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![Important definitions in Genetics
Aneuploidy = Addition or loss of one (rarely two) chromosome.
Trisomy = 3 copies of a chromosome, (2n+1)
Tetrasomy = 4 copies of a chromosome, (2n+2)etc
Monosomy= 1 member of a chromosome pair missing, (2n-1) that is
only single copy of a chromosome is present.
Euploidy = Normal condition, where the genotype consists of complete
two sets of chromosomes (23+23 or 2n).
Genotype = Genetic make up of cell.
Karyotype = Number and appearance of chromosome in a nucleus.
Non disjunction = Incorrect separation of chromosomes or sister
chromatids during meiosis.
Phenotype = Characteristics of an Organism
Polyploidy = Entire extra set of chromosomes present, [can be
triploidy(3n= 69 chromosomes),tetraploidy(4n=92 chromosomes) etc.]](https://image.slidesharecdn.com/mahtab-170117094859/75/dr-Mahtab-5-2048.jpg)
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dr Mahtab
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- 2. Contents Introduction Classificationof Genetic Disorder Autosomal Anomalies Structural Chromosomal Anomalies Sex Chromosome Anomalies Structural Chromosomal Anomalies
- 3. Definition & prevalenceChromosomal Anomalies = Missing, extra, or irregular portion of chromosomal DNA. Most foetus with some chromosomal abnormality do not survive. Affects approximately 1 out of 200 of new-borns. Karyotype = Full set of chromosomes from an individual. (Chromosomal Anomalies can be detected via Karyotype Testing.) Abnormalities depends on type of chromosome affected due to non-disjunction chromosomes.
- 4. basics HUMAN CHROMOSOME46 XX/XY
- 5. Important definitions inGenetics Aneuploidy = Addition or loss of one (rarely two) chromosome. Trisomy = 3 copies of a chromosome, (2n+1) Tetrasomy = 4 copies of a chromosome, (2n+2)etc Monosomy= 1 member of a chromosome pair missing, (2n-1) that is only single copy of a chromosome is present. Euploidy = Normal condition, where the genotype consists of complete two sets of chromosomes (23+23 or 2n). Genotype = Genetic make up of cell. Karyotype = Number and appearance of chromosome in a nucleus. Non disjunction = Incorrect separation of chromosomes or sister chromatids during meiosis. Phenotype = Characteristics of an Organism Polyploidy = Entire extra set of chromosomes present, [can be triploidy(3n= 69 chromosomes),tetraploidy(4n=92 chromosomes) etc.]
- 6. GENOTYPE Genetic makeup of a particular individual Eg- 46XX/46XY/45XO PHENOTYPE Physical expression of that particular genotype Eg-Male/Female basics
- 7. Chromosome anomaliesusually occur when there is an error in cell division following meiosis or mitosis. There are many types of chromosome anomalies. They can be organized into two basic groups, numerical and structural anomalies.
