Pearson BTEC National Applied Psychology Book 1

B4 Biological approach Key concepts: ● The influence of biology on behaviour. ● Genes, including the role of genotype, phenotype and the SRY gene. Specification content Given what you have read on this spread, how do you think psychologists use genes in their explanations of behaviour? An issue to consider W e have seen that genetically identical twins are not identical in their behaviour or even their appearance (even their fingerprints are different). This is why we make a very important distinction between genotype and phenotype. For example, the ability to taste phenylthiocarbamide (PTC), a bitter- tasting chemical) in food is genetically controlled by a single gene. But even people in whom the gene is ‘switched on’ will not always taste it. 1. How can the concepts of genotype and phenotype explain this? 2. What environmental factors could influence the genotype? ACTIVE GET Evaluation An interactionist approach One strength of understanding genotype and phenotype is that these concepts support interactionism in psychology. For example, one version of the BRCA gene has been linked to breast cancer risk in women. But not every woman who has this version of the BRCA gene develops breast cancer, so clearly other factors (e.g. stress) interact with the genotype to produce the observable outcome (phenotype). Taking into account the interactions between nature and nurture provides a much fuller and richer explanation of human behaviour. Risk of oversimpli cation One weakness is that some research oversimpli es the in uence of genes. It is very rare that only one gene determines a behaviour. We talk about one version of the BRCA gene causing cancer but what it causes is an increased risk. Not everyone with the abnormal version develops cancer. The same is true for ‘a gene for depression’ or ‘a gene for blue eyes’. This is not an accurate view of how genes operate. No human behaviours are caused by single genes. Instead, many genes (sometimes hundreds or thousands) make small but important contributions in complex interactions with each other. Also genes do not produce effects in isolation. They interact with environmental in uences to produce a phenotype. The danger is that oversimpli ed explanations of how genes work exaggerate the role of nature and present a misleading view of the causes of behaviour. Content area B4: Biological approach Introduction and key concept 1 Specification terms Genes A unit of inheritance. They consist of chemical instructions (DNA) which tell your body what proteins to manufacture – and basically that is what you are, a huge number of proteins. Genes are inherited from parents and contribute to the development of an individual’s characteristics. Genotype An individual’s total set of genes. Phenotype The observable characteristics which result from the interaction between a person’s genotype and environmental factors. SRY gene Sex-determining region Y gene which triggers the appearance of testes in an embryo and the development of that individual into a biological male. How identical is identical? Psychologists call twins identical because they have exactly the same genes. Most people use the word in everyday language to mean that twins look identical. But do they really? Look more closely and you will see that even the most ‘ identical ’ of twins look a bit di erent. Things get even more interesting when you consider behaviour. Even identical twins who have been brought up together in the same home do not behave identically. For instance one might be gay and the other straight. One becomes a scientist, the other an artist. What this tells us is that, even if you had an identical twin, there will never be someone exactly like you. Your experiences and your environment will a ect you in di erent ways to make you the person you are. It ’ s not ‘ all in the genes ’ . Influence of biology on behaviour Biology and behaviour Biological structures and processes within the body have a profound effect on our psychological functioning and behaviour. Biological psychologists argue that, as the mind basically ‘lives’ in the brain, our thoughts, feelings and behaviour have a physical basis (everything psychological is rst biological). There are several biological in uences we look at on the next few spreads. They all vary slightly between males and females, leading to some sex differences in behaviour. • Genes are described below. • Neuroanatomy refers to the structure of the nervous system, including the brain. Different parts of the structure have different functions such as one area controls what we see (the visual area) and another area controls movement (the motor area). • Neurochemistry concerns the chemical processes that occur within the brain and nervous system. Messages are sent around the brain and body via nerves (also called neurons ) but also via chemical messengers (neurotransmitters) . • Evolution concerns the way animals change over millions of years. At one time the only life on Planet Earth was small one-celled organisms. Over time these life forms have evolved into all the species you see around us today. The process of evolution explains how this happened. Key concept: Genes What are genes? Genes are located on chromosomes and humans have 46 chromosomes (23 pairs). Each gene is made up of strands of DNA (deoxyribonucleic acid). Genes carry ‘instructions’ relating to the physical and non-physical characteristics of living organisms, such as the colour of your hair and whether you have a calm temperament. Typically each individual inherits two copies (called alleles ) of every gene, one from each parent. Genotype and phenotype Genotype refers to an individual’s actual genetic make-up. It is what you inherit from your parents. However, your genotype doesn’t determine your physical and non-physical characteristics directly because the genes have to be expressed through an interaction with your ‘environment’. Even within your body the environment has an in uence, for example the food you eat affects your body’s internal environment. A person’s phenotype is how their genes are actually expressed. A phenotype is therefore an interaction of genotype and environmental in uences. Identical twins have the same genotype because they have inherited exactly the same genes. But the expression of their genes (phenotype) differs. They may look physically different because, for example one twin goes to the gym and the other doesn’t and therefore one twin has developed bigger muscles. The other twin might develop bigger muscles too – but only if their environment changed. The distinction between genotype and phenotype strongly suggests that most human behaviours are due to an interaction of inherited (nature) and environmental (nurture) factors. The SRY gene One pair of chromosomes determines biological sex – XX for female, XY for male. The so-called Y-chromosome is in reality just a stunted X-chromosome, missing some of the genetic material. Located on the Y chromosome is a gene called the sex-determining region Y gene ( SRY gene). In typical development before birth, the SRY gene switches on other genes causing an XY embryo to develop testes. In adult males the testes produce sperm but during development the testes produce male sex hormones and these hormones cause the embryo to become biologically male. Without the SRY gene, other genes remain switched off so the embryo develops into a female. A gene is actually just a stretch of chemicals located on a strand of DNA. For example, the area highlighted in yellow could represent one gene on a long twisted strand. These strands are further coiled and make up chromosomes. Chromosomes typically come in pairs (one from your mother and one from your father) and are shaped vaguely like an X. The chromosome on the le is an X chromosome and on the right is a Y chromosome. They are called X and Y because they resemble the shape of these letters. This photograph was taken using a very high-powered microscope. 1. State what is meant by the term ‘genes’. (1) 2. Using at least one example, explain how biology in uences behaviour. (3) 3. Explain one difference between genotype and phenotype. (2) 4. Describe how the SRY gene in uences behaviour. (3) 5. Wanda is pregnant and having her second ultrasound scan (at 20 weeks). She wants to know the biological sex of the baby. ‘It’s a boy,’ the doctor tells her. Explain how a biological psychologist might account for the biological sex of a baby. Use the concept of genes in your answer. (3) 6. Phenylketonuria (PKU) is a rare genetic disorder that can cause severe learning difficulties, seizures and behavioural problems. However, it is relatively easy to detect in newborn babies. A baby with PKU placed on a low-protein diet is very likely to develop normally and never experience symptoms. Evaluate the in uence of genes on behaviour with reference to this scenario. In your answer you should consider the roles of genotype and phenotype, and relate this to PKU. (9) Exam-style questions According to biological psychologists, everything that is psychological is rst biological, most notably the brain. Our thoughts, feelings and behaviours are all controlled from this mighty organ. The brain itself is created from the instructions encoded in genes. 30 31 Unit 1: Psychological approaches and applications