What does it mean when someone is genetically predisposed to something?

 Genetic Vulnerabilities

Genes are long molecules of DNA present on chromosomes within a cell nucleus. Genes carry the information we inherit from our parents and exist in alternate forms called alleles. Most mental disorders show some genetic influence, with some influences apparent in newborns and children, while others manifest in adolescence or adulthood. Each human cell has 23 pairs of chromosomes containing genetic materials that encode the hereditary plan for each individual. One copy of each chromosome comes from the mother and one from the father. Twenty-two chromosome pairs determine an individual’s general characteristics, while the remaining pair, the sex chromosomes, determines the individual’s sex (Hooley et al, 2019).

(Hooley et al, 2019)

Abnormalities in the structure or number of chromosomes can be associated with major defects or disorders. Anomalies may also occur in the sex chromosomes, producing complications that may predispose a person to develop abnormal behavior.

Polymorphisms are naturally occurring variations of genes. Polymorphisms often influence personality traits. The term polygenic means influenced by multiple genes or polymorphisms of genes. 

When we say someone is genetically vulnerable we are saying that they have inherited a large number of genes or polymorphisms of genes that can work together to make someone more susceptible to developing a mental disorder. 

 These genes may cause abnormal structures in the central nervous system, and abnormal regulation of brain chemistry, and hormone levels. This can also alter the reactivity of the autonomic nervous system.

Keep in mind that behavior is not determined by genetics alone. Our interaction with the environment along with genetics determines our behavior.

Stress which can be caused by environmental factors can actually activate or deactivate gene expression. 

Genotype

is a term used to describe the genetic makeup of an individual. It is the
complete set of genes that an individual inherits from their parents. 

Genetic endowment 

is another term for genotype. It refers to the genes that an individual has, regardless of whether or not they are expressed in their phenotype.

Phenotype

Is the structural and functional characteristics that result from the interaction of someone's genotype and the environment,

The interaction of genotype and environment is complex and can vary from one individual to another. However, it is important to understand that phenotype is not simply determined by genotype. The environment plays an important role in shaping our physical and functional characteristics.

References

 Hooley, J. M., Nock, M. K., & Butcher, J. N. (2019). Abnormal Psychology (18th ed.). Pearson Education (US). https://bookshelf.vitalsource.com/books/9780135191033