- 8. Numerical This iscalled aneuploidy (an abnormal number of chromosomes), and occurs when an individual is missing either a chromosome from a pair (monosomy) or has more than two chromosomes of a pair (trisomy, tetrasomy, etc.). Eg of numerical chromosomal anomalies are Down syndrome, edward syndrome, patau syndrome
- 9. Classification of Genetic Disorder Singlegene disorders Chromosoma l Disorder Autosomal Numeric Structural Sex Chromosome Numeric Structural Multifactorial Disorder Acquired Somatic Genetic Disease
- 15. Single chromosome disorder Can happen in a chromosome itself, the other is not required. Deletion (Genetic material missing) may be terminal or interstitial.termina l more common Duplication (Genetic material present twice) Inversion (Genetic material is “flipped”)
- 16. Two Chromosome DisordersNeed 2 chromosomes to occur these processes. Insertion (Genetic material is added from another chromosome) Translocation (Material is swapped(exchanged) with another chromosome)
- 17. Common deletion 4P-WOLF HIRSCHHORN SYNDROME. THE MAIN FEATURE ARE A TYPICAL GREEK HELMET FACIES 9P- MAIN FEATURE ARE CRANIFACIAL DYSMORPHOLOGY WITH TRIGOCEPHALY ,SLANTED PALPEBRAL FEATURE ,EXOPTHALMUS,SECONDARY TO SUPRA ORBITAL HYPOPLASIA JACOBSON SYNDROME DELETION FROM CHROMOSOME 11
- 18. Deletion inthe 4p arm Distinctive facial features - prominent forehead, wideset eyes, and broad beaked nose, collectively described as "Greek warrior helmet" features Brain and muscles - profound mental retardation, small head, seizures (50% of individuals), low muscle tone, poor muscle development Bones - very short stature, facial deformities, malformations of hands and feet, chest, and spine Heart defects Urinary and genitals - malformations or underdevelopment of organs
- 20. Jacobsen Syndrome lossof genetic material fromchromosome 11. Most affected individuals have delayed development of motor skills and speech, cognitive impairment and learning difficulties, distinctive facial features, and a bleeding disorder
- 21. Cri-Du-Chat Syndrome (chromosome 5pdeletion syndrome) Name is based on the infant’s cry. (high-pitched and sounds like a cat.) Incidence =1 in 216,000 birth Normal 46 chromosomes but, missing a piece of chromosome number 5. Cat like cry of affected children ie meowing kitten These babies are usually small at birth , have respiratory problem Microcephaly, micrognathia, low set ear Wide set eye and downward slant of the eyes
- 22. Cri-Du-Chat Syndrome (chromosome 5pdeletion syndrome) Cry is high pitched and similar to that of a meowing kitten. Moon-shaped face Malformed larynx Difficulty swallowing and sucking (Feeding Problem). Low birth weight and poor growth. Severe cognitive, speech, and motor delays, mental retardation Behavioural problems such as hyperactivity, aggression, and repetitive movements. Excessive drooling(ptyalism)
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- 24. Known disordersin humans include Wolf-Hirschhorn syndrome, which is caused by partial deletion of the short arm of chromosome 4; and Jacobsen syndrome, also called the terminal 11q deletion disorder.
- 25. Sex Chromosome Anomalies(Numeric) Monosomy Turner’s syndrome (45,X0) Trisomies Klinefelter's syndrome (47,XXY) Jacob’s syndrome (47,XYY) Triple x syndrome (47,XXX)
- 26. Sex Chromosome Anomalies (Structural) Y-Linked Disease VeryRare X-Linked Disease X-Linked Dominant X-Linked Recessive
- 27. Fragile X syndrome Also known as Martin-Bell syndrome; Marker X syndrome. Some consider this syndrome as X-linked dorminant, some consider this as X-linked recessive which some claims this to be not under X-linked dorminant or recessive. Genetic condition involving changes in the long arm of the X chromosome. Characterized by mental retardation. Fragile area on X chromosome tends to repeat bits of the genetic code .it is repetition of CGG gene in long arm of x chromosome. (*More repeats, the more likely there is to be a problem i.e intellilectual disabilities.) Male and female can both be affected. Male have only one X chromosome, single fragile X more likely to affect them more severely.
