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consanguinous mating:
- aka: inbreeding
- reproduction between closely related people
- the closer the relative is related to the proband/consultand the more likely it is that they share a common genotype
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primary relative
- immediate relative
- 1 position away on the descent line
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secondary relative
2 positions away on the descent line
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tertiary relative
3 positions away on the descent line
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multifactorial inheritance
- aka: polygenic inheritance
- multiple genes determine a single trait
- the more genes involved the more continuous the variation
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intelligence
- multifactorial
- nature vs. nurture
- monozygous tins show substantial evidence for a genetic basis to intelligence
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heritability
- a correlation between phenotype and genotype
- H=1: populations phenotypic variance due entirely to genotype
- H-0: variance due to environment
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observational studies
predict the futrue based on the past using emperical risk figures
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3 ways to measure multifactorial inheritance
- heritability
- correlation between specific DNA marker sequence
- emperical risk figures
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approaches used with multifactorial inheritace
- pedigrees
- twin studies
- heritability
- DNA associative studies
- emperical risk figures
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family patterns of multifactorial inheritance
- 1. family risk is higher than the general population
- 2. family risk drops the further away you are
- 3. recurrent risk higher if multiple family members are affected
- 4. risk often related to severity
- 5. may exibit threshold expression
- 6. prior history useful to determine approx recurrant risk
- 7. primary relatives risk = square root of the populations risk
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multifactorial inheritance:
- very difficult to explain at molecular level
- some degree of continuous variability, heredity, and familial aggregation (autosomal dom. with reduced penetrance)
- envrionment plays a role in expression
- everything is somehow genetic
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population genetics attemps:
to address the complex issue of how genes are distributed in populations
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populations genetics answers what questions
- what is the genotype of a typical person
- how common are carriers
- what determines pop frequency of disease
- what factors effect frequency of genes in pop
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populations have 3 genetic characteristics
- 1. gene poop
- 2. allelic frequencies
- 3. genotypic and phenotypic frequencies
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gene pool:
sum total of all alleles in the reproductive gametes from members of a mendillian population
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hardy-weinburg equilibrium
- the state of balance between allelic frequencies
- 1. no mutations
- 2. no migration
- 3. no assortative mating
- 4. no selecion
- 5. no genetic drift
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equation for HW equilibrium
1= p2+ 2pq+ q2
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ABO blood system
- O is recessive
- A and B are co-dominant
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major histocompadability complex
- produces human leukocyte antigen
- genes are inherited as a group-haplotypes
- certain HLA types are associted with disease
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B27 HLA haplotype associated with:
high risk of ankylosing spondylitis
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antibody
a protein coded for by a gene
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how to infectious agents gain acess to the body
by binding to specific cell surface molecules coded for by genes
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cancer
- when cells lose control of their cell cycle
- some run in families meaning cancer is a disease of genes
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proto-oncogenes
- promote cell division
- form oncogenes- promote uncontrolled cell division
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tumore suppressor gene
inhibit cell division
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knudson hypothesis
- carcinogenesis requires multiple tumore suppresor gene mutations
- two-hit model
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sporadic cancer
- most cancers
- both TSGs must be mutated for cancer
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familial cancer
inherit one bad TSG, other one mutates
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cancer immortality
released from restraints on # of mitotic cells
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most breast cancers and colon cancers are: (sporadic or familial?)
sporadic
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when is your risk of developing breast cancer increased?
- if you have BRCA1 and 2
- have 60-80% risk of developing cancer
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mitochonrial genetics
- reproduction is unpredictable
- only recieve mitochondria from moms oocyte- mitochondrial genes are maternal
- distrobution of variant ones in body is unpredictable
- mitochondrial disorder inheritance is very hard to predict
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Nutritional genetics
- there is diversity in the ability of a person to process or metabolize nutrients
- nutrients can alter gene expression
- nutrients may alter compounds that affect other metabolic pathways
- variations in adsoprtion ability
- nutrients are a form of nruture
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genetic counseling
a collaborative effort between health profesionals
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goal of cenetic counseling
to expose patients to methods of prevention, aboidance, and amelioration of these disorders
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what is the chance of having another affected child??
autosomal recessive
25%
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what is the chance of having another affected child??
autosomal dominant
50%
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what is the chance of having another affected child??
rare, sex linked recessive
25%
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what is the chance of having another affected child??
