Genes and behaviour Flashcards
Explain one study of how genes influence one behaviour
Epigenetic’s is the study of how behavior and the environment can change gene expression. This establishes whether genes are responsible for a particular behavior. Diathesis-stress theories of depression predict that an individual’s reaction to stressful events depends on their genetic make-up. If an individual has a specific genotype, then interaction with the environment may cause these genes to be expressed. The aim of Caspi’s study was to determine whether there is evidence for a gene-environment interaction (G x E) for a mutation of the serotonin transporter gene - 5-HTT. The serotonin transporter is involved in the reuptake of serotonin in brain synapses. Methods used in molecular genetics help identify specific genes responsible for specific behaviors. One such example is the 5-HTT gene which is believed to be responsible for modulating the reaction to stressful life events.
The aim of Caspi et als (2003) study was to investigate the role of the 5-HTT gene in developing depression in response to stressful life events. It was a longitudinal study. Genetic mapping was used to divide participants into three groups: both short alleles of 5-HTT, one short allele and one long allele, and both long alleles. Participants were assessed through the ages 3 and 26. Two measures were used: a “life history calendar” to assess stressful life events and an interview to assess symptoms of depression. Participants who had one or two short alleles of 5-HTT (s/l and especially s/s) reacted to stressful life events with more depressive symptoms. For example, participants who has a major stressful life event at age 21 tended to develop depression by age 26, but only if they carried a short allele of 5-HTT.
It was concluded that the 5-HTT gene is responsible for modulating an individual’s vulnerability to stress. The 5-HTT gene doesn’t means people with the short allele are more likely to develop depression as the short allele is not enough, rather it means that people with the short allele react to stressful life events in a way that may cause depression. People who have the short allele showed more depressive symptoms when reacting to stress which then may lead to depression. Epigenetic’s changed the gene expression as people who expressed multiple stressful events were more likely to develop depression. This links to the diathesis stress model as it insinuates the some people are more perceptible to inheriting mental disorders based on their genes, therefore if someone possesses the one or more short allele of 5-HTT gene they are likely to experience a mental disorder after a stressful life event. This tells us that genes are closely linked with the behavior that we may experience throughout our life as they influence what we are more perceptible to.
Explain the use of one twin to kinship study to investigate one human behaviour
Twin studies are studies conducted on identical (MZ) or fraternal (DZ) twins. Twin studies allow us to estimate how much a trait comes from out genes and how much it comes from our environment as we can neglect the influence of nature. Monozygotic twins are identical and share 100% of their genes and environment, however dizygotic twins only share 50% of the genes but 100% of the environment. Shared environment assumes that those living in the same family are experiencing the same environment however the issue with this is that it isn’t accurate, however non-shared means that there are subjectively different ways in which parents treat each child, even one of identical twins, and there are also objectively different ways in which even identical treatment is perceived by each individual child. This is interesting for psychologists as it may effect certain traits for example a shared environment is important for traits like general intelligence. This is important as it shows how similar the nature is between the twins as researchers can see how much of their environment was shared. One study that demonstrates this is McGuffin.
The aim of the study was to estimate the contribution of genes and shared family environment on the tendency to having major depressive disorder, and to examine influence of characteristic of one twin suffering from the disorder on the likelihood of the other suffering from it. This was a study of 177 twins and same-sex- co-twins. One twin was usually interviewed by a different researcher than was the other. The pro bands and their co-twins were asked about their shared environment: whether they were still in regular contact; for how long they had lived together, and whether they had shared a bedroom, and, if so, for how long. They were also asked to degree to which, as children, friends and parents treated them alike. The aim here was to examine the equal environments assumptions, that MZ and DZ twins share the family environment to an approximately similar extent. Correlations in the presence or absence of depression in the co-twin were calculated. The results were as follows: The concordance rate of major depressive disorder for MZ twins was 46% and for non-identical(DZ) twins was 20%. Durations of depressive episodes that were less than 13 months were correlated more strongly with depression in the other twin. When the researchers compare the incidence of depression and the identical twins at aged 65 years with the expected incidence of depression in the general population at that age, they found that the heritability factor rose to 70%.
McGuffin concluded that there is a strong genetic component to major depressive disorder, and no evidence for it being caused by a shared family environment. A shorter duration of a major depressive episode in one twin increase the likelihood of the other twin being a sufferer, suggesting that this was one criterion for higher genetic component. The understanding couldn’t have been achieved without research into twins as they were able to separate out the influences of nature and nurture by comparing the resemblance between identical twins with the resemblance between non-identical twins. This explains why there is a higher concordance rate for MZ twins as they share more of their genetic material. They used twins as they can compare the results to determine whether it is due to an environmental or genetic factor. This is because they could compare the results of identical twins to non identical twins which theoretically only have a difference in shared genes and not environment. The concordance rate of the DZ twins was evidence that major depressive disorder was due to genetics as compared to the MZ twins there was only a genetic difference as they shared 100% of their environment.
