Heredity and Genetic Diseases

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Heredity and Genetic Diseases
2012-07-24 16:43:19
Heredity Genetic Diseases

Heredity and Genetic Diseases
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  1. Deoxyribonucleic acid (DNA)
    Blueprint for directing cellular activities especially protein synthesis
  2. Each cell contains
    • 46 human chromosomes (a chromosome contains thousands of genes)
    •   [1] 44 chromosomes are called autosomes 
    •   [2] 2 chromosomes are sex (X or Y) chromosomes
    • 2 meters of DNA
    • 3 billion base pairs
    • 25,000
    • genes code for the synthesis of a particular protein, RNA, or DNA
  3. Base Pairs
    • [1] Adenine (A)
    • [2] Thymine (T)
    • [3] Cytosine (C)
    • [4] Guanine (G)
  4. DNA undergoes self replication
    • a) By a process known as meiosis or reductional division where the number of chromosomes per cell is cut in half
    • [1] Interphase is the period of cell growth where genetic material is duplicated
  5. DNA codes for its partner ribonucleic
    acid (RNA)
    Interaction of DNA and RNA program hereditary and  etabolic activities
  6. Karotype
    A photomicrograph for visualizing extracted chromosomes from a cell nucleus for determining potential chromosomal abnormalities
  7. Allele
    • One of two or more version of a gene
    • (1) An allele occupies a specific site on a chromosome
    • (2) Each parent has two sites or copies of the gene
    • (3) One copy of the gene is transferred from each parent to their offspring
    • (4) Offspring genotype can follow one of three patterns:
  8. Offspring genotype can follow one of three patterns:
    • (a) Pair of alleles the same- [1] Homozygous for a trait 
    • (b) Pair of alleles differ [1] Heterozygous for a trait
    • (c) Dominant allele [1] Some alleles always produce their
    • trait when inherited
    •  (d) Recessive allele [1] These alleles only manifest their
    • effect when a person is homozygous for a trait [2] Recessive alleles are significant in many hereditary diseases
  9. Punnett Square
    A chart that shows or predicts all possible gene combinations in a cross of parents whose genes are known
  10. Co-dominant alleles
    • [1] Both traits are expressed when both alleles are inherited
    • [2] Both alleles are equally strong
    • [3] Both alleles are visible in the phenotype
    •  [4] ABO blood system is an example of co-dominant alleles
  11. Reduced penetrance
    • [1] A dominant allele is not fully expressed
    • {a} Possible factors having a role in modifying gene expression include
    • {1} Other genes
    • {2} Environmental conditions
    • {3} Gender
    • {b} Syndactyly, webbing in fingers and
    • toes, is an example of reduced penetrance
  12. Transmission of hereditary diseases or disorders
    • A genetically determined illness transmitted from
    • parent to child
  13. Transmission of hereditary diseases or disorders - Possible causes
    • Metabolic breakdown caused by a lack of direction from either a
    • [1] Missing gene
    • [2] Compromised gene
    • [3] Chromosomal segment
    • [4] A specific protein that is either missing or defective
  14. Three main types genetically determined diseases or
    disorders are recognized
    • Autosomal dominant hereditary diseases
    • Autosomal recessive inherited diseases or disorders
    •  Sex (X chromosome)-linked inheritance
  15. Autosomal dominant hereditary diseases
    • [1] Usually transmitted from parent who is heterozygous for the trait, while the other parent is normal
    • [2] Each child has a 50% chance of being afflicted with the disorder
    • [3] Disease appears in every generation
    • [4] Males and females are equally affected
  16. Huntington’s chorea
    • Autosomal dominant hereditary diseases
    • Develops in adulthood and ends in dementia
    • {2} Chorea is a degenerative nervous disorder characterized by spasmodic movements of the body and limbs
    • {3} An inherited disease controlled by a
    • single pair of genes
    • {4} Caused by a dominant mutant gene on
    • an autosomal allele
  17. Polydactyly
    {1} Extra fingers or toes

