1. Genotypes and Phenotypes
Gene Expression
Factors that Affect Gene Expression

2.  Human diseases are caused by a multitude of genetic
and environmental factors acting together.
 In certain conditions such as Down syndrome, genetic
factors predominate, while in infectious diseases, for
example, environmental factors predominate.
 Most chronic non-communicable diseases such as
schizophrenia and diabetes, asthma, obesity,
coronary artery disease as well as some congenital
malformations are caused by an interaction of both
genetic and environmental factors.

3.  Diseases that show familial clustering but do
not conform to any recognized pattern of
single gene inheritance are termed
multifactorial disorders.
 They are determined by the additive effects of
many genes at different loci together with the
effect of environmental factors.

5.  What is Mendelian genetics?
Mendelian way of inheritance(dominant, recessive
or sex-linked) is the way most of us studied
genetics in college.
Mendelian genetics applies to rare diseases only,
such as cystic fibrosis, Huntington’s disease,
muscular dystrophies, etc.
These conditions render individuals unfit for
breeding, which is the reason they are rare.

7.  Common diseases such as diabetes mellitus type 2, asthma, coronary artery
disease or schizophrenia are called complex diseases and their inheritance is
multifactorial.
 Multifactorial Diseases can be detected by association studies.
 Monogenic diseases are usually detected by linkage studies.

8.  A high probability(p) of a genetic locus being associated with
a condition(red bars)- in this example EGR3 gene signals the
highest ( p )value.

9.  These conditions show a definite familial
tendency but the incidence in close relatives
of affected individuals is usually around 2-4%
instead of the much higher figures that would
be seen if these conditions were caused by
mutations in single genes(25-50%).

11. Congenital Malformations:
-Congenital heart defects
-Neural tube defects
-Cleft lip/palate
-Pyloric stenosis
-Congenital hip displasia
Common non-communicable diseases:
-Asthma
-Schizophrenia
-Diabetes Mellitus
-Hypertension

12.  Genes code for proteins.
 Proteins determine the visible characteristic of an individual
(phenotype).

15. The inheritance and expression of a phenotype is determined by many genes
at different loci, with each gene exerting a small additive effect.
 Additive implies that the effects of the genes are cumulative, i.e. no one gene
is dominant or recessive to another.

16.  Multiple genes and the environment lead to vulnerability for the
schizophrenia phenotype.

17.  Genes do not cause schizophrenia or symptoms of schizophrenia.
 Genes cause subtle molecular changes in proteins and cells that may bias the
individual towards psychosis.
 Genes do not respect the boundaries between schizophrenia, bipolar
disorder or dementia.

18.  Enlarged lateral ventricles is a frequent endophenotype in
schizophrenia.

19.  Heritability of a trait or disease is the
proportion of the total variance that is
genetic.
 The overall variance of the phenotype is the
sum of the environmental and genetic
variance.
 Heritability provides information of the
importance of genetic factors in the causation
of a disease.

20.  Schizophrenia 85
 Asthma 80
 Pyloric stenosis 75
 Ischemic heart disease 65
 Essential hypertension 60
 Spina bifida 60
 Diabetes mellitus 40