Basic Genetics Concepts
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Basic Genetics Concepts
Basic principles of inheritance, pedigree analysis, risk analysis, and population genetics
individuals homozygous for the disease allele
most affected individuals have unaffected parents
manifests in males and females equally
autosomal recessive and dominant
progeny of two affected individuals are affected
unaffected parents with affected offspring may be consanguinous
heterozygotes and homogygotes (often worse) are both affected
affected progeny have at least one affected parent
can typically assume affected parents are heterozygotes
homozygous females and hemizygous males typically affected
Carrier females typically unaffected
100 % of sons from affected mothers are affected, 50% of sons of carrier mothers are affected, and 0 of progeny from affected fathers are affected
Anyone with affected allele will be affected
Females heterozygous and homozygous; males hemizygous
Severity of diseases in males>females, male lethality
Incidence of affected females can be > than affected males due to male lethality
50% of children of carrier mothers will be affected, 100% of daughters of affected fathers will be affected, 0% of sons of affected fathers will be affected
Only males with affected Y are affected
All sons of affected male will be affected
Mostly relate to fertility and/or sexual development, father-son transmission rare
Coeffecient of relationship
degree of relationship
Coefficient of inbreeding
F=r x 1/2
Law of addition
Law of multiplication
+ 2pq + q
Genotype for p
Genotype for 2pq
Genotype for q
In the Hardy-Weinberg equation, q is equal to
the frequency of affected alleles
In the Hardy-Weinberg equation, p is equal to
the frequency of unaffected alleles
In order for a disease to be considered vertically transmitted....
every affected individual must have an affected parent
F=Father, M=Mother, CR= Carrier Risk, TR= Transmission Risk
Equation for incorporation population genetics into risk
disease characterized by an absence of clotting factors
disease characterized by loss of pigment in the skin hair, and eyes and a tyrosinase (melanin synthesis) defect
disease characterized by a lack of dystrophin protein and is very well characterized (around 2 mil. base pairs)
Duchenne Muscular Dystrophy
Duchenne Muscular Dystrophy
disease characterized by abnormal HGB, causing RBCs to stickle and have low O
carrying capacity; leads to easy RBC clotting and breakage
disease characterized by skin spots and optic glioma
disease characterized by fibrillin mutations and tall stature & long phalanges
Neurodevelopmental disorder, males usually die if they have it
disease that affects the flow of chloride ions across the plasma membrane; affectssweat glands and glands that produce mucus & digestive enzymes
A form of dwarfism
disease characterized by extra copy of chromosome 21; considered a chromosomal disorder
*can present like AR if reduced penetrance
disease characterized by extra digits; notorious for skipping generations
Examples of multifactorial disorders
Alzheimer's and Hirschprung (disease characterized by GI problems/constipation)
disease characterized by motor abnormalities and personality/cognition changes
Heterozygotes resistant to malaria
disease characterized by cherry spots on the retina; has a founder effect in Ashkenazi Jews
An easy way to find the probability of
being a carrier in a Bayesian table
Subtract the probability from 1
The conditional, "not a carrier" side of a Bayesian table is almost always ____.
The main difference between doing AR & AD H-W problems and doing XLR ones is
it is only necessary to find p & q, not 2pq, because there is no such thing as a male carrrier.
For example, for a carrier frequency of 1/20 in a population of 2000 (1k M, 1k F):
**carrier frequency=factoring in the female population
formula for the chance of having unaffected grandsons in XLR Bayesian analysis
1/2 + 1/2 (1/2)
# of grandsons
Formula to determine the likelihood of an affected child in Bayesian
(PC)(TR)(Penetrance (if available))
If an AR Bayesian problem has an unaffected son, you must...
make two separate tables
The 2/3 method cannot be used if....
there is more than one affected son.
The risk is then 1.
Reduction in chromosome number occurs during
Segregation of alleles in the absence of recombination occurs during
Segregation of alleles if they are subject to recombination occurs during
Independent assortment of paternal and maternal chromosomes occurs during
Occurs in the germ line cells to produce gametes
Occurs in somatic cells
Not directly related to Mendelian inheritance, but is important for genetic diseases like cancer
Makes exact genetic copies of cells
Cell products have 1/2 of original cell chromosome content and contain a mixture of paternal and maternal chromosomes, at least some of which have undergone recombination
Fundamental to Mendelian inheritance and understanding chromosome disorders.
Disorders that follow simple Mendelian predictions of inheritance
Disorders that have an environmental component
Disorders that involve the nuclear genome directly
All disorders BUT mitochondrial ones
Diseases that involve a genome other than the nuclear genome
Disorders that involve the simultaneous mutation of more than one gene in an affected individual
polygenic and/or multifactorial disorders
Diseases that involve one or more genes in an individual with a normal set of chromosomes
All BUT chromosomal disorders
Diseases that involve changes in chromosome number or large portions of chromosomes
4 Nucleotides of DNA
A, G, T, C.
Pairings of DNA nucleotides
AT & GC
After DNA replication, humans have ___ chromosomes.
Has 3 Billion base pairs per haploid genome and 20-25K unique genes per haploid genome
Has around 16,000 base pairs and 37 genes total
Comprised of several nearly identical circular chromosomes of double-stranded DNA
Comprised of several distinct linear double-stranded DNA molecules, one molecule of DNA/chromosome
The largely random inactivation and transcriptional silencing of single X chromosomes into a Barr body in females, which happens early in female development.
Can increase the occurrence, severity, and penetrance of heterozygous females for an affected allele of an x-linked recessive disorder.
The individual of focus during pedigree analysis.
Empiric risk is calculated using
Consanguinuity, selection, genetic drift, new mutations, assortative mating, and new mutations...
Can cause deviation from HW