- 28. Fragile x syndrome Mainfeature in male Mental retardation Autistic behaviour Large testicles (macro-orchidism) Large size face and ear Tendency to avoid eye contact Hyperactive behaviour Large forehead and/or ears with a prominent jaw Hyper extensible finger joint Female having varying degree of intellilectual and learning disabilities
- 29. Fragile X syndromeKaryotype
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- 34. Turner Syndrome Sexchromosomal monosomy(45, XO) 99% of foetuses with Turner syndrome result in spontaneous termination during the first trimester. Incidence = 1 in 5000 live birth
- 35. TURNER SYNDROME (Physical impairments) Short stature Skeletal disorders (osteoporosis which may lead to scoliosis) Webbed neck(due to cystic hygroma) Broad shoulders Broad chest (shield chest), widely spaced nipples No/Poor breast development Narrow hips (High waist-to-hip ratio: hips are not much bigger than waist) Lymphedema of hands and feet Shortened metacarpal IV Cubitus valgus Normal intelligence
- 36. TURNER SYNDROME (Clinical Features) Underdeveloped ovaries(streak gonads, hence this syndrome also called ovarian dysgenesis) Sterile, lack expected secondary sex characteristics Amenorrhoea(No menstruation) Cardiovascular problems in 40 % (Bicuspid aortic valve,Coarctation of the aorta,aortic stenosis) Renal anomalies 60% eg Horse shoe kidney Thyroid problems (hypothyroidism specifically Hashimoto's thyroiditis).
- 39. Klinefelter’s syndrome XXYMales Disorder occurring due to nondisjunction of the X chromosome during Meiosis. Extra X chromosome is nondisjunction during meiosis II of the germ cell in the female. Occur when sister chromatids on the X sex chromosome fail to separate. XX ovum produced and when fertilized with a Y- sperm it yields XXY offspring. Also occurs X and Y sex chromosomes fail to separate, producing a sperm with an X and Y chromosome & fertilize with normal X ovum produces XXY offspring. Incidence = 1 in 580 live male births.
- 40. Klinefelter’s syndrome variations 48, XXYY (male) syndrome Incidence = 1 in 18,000–40,000 births 48,XXXY Incidence = Extremely rare
- 41. Klinefelter’s syndrome Clinical featuresChildhood Weaker muscles and reduced strength. Puberty (features become more prominent due to hypogonadism (less amount of testosterone produced): so generally dianosed at puberty. Phenoypically male Rounded body type Broader hips Little body hair is present Gynecomastia (increased breast tissue) Microorchidism (i.e. small testicles) Azospermia leading to infertility Micropenis Tall stature IQ is normal ,those having higher x chromosome counts show impaired cognition each addition x chromosome reduces iq 10-15 points.
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- 45. INTRODUCTION Generally in sexualreproduction, the organism bear diploid number of chromosomes i.e they contain two set of homologous chromosomes. Out of these two sets of chromosomes one inherited from the mother and other from father. In some cases zygote is diploid , but both chromosomes are exceptionally inherited from only one parent(from only mother or father) is called uniparental disomy (UPD). Fig:1 showing the normal zygote and uniparental disomic zygote
- 46. When the bothchromosomes inherited from only mother called maternal UPD. Mat UPD has been observed on 2,7,14,15, X chromosome. It is meiotic in origin. When the both chromosomes inherited from only father called paternal UPD. Pat UPD has been observed on 6,11,15,20, X and XY chromosome. It is mitotic in origin. The most common mechanisms leading to UPD include chromosomal non disjunction in the first or second meiotic division, but sometime errors in mitosis and somatic recombination may also lead to UPD. UPD may lead to disorders because maternal and paternal genomes are not equivalent on all chromosome. UPD syndromes • Prader-Willi syndrome (PWS) • Angelman syndromes (AS) • Beckwith-Wiedemann syndrome(BWS)
- 49. Prader-willi syndrome Growthretardation,mental retardation,hypotonia,obesity,hyperphagia Growth asymmetry Hypo/hyperglycemia Feeding deficulties
- 50. ANGELMAN SYNDROME (AS) Angelmansyndrome (AS) is a neuro genetic disorder. It is caused by the loss of normal maternal chromosome 15q11-13. Symptoms severe mental retardation • development delay • Severe speech impairment , , absent speech • Problems with movement and balance (ataxia).,epilepsy • Behavior uniqueness any combination frequent laughter/ smiling apparent happy demeanor, easily excitable personality, sleep disturbance. • Unusually fair skin with light coloured hair. Angelman syndrome affects an estimated 1 in 12,000 to 20,000 peoples.
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