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48 Cards in this Set
- Front
- Back
What is the likely diagnosis? How can you tell? |
FAP - lots of polyps |
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What is a polygenic disorder? |
A condition not controlled by a single gene, but contributed to by multiple genes |
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Give some examples of congenital malformations arising from multifactorial inheritance? |
- cleft lip/palate - congenital hip dislocation - congenital heart defects - spina bifida - pyloric stenosis - clubfoot |
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Give some examples of acquired diseases with polygenic inheritance |
Asthma Autism Diabetes Epilepsy Crohn's disease Ischaemic heart disease Hypertension Multiple sclerosis Parkinsons Psoriasis Osteoarthritis Schizophrenia |
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What is the relative impact of mutations in monogenic diseases vs those ofpolygenic diseases? |
A mutation in a monogenic disease will have a much greater impact on the function of the gene product, so is more severe. However they are rarer. Polygenic diseases are more moderate but more common |
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What does it mean to say the genes in a polygenic disease have a cumulative effect? |
No gene is dominant or recessive to any other, instead the mutations add up to increase the severity of the disease |
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How can the liability of a polygenic disease be modelled? |
Using a normal distribution |
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True or false - genes can generate a continuous trait when they act together |
True |
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Give some examples of continuously distributed human characteristics |
Height Weight Head circumference Intelligence Waist size |
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If polygenic diseases are continuous in their risk, how do we determine whether someone has a disease or not? |
The disease will only manifest itself once a threshold of susceptibility has been passed - the threshold model of susceptibility |
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How does the liability of siblings of affected people compare to that of the general population? |
Sibling risk is higher compared to normal risk |
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What is recurrence risk? |
The risk that a disease will reoccur elsewhere in a pedigree, given that at least one member of the pedigree exhibits the disease |
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What is homozygocity mapping? |
A method of mapping recessive traits in consanguineous families |
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What is heritability? |
The proportion of the total phenotypic variance of a condition which is caused by additive genetic variance Essentially, how much of a disease is caused by genetics and how much by the environment |
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How heritable are the following conditions? Schizophrenia Asthma CL+P Spina bifida Coronary artery disease |
Schizophrenia - 85%Asthma - 80%CL+P - 76%Spina bifida - 60%Coronary artery disease - 65% |
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What can researchers do to assess the heritability of a disease? |
Twin pair studies |
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What does monozygotic mean? What proportion of twins are monozygotic? |
Twins developed from a single fertilised egg, which then split into 2. 1/3 of twins are born this way |
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What does dizygotic mean? What proportion of twins are born this way? |
The twins were formed from two separate fertilised eggs. 2/3rds of twins are born this way |
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What is a concordance rate? What does it mean for heritability? |
The proportion of twins that both have the same disease, eg cystic fibrosis has a 100% concordance rate in monozygotic twins and a 25% in DZ twins. Type 1 diabetes has a 36% concordance rate in MZ |
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What are the potential pitfalls of twin pair studies? |
MZ twins are the same sex whereas DZ twins aren't necessarily
MZ twins are often treated differently to DZ twins, which could influence behaviours and environmental traits
MZ twins share more intrauterine tissue than DZ, so intrauterine environmental causes may be confused for genetic causes |
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What technique is used for identifying genes that cause multifactorial disorders? |
Genome-Wide Association studies |
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What technique is used to identify genes that cause single gene diseases? |
Whole Genome Sequencing |
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Describe some features of autism |
- a neurodevelopmental disorder - disproportionately affects males - disorder of social interaction - may cause poor communication, intellectual disability, repetitive behaviours - debate over whether autism is a disability or just neurodivergence |
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What is the Hardy Weinburg Distribution? Why is it useful? |
It allows us to predict the incidence of affected and carrier individuals in a population |
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Give some factors that can disturb the ideal Hardy-Weinburg equilibrium |
Non-random mating New mutations Selection Small population size Gene flow and migration |
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What is reproductive fitness? |
The ability of a person to survive and reproduce |
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Why might some conditions reduce reproductive fitness even if they have no direct effect on physical health? |
Often, conditions causing undesirable cosmetic features can reduce one's ability to reproduce |
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What is positive selection? Give an example |
When a mutation in a gene is selected for because it conveys an advantageous trait In sickle cell anaemia, being homozygous for the normal allele (HbAHbA) makes you susceptible to malaria. Being homozygous for the sickle cell allele (HbSHbS) gives you sickle cell. Being heterozygous protects you from both |
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Give 3 examples of positively selected diseases and the diseases they protect against? |
Sickle cell protects against malaria Thalassemia protects against malaria Cystic fibrosis protects against typhoid fever |
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What is genetic drift? (think Ross the barman) |
The change in frequency of a genetic variant over time. Ross is a carrier for a rare genetic mutation, which he passes on frequently as he has increased reproductive opportunity His kids are more likely to be carriers Their kids are more likely to suffer |
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The effects of genetic drift is most exaggerated in large or small populations? |
Small |
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What is genetic flow? |
The migration of alleles from one population to another |
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What is the founder effect? |
The reduced genetic diversity in populations founded by a small number of people |
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What is the modern definition of a polymorphism? |
The co-existence of 2 or more alleles at a genetic locus at the population level |
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Give an example of a common balanced polymorphism |
Some people have the D allele for ACE production, making them more able to gain strength
Some people have the I allele, making giving them more endurance |
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What diseases are commonly found in Mediterranean populations? |
Sickle cell and thalassaemia |
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What disease is commonly found in Maori populations? |
Crohn's disease |
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What disease is commonly found in Finland? |
Familial CJD |
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What diseases are commonly found in Amish populations? |
Maple syrup urine disease MCAD |
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What diseases are commonly found in the Ashkenazi Jew population? |
Tay Sachs Riley-Day Familial breast cancer |
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What are the potential problems associated with genetic testing? |
It may be barred by certain religions Non-English speaking women may not be able to communicate properly with doctors, or be overridden by male partners There may be a misinformed belief that any genetic abnormality is the fault of the parents |
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What are the choices available for women who can't have children? |
Adopt Use an egg or sperm donor Use a surrogate |
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What common tests are performed to test during pregnancy? |
Amniocentesis CVS NIPT |
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What test can be done prior to pregnancy? Why is this advantageous? |
Pre-implantation genetic testing, is good because it avoids the need to terminate a pregnancy |
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Describe CVS |
Chorionic villus sampling, taking a sample of the placenta at 10-12 weeks. Confers a 2% risk of miscarriage |
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Describe amniocentesis? |
Taking samples of amniotic fluid containing Fetal cells, at around 16-18 weeks, carries 0.5-1% miscarriage risk |
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Describe how PGD works |
Pre-implantation Genetic Diagnosis Create a series of embryos by IVF, remove 1 cell from each embryo at the 8 cell stage and test this cell for mutations If there is a mutation free embryo, implant it |
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True or false - you can choose to implant an affected embryo even if there is a healthy one available |
False |