Explain one evolutionary explanation of one behaviour
Sociobiology has extended its theoretical basis to incorporate the idea of sulfured evolution and the interaction it might have with genetic evolution. Sexual selection occurs as a desultory of different levels of parental investment between males and females. In humans, it is the female who biologically invests more than the male. There are a few reasons for this: the first is anisogamy which means that female invest in producing relatively few, large, long lasting and energy rich gametes while men produce many, short lived and rapidly renewable gametes. Another explanation is that females provide more resources for developing the zygote and they produce milk got offsprings nutrition. The female always knows that the offspring are hers whereas the male does not get this garnered, this is called parental certainty. Lastly, females are more likely to continue caring for offspring after birth compared to males .Clarke and Hatfield’s aim was to investigate the difference in choosiness shown by males and females when approached by a stranger offering sex.
The method was as follows: the study was carried out in two different years using an opportunity sample of 48 female and 48 male Florida University students. Five female and four male confederates were instructed to place themselves at one of the five pre-determined points around the university campus. The confederated were approximately 22 years old; similar to the ages of students participants that they would be approaching. Each confederate approached an opposite-sex lone participant and at random made one of the following pre-determined requests:
‘I’ve watched you around campus, I find you very attractive’ followed by either:
‘Would you go out with me tonight?’ Or ‘would you come over to my apartment tonight?’ Or ‘would you go to bed with me tonight?’
The confederates were instructed to only approach participants whom they found genuinely attractive and with whom they would actually consider having sex. The results were that the request for a date was met with around 50% agreement from both men and woman. However 75% and 69% of males said ‘yes’ to having sex with the confederate compared to 0% of the woman in both studies. In other words, around thee-quarters of the makes participants were willing to have sex with a stranger; non of the woman were.
They concluded that woman do appear to operate a system of increased choosiness when it comes to their sexual behavior, whereas men seem to be less bothered by a possibly risky sexual encounter with a stranger. This supports the evolutionary theory of mate selection. Males are biologically less choosy as they invest less when producing offspring. When looking for a female males tend to look for someone young and someone who possesses an ‘hour-glass’ figure as this means they possess wider hips which makes pregnancy and childbirth easier. Males look for healthier looking females as they are more likely to have better genes and they invest more biologically so they need to be healthy to be able to raise a healthy child. Females are biologically more choosy as they invest more when producing offspring. Females tend to look for males who have status and dominance as this shows that they can provide for them, these men tend to be older. Females also look for males who posses promising qualities such as drive ambition, intelligence and skill, as well as physical health from things such as size and musculature and commitment of resources through pre-mating signs of kindness and generosity. Therefore, both genders look for the optimal genes for a partner of the opposite sex to be able to reproduce and pass on strong genes.
Outline the study used in the question ‘Explain one study of how genes influence one behaviour’
The aim of Caspi et als (2003) study was to investigate the role of the 5-HTT gene in developing depression in response to stressful life events. It was a longitudinal study with 1037 participants from New Zealand. Genetic mapping was used to divide participants into three groups: both short alleles of 5-HTT, one short allele and one long allele, and both long alleles. Participants were assessed through the ages 3 and 26. Two measures were used: a “life history calendar” to assess stressful life events and an interview to assess symptoms of depression. Participants who had one or two short alleles of 5-HTT (s/l and especially s/s) reacted to stressful life events with more depressive symptoms. For example, participants who has a major stressful life event at age 21 tended to develop depression by age 26, but only if they carried a short allele of 5-HTT.
Outline the study used in the question ‘Explain the use of one twin to kinship study to investigate one human behaviour’
The aim of McGuffin’s study was to estimate the contribution of genes and shared family environment on the tendency to having major depressive disorder, and to examine influence of characteristic of one twin suffering from the disorder on the likelihood of the other suffering from it. This was a study of 177 twins and same-sex-co-twins. One twin was usually interviewed by a different researcher than was the other. The pro bands and their co-twins were asked about their shared environment: whether they were still in regular contact; for how long they had lived together, and whether they had shared a bedroom, and, if so, for how long. They were also asked to degree to which, as children, friends and parents treated them alike. The aim here was to examine the equal environments assumptions, that MZ and DZ twins share the family environment to an approximately similar extent. Correlations in the presence or absence of depression in the co-twin were calculated. The results were as follows: The concordance rate of major depressive disorder for MZ twins was 46% and for non-identical(DZ) twins was 20%. Durations of depressive episodes that were less than 13 months were correlated more strongly with depression in the other twin. When the researchers compare the incidence of depression and the identical twins at aged 65 years with the expected incidence of depression in the general population at that age, they found that the heritability factor rose to 70%.
Outline the study used in ‘Explain one evolutionary explanation of one behaviour’
Clarke and Hatfield’s aim was to investigate the difference in choosiness shown by males and females when approached by a stranger offering sex. The method was as follows: the study was carried out in two different years using an opportunity sample of 48 female and 48 male Florida University students. Five female and four male confederates were instructed to place themselves at one of the five pre-determined points around the university campus. The confederated were approximately 22 years old; similar to the ages of students participants that they would be approaching. Each confederate approached an opposite-sex lone participant and at random made one of the following pre-determined requests:
‘I’ve watched you around campus, I find you very attractive’ followed by either:
‘Would you go out with me tonight?’ Or ‘would you come over to my apartment tonight?’ Or ‘would you go to bed with me tonight?’
The confederates were instructed to only approach participants whom they found genuinely attractive and with whom they would actually consider having sex.The results were that the request for a date was met with around 50% agreement from both men and woman. However 75% and 69% of males said ‘yes’ to having sex with the confederate compared to 0% of the woman in both studies. In other words, around thee-quarters of the male participants were willing to have sex with a stranger; non of the woman were.
