Researchers study mutations in developmental disorders using many different techniques, many of which involve animal models. In animal models, researchers may be able to perform the following: 

-Site-directed mutagenesis: Researchers mutate a specific gene using this technique.

-Knockout organism: When site-directed mutagenesis has been performed to completely remove a gene, the organism is called a knock-out organism. We cannot always assume that a lack of behavioral changes to a knockout organism means that the gene that has been knocked out is not important to that behavior! 

-Transgenic organism: An organism whose genetic material has been altered by the addition of a gene that is new or somehow modified. This is particularly useful for studying genetic disorders.

Some of these methods can be applied later in an animal's lifespan to deduce the effect of mutations in an adult organism. 

Studying Mutations in Developmental Disorders

Clones are organisms that are genetically identical, and are formed via asexual reproduction. They can provide insight as to the relative influence of genetics and the environment in sculpting a particular behavior. 

Clones

- As  certain species reproduce, there will be some level of variation caused by mutations
- Mutations that are advantageous to survival (known as "adaptive mutations") wil become more common within a species, and passed down to subsequent generations

Adaptive Mutations 

A population of bacteria is exposed to a powerful antibiotic, which kills most of the cells. However, a small number of bacteria survive because they possess a sudden, permanent change in one of their genes that was not present in the parent population. Based on this information, what is the most accurate conclusion to draw about this genetic change?

A mutation is a sudden, permanent change in a sequence of DNA. Mutations serve as a primary source for harmful genes, such as the one causing Phenylketonuria (PKU). While many mutations can be detrimental or lethal, they can occasionally be beneficial, conferring an advantage to an individual that enhances their survival and reproductive success compared to others.

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Brandeis University

Phenylketonuria (PKU) is a recessive hereditary disorder, meaning that two copies of the mutated gene implicated in PKU disease processes must be inherited in order for an individual to display symptoms of this disorder. It’s one of the most common inherited metabolic disorders. The mutated genes cannot produce the enzyme that normally metabolizes the compound phenylalanine, found in certain food products, into tyrosine. The build-up of phenylalanine in the brain can become toxic, leading to intellectual disability when the build-up interferes with myelination in the central nervous system. If a baby with PKU ingests food with phenylalanine, the build-up during the post-birh period stunts brain development. Because of its preventable nature, and because the test is inexpensive and accurate, many governments have passed laws for mandatory PKU testing shortly after birth, and this has prevented many cases of intellectual disability.
PKU can be prevented by regulating the level of phenylalanine intake, especially early in life. After the post-birth brain development period has passed, the low phenylalanine diet can be relaxed somewhat since the danger to brain development has passed. 
For pregnant women with PKU, however, this isn’t the case. When a fetus is in utero, it’s protected by its mother’s metabolism. For non-PKU having mothers, this means the baby is especially protected during this time. However, if the mother has PKU and ingests a diet with typical or high levels of phenylalanine - while it won’t damage HER brain - it will cause improper brain development in the fetus. 

Phenylketonuria (PKU)

Genes are specific sequences of DNA that provide the code for particular traits. These traits can be both physical and psychological characteristics, and their ultimate expression is determined by the interplay between genetics and environmental factors.

Genes

Breedlove, S. & Watson, N. (2017). Behavioral neuroscience, eighth edition. Oxford University Press.

Behavioral Neuroscience 8th Edition

Spielman, R. M., Jenkins, W. J., & Lovett, M. D. (2020, April 22). Psychology (2nd ed.). OpenStax. https://openstax.org/books/psychology-2e/pages/1-introduction

OpenStax Psychology (2nd ed.) Textbook

Carlson, N. and Birkett, M., 2017. Physiology of Behavior. 12th ed. Pearson.

Physiology of Behavior

Mutation

- Coiled lengths of DNA that contain genes
- Found within the cell nucleus 

Chromosome

- Nuclear Receptor Subfamily 3 Group C Member 1 (NR3C1) encodes glucocorticoid receptor.
   - Can function as a transcription factor that binds to glucocorticoid response elements in the promoters of glucocorticoid responsive genes to activate their transcription.
    - Can function as a regulator of other transcription factors.
- It is involved in inflammatory responses, cellular proliferation, and differentiation in target tissues.
- Mutations in this gene are associated with generalized glucocorticoid resistance.

NR3C1 Gene

The manipulation of genetic material, by replacing defective genes or introducing new genes, to treat or prevent disease. Vectors are used to transport DNA into cells.

Gene therapy

Polygenic refers to traits that are controlled by multiple genes (i.e. height, skin color, weight). 

Polygenic

Traits are characteristics of an individual that are at least partially controlled by genes. While commonly associated with observable physical attributes like eye or hair color, the concept of traits also extends to non-physical characteristics, including behavioral patterns, personality, and temperament. The complete set of an individual's observable traits, both physical and behavioral, constitutes their phenotype.

Traits

Two identical twins, who share the exact same genetic makeup, were separated at birth and raised in significantly different environments. As adults, Twin A is outgoing and confident, while Twin B is shy and anxious. Based on the modern understanding of how genes influence traits, what is the most likely explanation for this difference in their psychological characteristics?

Using your understanding of how genetic and environmental factors interact, explain the most likely reason for the different psychological outcomes in the following scenario.

Analysis of Twin Outcomes

An allele is a specific version or variation of a gene. While a single gene may provide the code for a general trait, such as hair color, the different alleles of that gene determine the specific variation of the trait that an individual expresses.

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