trisomies of autosomes
slight increase over general populations
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what is the chance of having another affected child??
multifactorial inheritance
- usually < 10%
- look at emperical risk figures
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information to gather before genetic counseling
- what is the exact diagnosis
- know facts/family history (pedigree)
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refer cases requireing genetic counseling
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red flags of genetics
- Family: history
- G: groups of congenital abnormalities
- E: extreme/exceptional presentation
- N: neurodevelopmental delay/degeneration
- E: extreme/exceptional pathology
- S: surprising lab values
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reasons for prenatal diagnosis
- 1. late maternal age (35+)
- 2. prior child with chromosomal defect
- 3. history of miscarriage
- 4. known defect in parent
- 5. family history of genetic disease in high risk ethnic group
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new therapies for genetic defects
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high-tech genetic therapies include
- DNA analysis and repair
- disruption of defective genes
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hemochromatosis inheritance
autosomal recessive
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huntingtons disease inheritance
autosomal dominant
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osteogenesis imperfecta inheritance
autosomal dominant
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neurofibromatosis type 1 inheritance
autosomal dominant
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achondroplasia inheritance
autosomal dominant
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marfan's syndrome inheritance
autosomal dominant
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polycystic kidney disease inheritance
autosomal dominant
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Phenylketonuria inheritance
autosomal recessive
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albinism inheritance
autosomal recessive
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tay-sachs disease inheritance
autosomal recessive
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cystic fibrosis inheritance
autosomal recessive
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familial hypercholesterolemia inheritance
autosomal co-dominant inheritance (Aa- semi affected)
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sickle cell anemia
autosomal co-dominant inheritance (Aa= semi affected)
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klinefelters syndrome
male with female-like qualities
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turner's syndrome
female with male-like qualities
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hemophilia A inheritance
x-linked recessive
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common colorblindness inheritance
x-linked recessive
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duchenne-type MD inheritance
x-linked recessive
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fragile-x syndrome inheritance
x-linked recessive
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male pattern baldness inheritance
x-linked recessive
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adolescent idiopathic scoliosis
- multifactorial linheritance
- scoliosis- multiple forms, AIS most common
- common: females have larger curves than males
- autosomal dominant with reduced penetrance
- penetrance: 60%
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spondys
- multifactorial inheritance
- condition of pars interarticularis, common source of LBP
- common
- autosomal dominant with reduced penetrance
- penetrance: 40%
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congenital dislocation fo the hip
- multifactorial inheritance
- displacement of the femoral head outside the acetabulum prior to or slightly after birth
- common in caucasians
- autosomal dominant with reduced penetrance
- shown to run in families, more in females
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ankylosing spondylitis
- multifactorial inheritance
- autoimmune spondyloarthopathy condition
- chronic, painful, progressive inflammatory arthritis affecting primary spine and SI joint leading to fusion
- associated with HLA-B27
- familial aggregation and genetic predisposition
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Neural tube defects
- multifactorial inheritance
- embryonic failure to fully close the developing tube
- listed as autosomal dominant
- 1 in 1,000 people
- recurrent risk is 4% in siblings
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pyloric stenosis
- multifactorial inheritance
- substantial narrowing of the stomach pylorus
- significant hypertrophy and hyperplasia of the pylorus
- not uncommon: 1 in 400
- autosomal dominant with reduced penetrance
- threshold trait- will occur when multiple factors cause an anomalous variation in the pylorus
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cleft lip/palate
- multifactorial inheritance
- developmental failure of fusion of maxillary process and frontal process
- not uncommon: 1 in 700
- autosomal dominant with variable expressivity/severity
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recurrent risk of cleft palate
- previous child: 2%
- parent had it: 6%
- previous child and parent had it: 15%
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club foot
- multifactorial inheritance
- congenital anomalies characterized by a foot that is twisted in and down
- colloquial term for a collection of skeletal deformities that include talipes equinovarus
- autosomal dominant with reduced penetrance
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diabetes mellitus
- multifactorial inheritance
- common and on the rise: 1 in 3
- type 1= autoimmune, type 2= insulin resistance
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recurrent risk of type 2 DM
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hypertension
- when of unknown origin it is deemed essential which is about 95% of cases
- polygenic because there are a number of genes that contribute to it
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eugenics
- application of selective principles upon mankind by mankind
- positive: encouraging those with desirable traits to reproduce (Hitler)
- negative: discouraging those with undesirable traits from reproducing
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