Euploid Have the normal chromosome number Polyploid A cell with extra sets of chromosomes Ex triploid 3n Aneuploid Cells missing a single chromosome or having an extra chromosome Alterations in Chromosome Number ID: 1038777
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1. Chromosome Variations
2. Alterations in Chromosome NumberEuploidHave the normal chromosome numberPolyploidA cell with extra sets of chromosomesEx: triploid (3n)AneuploidCells missing a single chromosome or having an extra chromosome
3. Alterations in Chromosome NumberNondisjunction: occurs when eitherHomologs fail to separate during anaphase I of meiosisSister chromatids fail to separate during anaphase IIResult: one gamete has 2 copies of one chromosome and the other has no copy of that chromosome
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6. Alterations in Chromosome NumberIf either of these gametes unites with another during fertilization, the result is aneuploidy (abnormal chromosome number).Trisomy: extra chromosome (more common)Monosomy: missing a chromosome
7. Alterations in Chromosome NumberFrequency of nondisjunction is quite high in humans, but the results are usually so devastating to the zygote that miscarriage occurs very early in the pregnancy.If the individual survives, he or she usually has a set of symptoms (a syndrome) caused by the abnormal dose of each gene product from that chromosome.
8. Down SyndromeNondisjunction of autosomeTrisomy 21Characteristic facial features, short stature, “floppy” appearance, developmental milestones come slowly, heart & kidney defects, hearing & visual loss, suppressed immune system, greater chance of developing leukemia & Alzheimer diseaseMost common autosomal aneuploid among livebornsLikelihood increases with age of the motherAverage life expectancy is now 60 (in 1910 it was 9)Genome editing to shut off one X chromosome
9. Edward’s SyndromeNondisjunction of autosomeTrisomy 18Great physical & intellectual disabilities, almost every organ system affected: heart defects, displaced liver, growth retardation, oddly clenched fists, overlapping fingers, narrow flat skull, low-set ears, small mouth, unusual fingerprints, “rocker-bottom” feetMost do not survive to be born; children with full trisomy 18 generally do not live more than a few months
10. Patau SyndromeNondisjunction of autosomeTrisomy 13Fusion of the developing eyes; heart, kidney, brain, face, & limb abnormalities; cleft lip/palate; small head; extra fingers/toes; extra spleen; atypical liver; rotated intestines; abnormal pancreasA few have survived to adulthood, but most rarely live more than a few monthsDo not progress developmentally beyond the 6-month level
11. Klinefelter SyndromeNondisjunction of sex chromosomes47XXY (extra X chromosome)Male sex organs; but underdeveloped sexually (small testes and prostate gland, sparse pubic & facial hair)Long arms & legs, large hands & feet, may develop breast tissueAbout 1 in 500 malesMost common genetic or chromosomal cause of male infertility
12. Trisomy XNondisjunction of sex chromosomes47XXX (extra X chromosome)Females; healthy and fertile; usually cannot be distinguished from normal female except by karyotypeOnly symptoms are tall stature and menstrual irregularities; tend to be less intelligent than siblingsAbout 1 in every 1000 femalesAll but one of the X chromosomes in inactivated
13. Turner’s SyndromeNondisjunction of sex chromosomesMonosomy X (45XO): one X chromosome & no 2nd sex chromosome (some are missing only part of an X chromosome)Looks normal at birth, except puffy hands & feetWide-set nipples, soft nails that turn up, slight webbing at the back of the neck, short, coarse facial features, low hairline at the back of the head, impaired hearing, ear infectionsAt sexual maturity, sparse body hair, don’t ovulate or menstruate, breasts don’t develop, small uterusThe only viable monosomy in humansAffects 1 in 2500 female births; 99% of XO fetuses are not born; life span is shortened slightlyMore likely to develop osteoporosis, diabetes, colon cancer
14. XXYY SyndromeNondisjunction of sex chromosomeXXYY (extra X chromosome & extra Y chromosome)More severe behavioral problems, tend to develop foot & leg ulcers from poor circulationAttention deficit disorder, obsessive compulsive disorder, autism, & learning disabilities typically develop by adolescenceLow testosterone, delayed development of secondary sexual characteristics, undescended testesinfertileAbout 1 in 17,000 newborn boysUntil recently was diagnosed as Klinefelter’s
15. XYY MalesNondisjunction of sex chromosomes47XYY (extra Y chromosome)Very tall, acne1 in 1000 malescriminally aggressive hypothesis disproven over time; 96% not destined to become criminals