Intro to Genetics Flashcards
Examples of unifactorial diseases
Duchenne muscular dystrophy
Haemophillia
Phenylketonuria
Polygenic inheritance
Phenotype is determined by variants of many genes at diff loci, each allele exerting a small additive effect
Traits showing continuous distribution
Determined by interplay of many alleles at diff loci but influenced by environmental factors
Multifactorial
Phenotype results from the interaction of environmental (incl in utero environment) and genetic factors
Heritability
The proportion of variance in a characteristic attributed to genetic factors for a given pop.
Concordant
If both twins have same trait (incl complex disease phenotypes)
Discordant
If only one twin has the disease
Freq. of concordance is compared for mz and dz twins
Concordance rates in multifactorial traits
Degree of concordance in mz twins exceeds that seen in dz twins but is <100% as a result of diff environmental contributions
When are concordance rates the same in mz and dz twins
When the disease is caused directly by environmental factors
What do family and twin studies measure
Heritability
Heritability estimates can vary over times and between populations
What does the liability threshold model explain
Why we see family clustering for polygenetic and multifactorial traits e.g. heart disease and psychiatric disorders
Examples of autosomal dominant and autosomal recessive monogenic
Huntingtion disease
Hereditary haemochromatosis
Huntington disease
Classic single gene disorder
Inherited as autosomal dominant trait and underlying mutation has v. high penetrance - the chance that a carrier of the mutation (genotype) will eventually express the disease phenotype too
Mutation leading to Huntington’s
Expansion to CAG codon –> expressed as glutamine in the proteins AA sequence
Altered protein is toxic and causes progressive degeneration of the basal ganglia
Altered protein in Huntington’s
Altered protein is toxic and causes progressive degeneration of the basal ganglia and cerebral cortex’s resulting in a range of neurological symptoms
Toxic-gain of function phenotype —> degeneration
Transmission of Huntington’s
Pedigree shows vertical transmission
Anticipation
Age of onset decreases w/ successive generations
Seen in several neurological disorders caused by mutations that involve expansions of trinucleotide repeats
Hereditary haemochromatosis
Used by absorption of too much dietary iron –> accumulates in organs such as liver and heart
Patients have accumulated large iron stores that damage essential organs by the time they are symptomatic so patients present w/ a host of life threatening disease manifestations e.g. liver cancer
Treatment of HH
Venesection
Venesction
Removal of blood - done through phlebotomy needle and leg
Causes of HH
Single nucleotide polymorphisms/ point mutation resulting in change in codons for AA 63 or 282
What are recessive genetic diseases usually associated with
Mutations that result in loss of normal protein function
How does the centromere divide the chromosome
Into the short (p) arm and the longer (q) arm
Classification of centromeres
Done according to the position of the centromere and relative lengths of the p and q arms
Metacentric
Sub metacentric
Acrocentric
Metacentric
Centromere located midway
Sub metacentric
Centromeres placed slightly away from centre
Acrocentric
Centromere placed quite near one end of the chromosome
Telomere
End of chromosome
Isoforms
A single gene encodes for two or more isoforms through alternative splicing
Alternative splicing
Transcripts from coding sequences can be cut up and re-joined in many ways
Why can protein and transcript isoforms occur
Alternative initiation and termination sites for gene expression —> far fewer coding-genes than potential transcripts and protein sequences
Why is plasticity in genome important
For tissue spp gene expression
