GENETIC RESEARCH METHODS IN SCHIZOPHRENIA

.

Scientists use specialised methods to explore the links between genes and individual differences. Many different research methods are used to test genetic theories, which I have detailed below, but first, ensure you understand the following key terms.

KEYWORDS

GENOTYPE:

• The genes on the 23 pairs of human chromosomes represent a person's genetic makeup.

• A genotype never changes; phenotype can change over time.

• An example to illustrate the difference between them.

  About intelligence, they may explain that an individual might have an intellectual potential (genotype), but they require environmental stimulus such as education for this to develop.

  PKU is an example of a disorder caused by a defective gene resulting in severe learning difficulties. However, if identified early and treated with a special diet, individuals show normal levels of intelligence. Other examples, e.g., schizophrenia

PHENOTYPE:

Genetics and the environment determine a person’s actual/observable characteristics. e.g., physical appearance, behavioural characteristics, personality.

THERE ARE TWO TYPES OF TWINS:

• MONOZYGOTIC TWINS: MZ or Identical twins. Twins share the same genetic makeup because they develop from a single sperm fertilising a single egg to create a single zygote, which then divides into two separate embryos before continuing to grow. MZ twins have the same genotype / DNA.

• DIZYGOTIC TWINS: DZ twins: non-identical twins – or fraternal twins).DZ twins result from two different eggs being fertilised by two different sperm, resulting in two zygotes that grow in parallel. Non-identical twins are no more closely genetically related than any pair of full siblings (that is, sharing, on average, 50 per cent of the DNA that can differ between two people). However, they (conveniently for researchers) happen to be born simultaneously, so we do not need to worry about differences between twins within a pair due to age differences.

NON-EXPERIMENTAL RESEARCH METHODS OF THE GENETIC APPROACH

METHODS THAT ANALYSE THE FREQUENCY SCHIZOPHRENIA OCCURS IN FAMILIES.

• CONCORDANCE RATES:

  The percentage likelihood that if one individual in a pair has a trait, the other individual also has that trait.

• A PEDIGREE

  A pedigree is a genetic representation of a family tree that diagrams the inheritance of a trait or disease through several generations.

•  FAMILY STUDIES

  Investigate how much a characteristic runs in the family, e.g., the concordance/correlations of rates in 1st, 2nd, and 3rd-degree relatives (correlations essentially).

• TWIN STUDIES CONCORDANCE RATE OF TWINS -CORRELATIONS ESSENTIALLY

  Look at a particular characteristic in MZ twins raised together and compare it with DZ twins. If the characteristic has a higher concordance rate in MZ twins, it indicates a genetic basis. This indicates how much the characteristic is due to genetics. A characteristic that is 100% due to genetics (e.g., blood type) would have a 100% concordance rate in MZ twins.

  A very straightforward way to estimate the influence of genes is to compare DZ twins raised together with MZ twins raised together. The only thing that differs between the two types of twins is their DNA, so when MZ twins end up more like one another, DZ genes are inferred. If a trait were 100 per cent heritable, then MZ twins would be the same. If a trait were zero per cent heritable, then DZ would be no more like one another than MZ twins.

  In practice, we do not see either of these two extremes occurring. What is commonly referred to by behaviour geneticists as the "Heritability of Everything" paper (a meta-analysis, or systematic combination of available data, of twin studies across all outcomes) showed that the average correlation between identical twins was 0.6, and the average correlation between fraternal twins was 0.3. So, in neither group are the twins exactly alike (that would be a correlation of 1.0), nor are they entirely dissimilar (a correlation of 0.0). And, consistently across outcomes, identical twins are, on average, more like one another than non-identical twins.  All this together means that, across everything we have studied, heritability is not 100 per cent, but it is not zero per cent either.

• CONCORDANCE RATES OF SEPARATED MZ TWINS

  MZ twins might have high concordance rates because of their identical appearances. As a result, they might be treated as if they’re one person by many people. Separated MZ twin studies (and there are not many, as you can imagine) are conducted to separate environment and biology, e.g., nature and nurture, which was unclear from studies that looked at the concordance rates of MZ twins living together.

•  CHILDREN OF DISCONCORDANT MZ TWINS.

  Even separated MZ twins’ studies can’t rule out nurture. Looking at the offspring of the MZ twins who didn’t develop schizophrenia, but their MZ twin did (in other words, looking at MZ twins’ pairs who were dis-concordant for schizophrenia) might rule out nurture. It is very hard to conduct such studies because of the difficulties of obtaining such a niche sample.

•  OTHER METHODS: ADOPTION STUDIES

  Compare a trait or characteristic of an adopted child with their biological relative and adopted parents. This controls for environmental influences, separate environment, and biology, e.g., nature and nurture, was unclear from family studies. If a trait or characteristic is heritable, children should be more similar to their biological parents than adopted parents. If concordance/ correlation/similarity for adopted children is higher with natural parents than adopted parents, then the trait is biological.

EXPERIMENTAL RESEARCH METHODS OF THE GENETIC APPROACH

 Physiological techniques. Physiological techniques are directed at exploring the functional properties of organisms.

 GENE SEQUENCING SCHIZOPHRENIA

Use DNA analysis to investigate whether certain genes are associated with certain traits.

• Researchers use family histories. They compare DNA sequences of family members to identify genes involved in mental illness. First, they divide the family into two groups: affected and unaffected. Next, the researchers look for segments of chromosomes that are more common in affected people than unaffected ones. They narrow the segments down to specific genes to study further. Because people have complex and varied lives, in-depth studies are often done using animals in a controlled lab setting too.

• In recent years, genome-wide association studies (GWAS) have emerged as a major approach in behavioural genetics. A GWAS uses genetic testing to identify numerous genetic differences across many individuals and then analyse the association between these differences and personality traits or other outcomes.

•  Studies of twins who either do or do not have identical genomes allow for estimates of the degree to which genes drive the variation in psychological traits.

• Experimental breeding. Genetically diverse lines of organisms can be crossed in such a way to produce different behaviours.

• Cytogenetic techniques. Cytogenetics focuses on the microscopic examination of genetic components of the cell.

• ·Biochemical techniques. Biochemistry is carried out at the cellular or sub-cellular level, generally on cell extracts.