Multifactorial Inheritance Flashcards
what is the polygenic inheritance ?
Several genes located at
different loci contribute to the
etiology of the condition
disease.
example of polygenic and monogenic inheritance?
polygenic :
Diabetes mellitus
fingerprint ridge count
monogenic:
Sickle cell anemia is monogenic
what is the meaning of Multifactorial? With example ?
The effects of multiple genesInfluenced by and the pre- and postnatal environment .
height and skin color,
blood pressure, diabetes
Multifactorial follow or not for mendelian inheritance?
No
Multifactorial disorder can be categorized to ?
Congenital malformations
Acquired diseases of childhood and adult life
example of Congenital malformations?
Cleft lip/palate • Congenital heart defects • Neural tube defects (Spina bifida) • Pyloric stenosi
select the right disease for the right category?
Congenital malformations. Acquired diseases of childhood and adult life •
Cleft lip/palate Schizophrenia Cancer Manic depression Congenital heart defects Diabetes mellitus Neural tube defects (Spina bifida) Hypertension Ischaemic heart disease Epilepsy Diabetes mellitus Pyloric stenosis Asthma Autism
Congenital malformations. • • Cleft lip/palate • Congenital heart defects • Neural tube defects (Spina bifida) • Pyloric stenosis
Acquired diseases of childhood and adult life • Asthma • Autism • Epilepsy • Diabetes mellitus • Hypertension • Ischaemic heart disease • Manic depression • Schizophrenia
definition of Multigenic Inheritance ?
Caused by a number of genes at different loci which each have a small additive effect together with environmental factors
number of genes that affect height?
180
who is the control of the multigenic inheritance ?
single nucleotide polymorphisms ➢ These genetic polymorphisms all act
additively (80%). ➢ Plus interact with environmental factors
(Diet-protein, Vit D & A, calcium) to
determine final height (20%).
type of Multifactorial Traits? Example
continuous (or quantitative)
does not have a discreet phenotype e.G. Height, weight & blood pressure
Skin colour
Intelligence
discontinuous (qualitative) discreet phenotype such as diabetes and autism, left/ right handedness Gender Blood group Eye color (i.E. Affected or not affected)
the shape of the Normal distribution of counties Multifactorial Traits?
Bell shape
what is the Multifactorial disease happen in Cardiac Genitourinary Central nervous system Other
Cardiac……… Fallot’s tetralogy
Genitourinary……… Renal dysgenesis
Central nervous system……… Spina bifida
Other……. Cleft lip/palate
recurrence risk for multifactorial Conditions is usually based on what ?
information collected from
observations of a large series of affected
individuals and families
when the -recurrence risk become higher?
More than one family member is affected
➢ The affected individual is of the less
commonly affected sex e.g. Heart disease
➢ The severity of the disease in the individual
is more severe
recurrence in first degree relatives can be calculated: by ?
Square root of incidence of the disease in the population
Heritability meaning and example ?
Estimate of the proportion of the
variability in a trait that is due to
genetic rather than environment
Example: lipid levels vary across the population but less so between family members. Lung Cancer(L) vs breast cancer (H)
mention the Heritability Estimates Very high (>90%) High (>65%) Median) Low (<35%) ) Very low (<10%)
Very high (>90%) Bipolar Autism Body fat percentage Ridge count on fingerprint
Height High (>65%) Asthma BMI Cleft lip Spina bifida
Median)
Blood pressure
Multiple sclerosis
Myocardial infarction (female)
Low (<35%) Myocardial infarction (male)
) Very low (<10%)
Contagious disease
Genetic Epidemiology meaning ?.
To identify the exact genes that contribute to the etiology of the disease condition (or to distinguish genetic and environmental features):
what is the Monozygotic and dizygotic twins ? And concordant And discordant?
Monozygotic (identical) twins single zygote genetically identical
concordant
(monozygotic) both twins share a trait
Dizygotic (fraternal) twins two eggs by different sperm and
are as different from each other genetically
discordant if they do not share the trait
(Dizygotic)
features of autism?
Absence of verbal communication, lack of
social responsiveness,
developmental delay
autism percentage in twins ?
✓ = 80% in monozygotic twins ✓ = 3% in dizygotic twins
how many genes contribute to autism ?
15 susceptibility loci – each
makes a modest additive contribution
What is pylorus?
lower portion of the stomach that connects to the small
intestine
What is pyloric stenosis,?
muscles in pylorus enlarge, narrowing the opening of the pylorus and eventually
preventing food from moving from the stomach to the
intestine
What is the Second most common problem requiring surgery in newborns?
Pyloric Stenosis
pyloric stenosis percentage in twins ? monozygotic?.
25-40% concordance rate in monozygotic twins
compare between Diabetes Mellitus 2 forms from type of people , coplecation percentage ?
Type I – IDDM (insulin dependent DM)
• Juvenile onset
• 0.4% population
• Serious renal, retinal, vascular complications
Type II – NIDDM (non-insulin dependent DM)
• Mature onset
• 5-6% population
• Relatively benign
concordance of Diabetes Mellitus 2 forms?
Type I
✓ 50% monozygotic
✓ 12% dizygotic
Type II
✓ 80% monozygotic
✓ 20% dizygotic
how many genes contribute to diabetes-predisposing?. 2 examples
18 diabetes-predisposing genes
have been reported to date
histocompatibility complex (HLA) region on chromosome 6p21 (IDDM1) and the insulin gene on chromosome 11p15 (IDDM 2) have been conclusively associated with susceptibility to type 1 diabetes
Environmental factors of type II – IDDM ?
low birth weight
obesity
middle aged
Example of genes that point to an increased risk of type 2 diabetes
E .g: Zinc transporter
gene (regulating insulin secretion)
what is the percentage of people death because of Coronary Artery Disease?
50%
from where Results Coronary Artery Disease?
atherosclerosis (lipid deposition in
arteries) – leads to myocardial infarction
Environmental risk factors of Coronary Artery Disease?
poor diet, cigarette
smoking, stress
Coronary Artery Disease percentage in twins ?
Concordance:
➢ 39-48% in monozygotic twins
➢ 15-25% in dizygotic twin
definition of Epistasis?
.type of gene interaction where an allele at a
particular locus alters the phenotypic expression of
another non-allelic gene
✓ i.e. Phenotypic expression of one gene is
influenced by another gene
• The action of one gene is modified by one or several
other non-allelic genes
modification of
the phenotype of one gene by another gene
type of Epistasis?
synergistic enhancing the
effectiveness) or
antagonistic (reducing the activity)
Examples of Epistasis?
Suppressor Genes – encode a genetic
factor that prevents the expression of
alleles at a second locus
dominant
disorders, such as polydactyly (extra
fingers or toes), appear to skip generations
up-regulation of the gamma chain
compensates for loss of β -globin
sickle cell disease or some of the other
haemoglobinopathies e.g. thalassaemias
