed differences among individuals depend more on differences in heredity or differences in environment? For example, if you sing better than I do, the reason could be that you have different genes, that you had better training, or both  To determine the contributions of heredity and environment, researchers rely mainly on two kinds of evidence. First, they compare monozygotic (“from one egg,” i.e., identical) twins and dizygotic (“from two eggs,” i.e., fraternal) twins. Heredity and A stronger resemblance between monozygotic than dizygotic twins environment suggests a genetic contribution. Second, researchers examine adopted children. Any tendency for adopted children to resemble their biological parents suggests a hereditary influence. If the variations in some characteristic depend largely on hereditary influences, the characteristic has high heritability  Humans are difficult research animals. Investigators cannot control people’s heredity or environment, and even their best methods of estimating hereditary influences are subject to error. Another complication: Certain environmental factors can inactivate a gene by attaching a methyl group (CH3) to it. In some cases, an Heredity and early experience such as malnutrition or severe stress inactivates a environment gene, and then the individual passes on the inactivated gene to (Possible the next generation. comlpications) Genes can also influence your behavior indirectly by changing your environment. For example, suppose your genes lead you to frequent temper tantrums. Other people—including your parents—will react harshly, giving you still further reason to feel hostile  Even a trait with a strong hereditary influence can be modified by environmental interventions. For a human example, phenylketonuria (FEE-nilKEET-uhn-YOOR- ee-uh), or PKU, is a genetic inability to metabolize the amino acid phenylalanine. If PKU is not treated, the phenylalanine accumulates to toxic levels, impairing brain development and Environmental leaving children mentally retarded, restless, and irritable. modifications Approximately 1% of Europeans carry a recessive gene for PKU; fewer Asians and almost no Africans have the gene Although PKU is a hereditary condition, environmental interventions can modify it. Physicians in many countries routinely measure the level of phenylalanine or its metabolites in babies’ blood or urine. If a baby has high levels, indicating PKU, physicians advise the parents to put the baby on a strict low-phenylalanine diet to minimize brain damage Question What example illustrates the point that even if some characteristic is highly heritable, a change in the environment can alter it? THANK YOU Likitha S Department of Psychology [email protected]