types of inheritance
TRANSCRIPT
By Kimmer Collison-RisMSN, FNP-C, WOCN, MS CAM
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This presentation discuss the various types of inheritance from: Dominant-recessive inheritance through Polygene inheritance
What do they do? They trace the transmission of
genetically encoded traits, conditions or diseases to offspring.
Several modes of inheritance: -Single Gene (Mendelian)
-Multifactorial
-Mitochondrial
Punnett Squares Used to figure out for
single gene inheritance the possible gene combinations that can result from mating 2 parents with of known genotypes.
Traits w/dominant alleles include: Freckles
Dimples
Widow’s peaks
Definition: A type of genetic disease caused by mutation in DNA sequence of 1 gene that alters the protein.
Types of Single Gene Inheritance:Autosomal: it’s the gene responsible for the phenotype that is located on 1 of 22 pairs of autosomes (non-sex determining chromosomes)
X-linked: the gene that encodes for the trait which is located on an X chromosome
Dominant: conditions that occur in heterozygotes , persons with only 1 copy of a mutant allele
Recessive: conditions only occur in persons who have >2 copies of a mutant allele (homozygous).
Definition: Autosomal dominant disorders are generally transmitted
from parent to child through one or more generations or can result from a new mutation.
The disease will typically shows a “Mendelian pattern” of inheritance-Males & females are equally affected
Examples:
-Albinism
-acondroplasia (short-limbed dwarfism)
-Huntington's disease
-polycystic kidney disease
-deafness
Affected children have parents that possess both a mutant & functioning copy of the allele (affected)
Autosomal recessive diseases:
-Cystic fibrosis
-Sickle cell anemia
-Tay-Sachs
Definition: These are inherited traits that are determined on the genes of the sex chromosomes (X and Y)
Y : gene that determines maleness
-is physically smaller
-carries only 78 genes-codes for clotting factors
-codes for cone pigments-certain alleles expressed
X : is physically larger
-carries over 2,500 genes
-contains many proteins that code for brain function
X-linked traits gen. passed from mom to sonFemales must have (2) X linked recessive alleles to exhibit a specific disorder
X-linked Recessive Disorders:• Duchenne muscular dystrophy• hemophilia A• X-linked severe combined immune disorder (SCID)• some forms of congenital deafness
Sex-linked genetic diseases :-Duchenne muscular dystrophy-Hemophilia-red/green colorblindness
-rarely seen in females
Definition: a gene that is located on an X chromosome, that causes no transmission from father to son, but occurs from father to daughter (as all daughters will be affected since father has (1) X chromosome to give.
Children of an affected mom have a 50% chance of inheriting the X chromosome with the mutant allele
X-linked dominant disorders clinically occur when (1)copy of the mutant allele is present.
X-Linked Traits and MutationsX-Linked Recessive X-Linked Dominant
Mom: CARRIER,Dad: noncarrier
Each daughter:25% noncarrier25% carrier
Each son:25% noncarrier25% affected
Mom: noncarrierdad: affected
Each daughter:100% carrier
Each son:100% noncarrier
Mom: affecteddad: noncarrier
Each daughter or son:50% affected50% nonaffected
Mom: noncarrier
dad: affected
Each daughter:100% affected
Each son:100% nonaffected
http://www.beltina.org/health-dictionary/inheritance-patterns-autosomal-traits-x-linked-mutation.html
http://cw.tufts.edu
Definition: where the heterozygote has a phenotype intermediate between those of homozygous dominant and homozygous recessive persons.
-Typically uncommon in humans.
Examples: sickle-cell anemia,Hemoglobin SS disease (Hb SS) or Sickle cell disease
Note: persons heterozygous for the sickling gene (Ss) have sickle cell trait, causing them to make normal and abnormal sickling hemoglobin.
Autosomal Traits & Mutations
Autosomal Recessive Autosomal DominantBoth Parents are Carriers
1 parent carrier,1 parent not carrier
Each child:- 25% condition- 25% noncarrier- 50% carrier
Each child:- 50% noncarrier- 50% carrier
Both parents affected
1 parent affected, 1 parent unaffected
Each child:- 25% unaffected- 25% more severely affected- than parents- 50% affected
Each child:- 50% unaffected- 50% affected
Polygene Inheritance
Definition: where many phenotypes rely upon several alternate gene pairs that can occur simultaneously and at different locations on a gene.
Causes:
-continuous phenotypic variation
or
-quantitative phenotypic variations
Note: this is the reason there is such extremes in characteristics
Examples: skin color, metabolic rate, height variations, & intelligence (skin color alone relies upon 3 separate, inherited genes : A,a, B,b, C,c)
Polygenetic Inheritance…
http://wikispaces.psu.edu
Definition: where although we inherit just (2) alleles for every gene, genes can exhibit more than (2) allele forms which causes multifactorial inheritance.
Example: blood types that determine ABO compatibility(expressed IA, IB, and i)IA and IB are codominant and “i” is recessive to them
Definition: where many diseases have multifactorial inheritance patterns
-these conditions result from many genetic &environmental factors.
-are not genetically determined, but result from mutations that predispose persons to a specific disease
-additional genetic & environmental factors can influence the disease developingGenetic heterogeneity-many genetic alterations will influence a person acquiring a specific disease
Example: CAD risk factors include hyperlipidemia, diabetes, & high blood pressure
-those risk factors have genetic & environmental pieces
Note: this is why multifactorial inheritance is more complex than Mendelian inheritance and WHY its difficult to trace via pedigree
Common Multifactorial Conditions:
• Alzheimers disease• heart disease
• insulin-dependent diabetes mellitus• intelligence• some cancers• neural tube defects•schizophrenia
Example: A family pedigree from a BRCA1 gene mutation. Here a father can be a carrier & pass the gene along to a child. Because not all people who acquire the gene develop the disease, its difficult to trace the transmission.http://www.uvm.edu/~cgep/Education/Inheritance2.html
Definition: many diseases are transmitted by mitochondrial inheritance affecting organs with high-energy use (ie. heart, kidneys, skeletal muscle, & liver.
-This kind of inheritance occurs as a result of transmission from a mom to a child, so all children will inherit this but not all will necessarily be affected. Note: Mitochondria are organelles in the cell cytoplasm.
-they make multiple copies of a circular chromosome.
-their main function is to convert molecules into usable energy.
This is the least common pattern of inheritance
http://www.beltina.org/health-dictionary/inheritance-patterns-autosomal-traits-x-linked-mutation.html
https://www.biologis.com/pgs/benefit/carrier-status
http://cw.tufts.edu
http://geneticalliance.org.uk
http://www.uvm.edu/~cgep/Education/Inheritance2.html
http://mdmedicine.wordpress.com/2011/04/07/types-of-inheritance/
http://wikispaces.psu.edu