Genetics

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Genetics

  1. 1. Marietta M. Diaz,MD,FPPS,FCNSP
  2. 2. <ul><li>Genetic Factors </li></ul><ul><li>Differences in constitutional makeup, basically intrinsic in nature </li></ul><ul><li>Interplay of inherited chromosomes determines the potential physical and mental traits </li></ul><ul><li>Abnormalities of genes or chromosomes contained in the genetic structure of the individual may cause congenital defects </li></ul>
  3. 3. <ul><li>Patterns of Transmission of Traits and Diseases </li></ul><ul><li>Homozygous-both members of pair of alleles are identical </li></ul><ul><li>Heterozygous-when both members of pair of alleles are different </li></ul><ul><li>Single gene or monogenic- when a trait is caused by only a pair of genes </li></ul><ul><li>Polygenic or multifactorial-when brought about by several pairs of genes </li></ul>
  4. 4. <ul><li>Genetype-individual’s full set of genes </li></ul><ul><li>Phenotype-individual’s outward expression of these manifested as physical,biochemical or physiological traits </li></ul><ul><li>Propositus-or index case-the individual member who first brings the family to the attention of the investigator </li></ul>
  5. 5. <ul><li>Autosomal Dominant Inheritance- the gene effects its recognizable trait in the heterozygous form </li></ul><ul><li>Most persons manifesting an abnormal dominant trait are heterozygous </li></ul><ul><li>If the individual marries and the mate is normal, the offsprings of such mating, half is abnormal and the other half is normal </li></ul><ul><li>There is no risk for the normal children to have abnormal children provided the mate is normal </li></ul><ul><li>Ie achondroplastic dwarfism, osteogenesis imperfecta,spherocytosis,Neurofibromatosis </li></ul>
  6. 6. <ul><li>Autosomal Recessive Inheritance- abnormal gene effects a recognizable trait in the homozygous form </li></ul><ul><li>A person with abnormal recessive trait appears normal </li></ul><ul><li>If married to a mate with normal genes all offsprings will appear normal </li></ul><ul><li>If a heterozygote for the trait marries another heterozygote each of the offspring will have one chance out of four of being homozygous and having the abnormal trait </li></ul><ul><li>Ie adrenogenital syndrome,deaf mutism,cretinism </li></ul>
  7. 7. <ul><li>Autosomal Intermediate Inheritance </li></ul><ul><li>Presence of a single abnormal gene determines some degree of abnormality </li></ul><ul><li>Described as incompletely recessive </li></ul><ul><li>Ie Thalassemia gene </li></ul><ul><li>Heterozygote for the gene reveals sign and symptoms of thalassemia minor- mild manifestations and life expectancy is long </li></ul><ul><li>Homozygote manifests a severe disease where the patient does not live long </li></ul>
  8. 8. <ul><li>Sex Inheritance </li></ul><ul><li>Males- XY </li></ul><ul><li>Females-XX </li></ul><ul><li>Theoretically the chances of having either a boy or girl are half and half </li></ul><ul><li>106 boys for every 100 girls </li></ul><ul><li>Difference is explained by the greater probability of a Y bearing sperm to fertilize the ovum since it has less DNA and is thus lighter and more motile </li></ul>
  9. 9. <ul><li>Sex Linked Inheritance- transmission of traits through sex chromosomes; X linked has ore clinical significance </li></ul><ul><li>Main characteristic-absence of father to son transmission- X chromosome of the father is transmitted to none of his sons but to each of his daughter </li></ul><ul><li>X-linked dominant trait-affected males transmit the disease to all their daughters but none of their sons; affected females who are heterozygous transmit the condition to half of their children of either sex </li></ul><ul><li>X-linked recessive trait-expressed by all males who carry the gene but the females are only affected if homozygous; trait is never transmitted directly from father to son but is passed on through his daughters to half of their sons </li></ul>
