Genetics of Common Diseases Flashcards
true or false: both genetic and environmental factors are both involved in common disorders.
true
synonyms for common diseases
complex
multifactorial chronic
common idseases are the result of multiple factors
genetic epigenetic
environmental
true or false: common diseases are usually not caused by a single gene.
true
do common diseases have a simple medelian pattern of inheritance?
no
do common diseases run in families?
yes
common diseases are _ both in phenotype and genotype
heterogeneous
susceptibility genes
genes involved in common diseases. They contribute to risk of developing a disease but are not enough to cause the disease.
complex diseases (genes and frequency)
high frequency, low genetic distribution, variable penetrance
mendelian diseases (genes and frequency)
low frequency, high genetic distribution, high penetrance
how to distinguish genetic and environmental factors
study concordance and discordance of disease in twins: identical and fraternal
twins: identical - reared together and apart
adopted individuals: birth parents and adopted parents.
when both twins in a family have the same disease phenotype, they are _ for the disease.
concordant
when only one pair of member of twins is affected and the other is not,, the twins are _ for the disease.
discordant
heritability
the proportion of phenotypic variation in a trait that is due to underlying genetic variation.
e.g. The heritability of ADHD is 80% means genetic factors are strongly involved in causing symptoms of ADHD.
monozygotic twins
identical twins with identical genotypes, but mitochondrial genomes could be different.
dizygotic twins
arise from the simulatneous fertilization of two eggs by two sperm and share 50% of alleles.
disease concordance of less than 100% in MZ twins suggests that _ play a role in disease
nongenetic factors play a role in disease.
what is discordance usually a result of?
environmental influences
epigenetic differences
greater concordance in _ vs. _ twins is strong evidence of a strong genetic component to the disease.
greater concordance in MZ vs DZ twins is strong evidence of a strong genetic component to the disease.
what do studies of MZ twin pairs reared apart show?
that shared genetic factors are more important than shared environmental factors for many common diseases.
adoption studies
compaire similarity for a trait or disorder in biological versus adoptive rleatives to determine the degree to which genetic and shared environmental factors contibue to a phenotype.
common variants
genes involved in a disorder in which the minor allele presents in a frequency of 1 - 5%. They have low penetrance.
rare variants
multiple rare DNA variants with high penetrance.
Common disease, rare variant
a proportion of inherited susceptibility to relatively common human chronic diseases may be due to the summation of the effects of low frequency and independently acting variants.
They are less than 1% and can be identified only by sequencing.
Genome wide association studies
Studies designed to identify the genetic variation in common diseases. It is based on the idea that comon variants are involved.
it involves comparing allele frequencies hundreds of thousands of common variants spread across the genome between large samples of patients and control cases.
SNP alleles more frequent with people with the disease are said to be _ with the disease.
associated
In GWAs, associated SNPs are
considered as pointers to the region of the human genome where the disease causing genes are likely to reside. The SNP itself is not necessarily involved but is close to the loci that are involved.
What GWA does not require
any hypothesis about what gene or genes one is looking for.
No assumption about the function of the genes are required or its chromosomal location.
What the GWA requires
large numbers of affected individuals and control individuals - populations, not families.
What is examined in GWA
millions of common SNPs spread across the entire genome using microarray chips.
features of common diseases
They are usually not caused by mutations in a single gene.
Common diseases tend to run in families, and individuals do not always develop a common disease due to the presence of faulty genes.
