Genetics Test 2
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Not everyone with a disorder has each and every known manifestation of that disorder.
End result of Bayesian analysis is a ______
Several physicians may use the same ovservations to arrive at differing "degrees of belief"; patients want to know if they have a disorder, not our belief system
Screening tests shoud have high __________
Confirmatory tests should have high ________
A test often dow not prove or rule out the presence of a disorder (it may change the probability)
Informed consent issues
Basis of Baye's Theorem:
There is no certainty
Begin with a model that limits all possibly hypotheses to a constrained subset in the model: typically two or more ________ hypotheses; each with its own prior probability
Probability obtained from the pedigree
Appears normal at age 34, given either genotype (in relation to the problem)
How well the test detects affected people. Formula?
How well the text excludes unaffected people. Formula?
How often the test misclassifies affected people as "not affected"?
How often the test misclassifies affected people as "not affected". Formula?
If the test result is positive, what's the probability the patient has the disease?
If the test result is normal, what's the probability the patient does not have the disease?
What values help answer the above questions?
Two important questions sensitivity and specificity don't answer.
____ and _____ are very dependent on the disease prevalence, in addition
PPV and NPV
What type of test is used to "rule out" a diagnosis and hsould have a high sensitivity?
What type of test is used to "rule in" a disease and should have a high specificity?
Explain to a family that neither a normal or an abnormal test result has 100% predictability. This should have been explained to the family prior to initiating the consent. When specifically?
While obtaining informed consent
What fraction of offspring from two carrier parents will be unaffected in autosomal recessive traits?
Of the unaffected offspring, 2/3 of the offspring will be heterozygotes.
- 3/4 will be unaffected
What is the study of the frequency of alleles and traits in a population; and the study of the factors that affect gene or genotype frequencies.
What can provide the carrier frequency in a population, making possible genetic counseling about recurrence risks in a kindred?
How many mutations are present for an AR disorder?
How many lethal equivalents?
______ is a fallacy. We can eliminate all deleterious genes from a population only by eliminating completely that population.
Eugenic policies curtail individual freedom, claiming to promote the interest of a future society.
Promotes propagation of more "desirable people" types
Seeks to decrease propagation of more "undesirable people" types
Improvements in medical management do lead to increased biological fitness of _________
Hardy-Weinburg Law assumes
- Mating is random and in a large population
- No selection for or against any genotype
- No migration into or out of the population
- No new mutations
(These are never completely met.)
Relates the genotype frequencies at a Mendelian locus to the phenotype frequencies in that population.
- p2 + 2pq + a2
- p + q = 1
The values of p and q are the same in males and females since we share all X chromosomes. This is in relation to?
X-linked Recessive Traits
But affected males are more frequent than affected females.
Non-random mating (2 examples):
Leads to increased ______
Exposes _______ traits to selection
- 1) Assortative Mating, 2) Consanguinity and incest
- increased homozygosity
- recessive traits
Selection for a similar mate based upon ethnicity, religion, stature, deafness, etc.
Relationship between cloose blood relatives.
Incidence in US?
Risks in offspring:
- 1st = 50; brother- sister, parent-child
- 2nd= 5-10; uncle-niece
- 3rd= 3-5; first cousins
A union between individuals so closely related that the union is illegal. It is between?
1st Degree (brother-sister, parent-child)
10-15% of mothers of sporadic cases are
What mutations are more frequent among children born of older fathers?
New single gene dominant mutations (apert sydrome, achondroplasa)
Acrocephalocyndactyly, craniosyntosis, mid-face hypoplasia, prominence of orbits
An equilibrium may exist between new mutations and selection for or against a mutant allele, tending to maintain allele frequencies constant.
What disorders are not often recognized because all cases are sporadic.
Autosomal dominant, complete genetic lethal disorders
Migration of people changes the allel frequency in a region (ie. hispanics into USA)
Small "isolated" population effects
Allele frequency can occur in small populations by chance.
- Random fluctuation
- Leads to extinction, fixation, and the founder effect on some alleles.
A case of genetic drift in which a small founder population with limited genetic variation derives from a larger population, resulting in a large change in allele frequencies.
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