  10. 10. <ul><li>Multifactorial Inheritance-situation in which the disease is the result of the additive effect of one or more abnormal genes and environmental factors </li></ul><ul><li>Variations in the expression of genes </li></ul><ul><li>Skipping of generation- slight abnormality may not be obvious </li></ul><ul><li>Pleitropy- one gene , several effects- single defect may lead to various abnormalities in fully differentiated structures </li></ul><ul><li>Genetic heterogeneity-several genes, one effect- mutations at different loci can independently produce the same trait </li></ul><ul><li>Variable age of onset </li></ul><ul><li>Environmental effects-manifests the disease only if he encounters certain environmental conditions </li></ul>
  11. 11. <ul><li>Numerical- somatic cells contain an abnormal number of normal chromosomes </li></ul><ul><li>Aneuploidy-chromosome number is not an exact multiple of the haploid set </li></ul><ul><li>-addition or subtraction of one or more whole chromosomes leading to either trisomy or monosomy </li></ul><ul><li>Polyploidy-complete extra set of chromosomes, increasing chromosome number to 69 </li></ul><ul><li>Structural-result from chromosome breakage or rearrangement- translocation, ring chromosome, isochromosome or inversion </li></ul>
  12. 12. <ul><li>Trisomy 21- Down’s Syndrome </li></ul><ul><li>Hypotonia </li></ul><ul><li>Poor moro reflex </li></ul><ul><li>Hyperflexibility of joints </li></ul><ul><li>Flat facial profile </li></ul><ul><li>Upslanting palpebral fissure, low set ears </li></ul><ul><li>simian crease </li></ul>
  13. 13. <ul><li>Trisomy 18-Edward’s Syndrome </li></ul><ul><li>Failure to thrive </li></ul><ul><li>Micrognathia </li></ul><ul><li>Low set ears </li></ul><ul><li>Short palpebral fissures </li></ul><ul><li>Narrow palatal arch </li></ul><ul><li>Rocker bottom feet </li></ul><ul><li>Transverse palmar crease </li></ul><ul><li>Mental retardation </li></ul>
  14. 14. <ul><li>Trisomy 13-Patau Syndrome </li></ul><ul><li>Moderate microcephaly </li></ul><ul><li>Cleft lip and palate </li></ul><ul><li>Malformed ears </li></ul><ul><li>Scalp defects </li></ul><ul><li>Polydactyly </li></ul><ul><li>Rocker bottom feet </li></ul><ul><li>Cryptorchidism </li></ul>
  15. 15. <ul><li>Cri-du-chat Syndrome-5 p-syndrome </li></ul><ul><li>Low birth weight </li></ul><ul><li>Failure to thrive </li></ul><ul><li>Hypotonia </li></ul><ul><li>Hypertelorism </li></ul><ul><li>Cat cry </li></ul><ul><li>Epicanthal fold </li></ul><ul><li>Downward slant of the palpebral fissure </li></ul><ul><li>Strabismus </li></ul><ul><li>Low set ears mental retardation </li></ul>
  16. 16. <ul><li>Wolf Hirschorn Syndrome-4 p Syndrome </li></ul><ul><li>Growth retardation </li></ul><ul><li>Hypotonia </li></ul><ul><li>Hypertelorism,prominecleft lip/palate </li></ul><ul><li>Downturned”fishlike mouth” </li></ul><ul><li>Short upper lip and philtrum </li></ul><ul><li>Micrognathia </li></ul>
  17. 17. <ul><li>9 p Syndrome </li></ul><ul><li>Craniosynostosis </li></ul><ul><li>Upslanting palpebral fissures </li></ul><ul><li>Short nose </li></ul><ul><li>Depressed nasal bridge </li></ul><ul><li>Short neck short distal phalanges </li></ul>
  18. 18. <ul><li>Turner Syndrome-45,X </li></ul><ul><li>Short stature </li></ul><ul><li>Neck web </li></ul><ul><li>Cubitus valgus </li></ul><ul><li>Lack of secondary sexual characteristics </li></ul><ul><li>Primary amenorrhea </li></ul><ul><li>infertility </li></ul>
  19. 19. <ul><li>Klinefelter Syndrome- XXYSyndrome </li></ul><ul><li>Long limbs </li></ul><ul><li>Underdeveloped genitalia </li></ul><ul><li>Infertility </li></ul><ul><li>Sparse body hair </li></ul><ul><li>Mental retardation </li></ul>
  20. 20. <ul><li>Triple Female Syndrome-47,XXX Female </li></ul><ul><li>Delayed motor development </li></ul><ul><li>Delayed speech </li></ul><ul><li>Mild intellectual deficit </li></ul><ul><li>Normal gonadal function </li></ul><ul><li>Fertile </li></ul>
  21. 21. <ul><li>History </li></ul><ul><li>Physical examination </li></ul><ul><li>Laboratory examination </li></ul><ul><li>Computerized data base-POSSUM-pictures of syndromes and undiagnosed malformations </li></ul><ul><li>Genetic counselling </li></ul>
  22. 22. <ul><li>Controlling the external environment </li></ul><ul><li>Regulating ingested food </li></ul><ul><li>Modifying external environment </li></ul><ul><li>Removing disease tissues or introducing normal donor tissue </li></ul><ul><li>Genetic engineering </li></ul><ul><li>Preventing conception or birth of affected individuals by genetic counselling </li></ul>

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