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HUMAN GENETICS

HUMAN GENETICS. Genetic disorders- common cause of diseases, prolonged handicap and death in human. 1% newborns have monogenic diseases like CF, SCD etc. 0.5% have chr . disorders like Down Synd. 1-3% have multifactorial disorders like CHD,

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HUMAN GENETICS

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  1. HUMAN GENETICS Genetic disorders- common cause of diseases, prolonged handicap and death in human. • 1% newborns have monogenic diseases like CF, SCD etc. • 0.5% have chr. disorders like Down Synd. • 1-3% have multifactorial disorders like CHD, spina bifida. • 40% deaths due to genetic disorders & birth defects.

  2. HUMAN CELLS • Human genome has 25000 genes (basic unit). • Human cell somatic / germ line (sperm/ovum) • Each somatic cell has 23 pair of chromosomes (diploid No.). . 22 pairs of autosomes . 1 pair of sex chr. (xx/xy). • Germ line cell has 23 chromosome (haploid No.) . 22 autosome . 1 sex chromosome(X/Y).

  3. CHROMOSOME • Each chromosome has 2 chromatids . • Upper small arm “p” and lower large “q”. • Attached in center “ centromere ”. • Each p / q arm has 350-850 bands. • Each band has specific serial No. • E.g. William Synd. due to deletion at 7q11.23 means disease gene at band 11.23 of “q” arm of chromosome 7.

  4. Genotype/phenotype • Genotype: Genetic constitution of an individual. • Phenotype: Observed structural , biochemical and physiological features of an individual.

  5. MUTATION Spontaneous change in genetic material 1-Gain function mutation; over expression / inappropriate expression of a gene product . Mostly produce AD disorder e. g. achondroplasia. 2-Loss of function mutation; observed in AR disorders, 50% enzyme activity in hetrozygote- allow normal function e.g. SCD

  6. FAMILY HISTORY Most important screening tool to identify pt.’s risk for development of variety of diseases. . Multifactorialcondition: Diabetes M . cleft lip and palat, neural tube defects. . Single gene disorders:likeSCD, Cystic fibrosis osteogenesisImperfecta etc. . Parents, siblings and offsprings share 1/2 genetic material & first cousins 1/8 .

  7. PEDEGREE NOTATION • It provides a graphic presentation of a family’s structure & medical Hx. • Arrow represents Information provider(proband). • 1st degree relative (parents, siblings and children) share ½ genetic information. • 1st cousins share 1/8 genetic material.

  8. ABNORMALITIES OF CHROMOSOME NO. Euploidy: If a cell has No. of chr. exact multiple of 23. • n =23, haploid cell (ovum/sperm) • 2n= 46, diploid cell (somatic cell) • 3n= 69, triploid cell (2 sperm+1 ovum, non- disjunction , viable only in mosaic case). . paternal origin—hydatidiform mole. . maternal origin—spontaneously abort.

  9. ANEUPLOIDY Abnormal cell having no multiple of 23 chr. . It is most common chr. abnormality. . 3-4% pregnancies, only mosaic viable. . Mostly due to non-disjunction. . Monosomy e.g. Turner synd.(45,X0) . Trisomy, most common e.g.21,18,13. . Klinefelter synd.(47,XXY)

  10. MITOSIS • Somatic cells divide themselves to grow an organ. • 4 stages- . prophase . metaphase . anaphase . telophase • Duplication of DNA-divide to 2 daughter cells.

  11. MEIOSIS • In reproductive/germ line cells (sperm / ovum) • In 2 rounds (meiosis 1 & 2) it completes. • After duplication of DNA ,one germ line cell (diploid No.=46 chromosome)divide into 4 ( haploid No.23 chr.) gametes(ovum/sperm). • Zygote formation (x + y) maintain diploid No.

  12. ABNORMAL CHR. STRUCTURE TRANSLOCATION: Transfer of genetic material from one to other chromosome. • Incidence-1:500 in live borns. • Inherited from parent /de novo. • usually phenotypically normal. • high chances of miscarriage/ chromosomically abnormal offspring.

  13. INVERTION A chromosome breaks at 2 points , broken piece is inverted & joined into same chromosome. • Incidence-1:100 live borns. • Carriers are phenotypically normal. • High chances of miscarriage/chromosomically abnormal offspring .

  14. DELETION / DUPLICATION Deletion: A piece of chromosome missing. • Usually associated with mental retardation & malformations. • “5p-” (deletion at “p” arm of chromosome No.5) Duplication: Presence of extra gen. material from same chr.

  15. INSERTION A piece of chr. broken at 2 points is incorporated Into a break in an other part of chromosome. • 3 break points required. • May occur between 2 or within samechr. • Carrier have high risk of having offspring with deletion or duplication of inserted segment. • Incidence is rare.

  16. ISOCHROMOSOME Two copies of same chr. arm joined through a single centromere forming mirror image of one another.

  17. RING CHROMOSOME Both ends of a chr. are deleted and re-joined to form a ring. • Carrier are normal/nearly normal /may have mental retardation & multiple congenital anomalies.

  18. SEX CHR. ABNORMALITIES • Incidence- 1:400 in males & 1:650 in females. • Most common chr. abnormalities in live borns. • Numerical / structural. • Present in all cell / mosaic. • Carrier have few / no physical & developmental problems.

  19. TURNER SYNDROME • Incidence- 1:5000 female live borns . • Partial / complete absence of 2nd X chr. • 50%pt. have(45,X0) and 50% are mosaic. • 95-99% of 45,X0 conceptions miscarried. • Phenotype-variable especially in mosaic pt.

  20. Turner Syndrome

  21. EDWARD SYNDROME (Trisomy 18)

  22. POLYPLOIDY Euploid cells having >diploid No.(2n=46) chr. . Also called heteroploid cells. . Usually conceptions not viable. . Mosaic karyotypically normal line viable.

  23. NOONAN SYNDROM • AD disorder- 60% cause is new mutation. • In both male/ female. • Features almost same as in Turner Synd.

  24. NOONA SYNDROME

  25. KLINEFELTER SYNDROME • 80% are male with an extra X chr. (47,XXY). • Commonest cause of hypogonadism & infertility. • 50% cause is paternal non-disjunction. • Secondary sex characters- delayed. • 50% develop gynaecomastia. • Remained unidentified until puberty. • No intellect , show deficit in language.

  26. MOSAICISM Person with 2 > cell lines from single zygote. • 2% in early pregnancy- chr. abnormal mosaic. • Except trisomies 21,18,13, usually non viable. • Mosaicism may be in some tissues only. • Germ line /reproductive cells mosaicism increase risk of recurrence in affected children.

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