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