MULTIFACTORIAL

Multifactorial inheritance, also called complex or polygenic inheritance. Multifactorial inheritance disorders are caused by a combination of

environmental factors and mutations in multiple genes. For example, different genes that influence breast cancer susceptibility

have been found on chromosomes 6, 11, 13, 14, 15, 17, and 22. Some common chronic diseases are multifactorial disorders.

CHARACTERISTICS OF MULTIFACTORIAL DISEASE The disease can occur in isolation, with affected children born to

unaffected parents. Although familial aggregation is also common (i.e., there may be multiple cases in the same family), there is no clear Mendelian pattern of inheritance.

Environmental influences can increase or decrease the risk of the disease. The disease occurs more frequently in one gender than in the other, but it

is not a sex-limited trait. In addition, first-degree relatives of individuals belonging to the more rarely affected gender have a higher risk of bearing the disease

The concordance rates in monozygotic and dizygotic twins contradict Mendelian proportions. A concordance rate is a measure of the rate at which both twins bear a specific disease

The disease occurs more frequently in a specific ethnic group (i.e., Caucasians, Africans, Asians, Hispanics, etc.).

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EXAMPLES OF MULTIFACTORIAL INHERITANCE INCLUDE

High Blood Pressure -The cause of essential hypertension is multifactorial

Genetic factors are thought to play a prominent role in the development of essential hypertension.

However, the genes for hypertension have not yet been identified Approximately 30% of cases of essential hypertension are

attributable to genetic factors. For example, in the United States, the incidence of high blood

pressure is greater among African Americans than among Caucasians or Asians. Also, in individuals who have one or two parents with hypertension, high blood pressure is twice as common as in the general population.

The vast majority of patients with essential hypertension have in common a particular abnormality of the arteries:

an increased resistance (stiffness or lack of elasticity) in the tiny arteries that are most distant from the heart (peripheral arteries or arterioles)

Others:

Coronary Heart Disease Alzheimer's disease arthritis diabetes cancer Obesity

Multifactorial inheritance also is associated with heritable traits such as fingerprint patterns, height, eye

color, and skin color.

CYTOGENETICS

Cytogenetics is an exciting, dynamic field of study which analyzes the number and structure of human and animal chromosomes.

Changes that affect the number and/or structure of the chromosomes can cause problems with growth, development, and how the body functions.

Chromosomal abnormalities can happen when egg and sperm cells are being made, during early fetal development, or after birth in any cell in the body

Changes to chromosome structure can disrupt genes, causing the proteins made from disrupted genes to be missing or faulty. Depending on size, location, and timing,

CYTOGENETICS

Cytogenetic analyses are commonly performed during pregnancy to determine if a fetus is at risk for common aneuplodies

Aneuplodies- syndromes caused by having extra or missing chromosomes, syndromes caused by structural abnormalities (like unbalanced translocations or inversions), or to determine if extra or missing genetic material is present through cytogenetic microarray testing. 

The same cytogenetic analyses can be performed on a newborn or child with multiple anomalies or developmental delays to look for a potential chromosomal abnormality

Today, the diagnosis and treatment of several leukemias and lymphomas, as well as some solid tumors, depends heavily on cytogenetic analysis of specific chromosomal aberrations which are consistently observed in these particular cancers.

SINGLE GENE DISORDERS

A single gene disorder is the result of a single mutated gene Over 4000 human diseases are caused by single gene defect Single gene disorders can be passed on to subsequent generations in

several ways. Genomic imprinting and uniparental disomy, however, may affect inheritance p

Prevalence of some single gene disorders Disorder prevalence (approximate)

Autosomal dominant - Familial hypercholesterolemia 1 in 500, Polycystic kidney disease 1 in 1250, Neurofibromatosis type I 1 in 2,500, Hereditary spherocytosis 1 in 5,000, Marfan syndrome 1 in 4,000, Huntington's disease 1 in 15,000

Autosomal recessive - Sickle cell anemia 1 in 625 Cystic fibrosis 1 in 2,000, Tay-Sachs disease 1 in 3,000, Phenylketonuria 1 in 12,000, Mucopolysaccharidoses 1 in 25,000, Lysosomal acid lipase deficiency 1 in 40,000, Glycogen storage diseases1 in 50,000 Galactosemia 1 in 57,000

X-linked- Duchenne muscular dystrophy 1 in 7,000, Hemophilia 1 in 10,000 Values are for liveborn infants atterns.

Autosomal dominant

Only one mutated copy of the gene will be necessary for a person to be affected by an autosomal dominant disorder. Each affected person usually has one affected parent

Autosomal recessive

Two copies of the gene must be mutated for a person to be affected by an autosomal recessive disorder.

X-linked dominant X-linked dominant disorders are caused by mutations in genes on the X chromosome

X-linked recessive X-linked recessive conditions are also caused by mutations in genes on the X chromosome. Males are more frequently affected than females, and the chance of passing on the disorder differs between men and women.

Y-linked Y-linked disorders are caused by mutations on the Y chromosome. Because males inherit a Y chromosome from their fathers, every son of an affected father will be affected. Because females only inherit an X chromosome from their fathers, and never a Y chromosome, female offspring of affected fathers are never affected.

Mitochondrial This type of inheritance, also known as maternal inheritance, applies to genes in mitochondrial DNA. Because only egg cells contribute mitochondria to the developing embryo, only mothers can pass on mitochondrial conditions to their children.

MENDELIAN or Mendelian genetics or Mendelism or Monogenetic inheritance)

is a scientific theory of how hereditary characteristics are passed from parent organisms to their offspring

MENDELS LAW

Law of Segregation (The "First Law")

The Law of Segregation states that every individual possesses a pair of alleles (assuming diploidy) for any particular trait and that each parent passes a randomly selected copy (allele) of only one of these to its offspring. The offspring then receives its own pair of alleles for that trait.

Law of Independent Assortment (The "Second Law")

The Law of Independent Assortment, also known as "Inheritance Law", states that separate genes for separate traits are passed independently of one another from parents to offspring

EXAMPLES

Traits previously believed to be Mendelian

Ability to taste phenylthiocarbamide (dominant)

Ability to smell (bitter almond-like) hydrogen cyanide (recessive)

Albinism (recessive) Brachydactyly

(shortness of fingers and toes)

Wet (dominant) or dry (recessive) earwax

immunity to poison ivy (dominant)

Eyecolor Morton's toe Tongue rolling Hair color Widow's peak

(allele) Detached

(dominant) or attached (recessive) earlobes

Hitchhiker's thumb (recessive)

PRESENTED BY:CARDENAS, NORMA CZARINA M.

DMD-2D