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Genetics

Genetics. Islamic University College of Nursing. Introduction. Our understanding of human genetics improved in the few past years. This was occurred after the discovery of the gene map.

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Genetics

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  1. Genetics Islamic University College of Nursing

  2. Introduction • Our understanding of human genetics improved in the few past years. • This was occurred after the discovery of the gene map. • Human diseases and the different disorders are influenced by both environmental and genetic factors with varying degrees, for example, Downsyndrome is pure genetic disease, Scurvy is pure due to environmental factors. In between combined such as DM, HTN (Multi-factorial).

  3. Human Cell • Normal human cell contains 46 (23 pairs) chromosomes, 22 pair autosomes and the 23rd chromosome is sex pair. • XX for the female and XY for the male. • Approximately 50,000 genes encoded in the human DNA. (Deoxyriboneuclic Acid)

  4. Cell Division 23 46 Mitosis 23 Meiosis I 23 46 23 23 23 Meiosis II 23 23 23 23 23 23 23 23

  5. Spermatogenesis & Oogenesis • Gametogenesis in male and female are principally the same but differ in timing of the various stages. • Spermatogenesis begin in the seminefrous tubules around the puberty & continue out life. • Oogenesis begin in the intrauterine life but is arrested in meiosis I, with completion of the cycle when ovulation occurs and continue up to 50 years old.

  6. Sexual Division of Ova and sperm Normal 23 Ova 46 Polar body Abnormal Not contain cytoplasm Meiosis I Normal 23 23 Sperm 46 Meiosis II 23 Polar body Abnormal Not contain cytoplasm Not contain cytoplasm

  7. Duplication of genetic materials Female Chromosomes Male chromosomes Short arm (P) The Same Centromere Proteins ABCDEF A B C D E F Long arm (q)

  8. Preparation for genetic study 1- Separation of WBCs by centrifugation. 2- Cultivate the lymphocytes by adding phytohemagglutinin. 3- Arrest cell division after about 70 hours by adding colchicines to the culture. 4- Release the chromosomes from the nucleus by adding hypotonic saline. 5- Fix and stain.

  9. Indications for chromosomal studies • Mental retardation. • Multiple congenital abnormalities. • Recurrent abortion. • Infertility. • Ambiguous sex. • Leukemia. • Failure to thrive child. • Some syndromes. (turner).

  10. Definitions: • Gene: describe the hereditary factor that determine the trait or disorder. • Locus: is the position at which the structural gene lies. Individuals have 2 alleles at each locus. • Homozygous: if the 2 alleles at a singlelocus are identical. (Recessive)

  11. Definitions cont… • Heterozygous: if the 2 alleles in a singlelocus are different. (Dominant) • Dominant: if the condition is manifest with single gene, example heterozygous state. • Recessive: if the condition is seen only in the homozygous state. Occurred when the two alleles are abnormal.

  12. Autosomal Recessive • Recessive: the condition is seen only in the homozygous state. (identical) • Occurred when the two alleles are abnormal. • The disorder is more common among consangeous marriage. Siblings have one half of their genes in common, where first cousins have one-eight of their genes in common. • One third of inherited traits are AR.

  13. Criteria of AR disorders • Parents are usually healthy. • Affected individuals are almost the offspring of heterozygot carrier parents. • Percent % to be affected of children if the parents are carriers is 1:4. • If both parents are affected all children will be affected. • Both sexes are affected equally. • It causes mainly enzyme deficiency. • Example: Cystic Fibrosis, Galactosomia, Phenlketonurea, Thalassemia, and others.

  14. Autosomal Dominant (AD) • Dominant means that the disease allele or gene need to be present only in single copy (heterozygot) to result in phenotype. • The affected individuals posses both the abnormal and normal gene. • More than half of the inherited traits are autosomal dominant.

  15. Criteria of Autosomal (AD) disorder • Disease is transmitted from generation to generation and can be tracked to several generations. • Sporadic cases can occur due to new mutations, it occur more frequently in sever cases in which the chance of survival or reproduction of the affected persons are low. • It affect both sexes equally.

  16. Criteria of Autosomal (AD) disorder • The risk of transmission to the offspring is 50% they show variability in severity. • Anticipation: The severity of the disease tended to increase with each generation. • An example: Myotonic dystrophy, the grandfather could have cataract only, the mother had myotonia and muscle weakness and the affected child had congenital myotonic dystrophy with developmental delay.

  17. Example of AD • Achondroplasia. (disease of bone growth cause short structure M. 131, F124, not able to convert cartilage into long bone). • Neurofibromatosis. (NF1)causes skin changes and deformed bones. It usually starts in childhood. Sometimes the symptoms are present at birth. (NF2) causes hearingloss, ringing in the ears, and poor balance. Symptoms often start in the teen years.

  18. Example of AD • Polycystic Kidney disease. (ADPKD) is a multi-systemic and progressive disorder characterized by cyst formation and enlargement in the kidney and other organs (eg, liver, pancreas, spleen). Up to 50% of patients with ADPKD require renal replacement therapy by 60 years of age. • Retinoblastoma.  (is the most common primary ocular malignancy of childhood). • Spherocytosis.  is a familial hemolytic disorder with marked heterogeneity of clinical features, ranging from an asymptomatic condition to fulminant hemolytic anemia

  19. X-linked diseases • Transmitted by heterozygous mother to sons • Daughters - 50% carriers, 50% healthy • Sons - 50% diseased, 50% healthy • Children of diseased father - sons are healthy, all daughters are carriers • Hemophilia A(defect of Factor VIII) • Hemophilia B(defect of Factor IX) • Muscle dystrophy(Duchen disease)

  20. Autosomal disorders Trisomy 21 (Down syndrome) • Most frequent - 1:700 births; parents have normal karyo-type. • Maternal age has a strong influence: <20 y. 1:1550 live births, >45 y. 1:25 live births • Most frequently is abnormality in ovum (ovum is under long-time influence of environment)

  21. HEREDITY The passing of traits from parent to offspring. • ALLELE The different forms of a trait that a gene may have. One form of a gene • GENOTYPEAn organism's genetic makeup. • PHENOTYPE Outward physical appearance and behavior of an organism. • TRAIT Ways of looking, thinking, or being. Traits that are genetic are passed down through the genes from parents to offspring.

  22. Autosomal Dominant

  23. Autosomal Dominant 50% affected Affect both sexs equally

  24. Autosomal Dominant

  25. Autosomal Recessive

  26. Autosomal Recessive

  27. Autosomal Recessive

  28. Sex linked disease

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