    {2} Evident at birth

    {3} Not a major disorder
  18. Achondroplasia
    • {1}Cartilage development in fetus abnormal and is gradually replaced by bone (ossification)
    • {2} Leads to a form of dwarfism
    • {3} Trunk (torso) of body normal size
    • {4} Long bones of arms and legs affected
    • {5} Head is large, forehead prominent
    • {6} Normal intellectual, sexual, and muscular development
  19. Marfan syndrome
    • {1} A disorder of gene which codes for the connective tissue protein fibrillin
    • {2} Defects found in the skeletal system and cardiovascular system
    • {3} Diagnosis
    • {a} Blood (DNA) tests for lack of fibrillin
    • {b} Echocardiogram to detect aortic dilation and floppy heart valves
    • {4} Disease onset is by age 20 years
    • {5} Death due to heart failure or ruptured aortic aneurysm
  20. Familial hypercholesterolemia
    • {1} Caused by gene encoding the low-density lipoprotein (LDL) receptor
    • {2} Diagnosis
    • <1> Blood screening for increased LDL cholesterol
    • {3} Leads to atherosclerosis and increased incidence of coronary heart disease
    • {4} Disease caused by incomplete dominant gene activity
  21. i.e. Autosomal dominant hereditary diseases
    • Huntington’s chorea
    • Polydactyly
    • Achondroplasia
    • Marfan syndrome
    • Familial hypercholesterolemia
  22. Autosomal recessive inherited diseases or disorders
    • [1] Both parents are carriers of disease with no overt disease
    •  [2] Disease is found in homozygous individual
  23. Hemochromatosis
    • {1} A disorder that results in too much iron being absorbed from the gastrointestinal tract
    • {2} Most common genetic disorder in the USA
  24. Phenylketonuria (PKU)
    • {1} Due to an inborn metabolic error
    • {2} Infant lacks enzyme to convert phenylalanine to tyrosine
    • {3} High phenylalanine levels are toxic
    • and interfere with normal brain development resulting in severe mental retardation
    • {4} Diagnosed by blood test (heelstick)
    • to determine PKU in newborn
    •  {5} Treatment is special diet to prevent
    • phenylalanine build-up and mental retardation
  25. Galactosemia
    • {1} Due to an inborn metabolic error
    • {2} Infants lack enzyme to convert galactose to glucose
    • {3} Blood galactose accumulation interferes with brain, liver, and eye development
    • {4} If untreated- mental retardation and liver is enlarged and becomes cirrhotic
    • {5} Treatment aimed to eliminate dietary lactose
  26. Sickle
    cell anemia
    • {1}High incidence in African-American population
    • {2} Caused by an abnormal hemoglobin called hemoglobin S that distorts the shape of red blood cells especially under low oxygen conditions
    • {3} Homozygous person has full blown disease
    • {4} Heterozygous person has sickle cell trait which can impart resistance to malaria
  27. Tay-Sachs Disease
    • {1} Occurs in people of Eastern Europeanand Ashkenazi Jewish descent
    • {2} Caused by insufficient activity ofbeta-hexosaminidase A that is necessary to catalyze the degradation of GM2ganglioside
    • {3} Build-up of GM2 ganglioside levels in tissues damages brain nerve cells producing progressive mental retardation and physical regression
    • {4} Symptoms appear by 6 months of age
    • {5} No treatment is available
    • {6} Children usually die between 2 and 4years of age by recurring infections
    •  {7} Prevention may require genetic counseling and prenatal testing
  28. Albinism
    • {1} Occurrence is rare in general population, but there is a high incidence in Hopi Native Americans
    • {2} Due to decreased melanin levels
    • {3} Characterized by decreased or lackof color in the skin, hair, and eyes
    • {4} Associated with increased risk forskin cancers
    • {5} Exhibit visual problems such as nearsightedness and abnormally high sensitivity to light
  29. i.e  Disease is found in homozygous individual
    • Hemochromatosis
    • Phenylketonuria (PKU)
    • Galactosemia
    • Sickle cell anemia
    • Tay-Sachs Disease
    • Albinism
  30. Sex (X chromosome)-linked inheritance
    • [1] X-linked diseases usually occur in males since males have only one X chromosome
    • [2] A single recessive gene on the X chromosome will cause disease
    • [3] Y-linked diseases (?)
    • [4] An inherited trait determined by a gene on the Y chromosome
    • [5] There a few genetic diseases related to specific genes on the Y chromosome
    • [6] Y-linked transmission or male sex determination due to sex-determining region Y (SRY) gene found on the Y chromosome
    • [7] SRY gene specifics maleness and male features by initiating cascade of hormones (testosterone) in utero that make a person male
  31. Cystic fibrosis
    • {1} An inherited disease that causes thick, sticky mucus to build-up in the lungs and digestive tract
    •  {2} One of the most chronic lung diseases in children and young adults and may result in early death
  32. Red-green color blindness
    • {1} Men more affected by this disorder than women
    • {2} Due to a defect in specialized retinal cells called cones
    •  {a} Cones are stimulated by wavelengths of primary colors- red, green, and blue
  33. Hemophilia
    Refers to a group of bleeding disorders taking a long a time for blood to clot
  34. Hemophilia A
    <1> Factor VIII deficiency

    <a> Highest percentage of cases

    • <b> Disorder primarily affects
    • males
  35. Hemophilia B
    • <1> Factor IX deficiency
    • <a> Second highest percentage of cases
    • <b> Disorder primarily affects
    • males
  36. Hemophilia
    • <1> Factor XI deficiency
    • <a> Autosomal recessive disease
    • <b> Few percentage of cases
    • <c> Found in persons of Jewish ancestry
    • <d> Affects males and females equally
  37. Treatments
    for hemophilia
    • {a} Intravenous blood or plasma transfusions to replace missing clotting factors (VIII, IX, or XI)
    • {b} Infusion of genetically engineeredrecombinant clotting factors (VIII, IX, or XI)
    • {c} The synthetic hormone desmopressinused to primarily treat mild hemophilia A (desmopressin causes release of factor VIII)
  38. Fragile
    X syndrome
    • 1} Identified by thin, thread-like strands on long arm of X chromosome
    • {2} The thin, thread-like strands are weak and subject to breakage
    • {3} Mothers are carriers, sons at greatest risk of being affected, and daughters tend to be carriers, but may be slightly affected
    • {4} Most common cause of mental retardation
    • {5} No cure, treatments used to improve attention
    • deficits and hyperactivity
  39. Familial
    • Diseases appearing in families, but means of inheritance is not understood
    • Not one gene, but possibly several genes involved- multifactorial
  40. Familial diseases include
    • <1> Epilepsy
    • <2> Diabetes
    • <3> Cardiovascular disease
    • <4> Allergies/asthma
    • <5> Familial polyposis
  41. Familial diseases  Causes
    may include
    <1> Environmental conditions

    • <2> Shared behaviors of family
    • members
  42. i.e Sex
    (X chromosome)-linked inheritance
    • Cystic fibrosis
    • Red-green color blindness
    • Hemophilia
    • Fragile X syndrome
    • Familial diseases
  43. Abnormal chromosome diseases