Part 3

• Chromosomal abnormalities


  Genetic anomalies in which an individual may have an atypical number of chromosomes (karyotype) or a structural abnormality in one or more chromosomes
• Chromosome anomalies


  Usually occur when there is an error in cell division following meiosis or mitosis
• Chromosomal abnormalities


  Genetic anomalies in which an individual may have an atypical number of chromosomes (karyotype) or a structural abnormality in one or more chromosomes
• Changes in chromosome number

  • Polyploidy
  • Aneuploidy
• Chromosome anomalies


  Usually occur when there is an error in cell division following meiosis or mitosis
• Polyploidy


  A change in whole chromosome set, having more than one set of homologous chromosomes
• Changes in chromosome number

  • Polyploidy
  • Aneuploidy
• Polyploidy


  A change in whole chromosome set, having more than one set of homologous chromosomes
• Polyploid plants are often larger and have larger components than their diploid relatives
• Polyploid plants are often larger and have larger components than their diploid relatives
• Aneuploidy


  Changes in parts of chromosome sets, having extra copy or missing copy of a chromosome
• Aneuploidy


  Changes in parts of chromosome sets, having extra copy or missing copy of a chromosome
• Nondisjunction


  Failure of segregation of homologous chromosomes or chromatids to opposite poles during cell division
• Nondisjunction


  Failure of segregation of homologous chromosomes or chromatids to opposite poles during cell division
• Monosomy


  Missing one copy of a chromosome
• Monosomy


  Missing one copy of a chromosome
• Turner Syndrome


  Genotype: XO, short in stature, lack prominent female secondary sexual characteristics, ovaries do not develop normally, unsuitable for reproduction
• Trisomy


  Having extra copy of a chromosome (three copies)
• Down Syndrome (Trisomy 21)


  Frequency of ~0.15% of all live births, mental retardation, broad flat face, eyes with epicanthic fold, short stature, short hands with crease across the middle, females may be fertile, males are typically infertile, incidence related to maternal age
• Klinefelter Syndrome


  Genotype: XXY, relatively high-pitched voices, asexual to feminine body contours, little facial and body hair, usually have learning difficulties, testes and prostate gland are small, produce relatively small amounts of testosterone
• Triple X Syndrome (Trisomy X)

  Genotype: XXX, usually taller than average with unusually long legs and slender torsos, usually in the low range of normal intelligence, tend to be emotionally immature, normal development of sexual characteristics and are fertile
• XYY Syndrome


  Genotype: XYY, usually tall (>6 feet), during adolescence often slender, have severe facial acne, and are poorly coordinated, produce high levels of testosterone, usually fertile and lead ordinary lives as adults
• Female Genotype Syndromes


  • XX (normal)
  • XO (Turner Syndrome)
  • XXX (Triple X Syndrome)
• Male Genotype Syndromes


  • XY (normal)
  • XXY (Klinefelter Syndrome)
  • XYY (XYY Syndrome)
• Turner Syndrome


  Genotype: XO, short in stature, lack prominent female secondary sexual characteristics, ovaries do not develop normally, unsuitable for reproduction
• Chromosome structure changes


  DNA breakage is the major cause, repair systems in the cell correct the double-stranded breaks by joining broken ends back together
• Trisomy


  Having extra copy of a chromosome (three copies)
• Balanced rearrangement


  Chromosomal abnormality where the overall chromosome number is normal but the structure is altered
• Down Syndrome (Trisomy 21)


  Frequency of ~0.15% of all live births, mental retardation, broad flat face, eyes with epicanthic fold, short stature, short hands with crease across the middle, females may be fertile, males are typically infertile, incidence related to maternal age
• Klinefelter Syndrome


  Genotype: XXY, relatively high-pitched voices, asexual to feminine body contours, little facial and body hair, usually have learning difficulties, testes and prostate gland are small, produce relatively small amounts of testosterone
• XYY Syndrome


  • Genotype: XYY
  • Produce high levels of testosterone
  • Usually fertile and lead ordinary lives as adults
• Chromosomal Abnormalities


  • Changes in chromosome number
  • Changes in chromosome structure
• Aneuploidy


  Trisomy (2n+1)
• Balanced Rearrangements


  • Change chromosomal gene order but do not remove or duplicate any DNA
  • Same amount of genetic material after the rearrangement
• Triple X Syndrome (Trisomy X)

  Genotype: XXX, usually taller than average with unusually long legs and slender torsos, usually in the low range of normal intelligence, tend to be emotionally immature, normal development of sexual characteristics and are fertile
• Unbalanced Rearrangements


  • Change in the amount of genetic material after the rearrangement
  • Change the gene dosage of a chromosome segment
• XYY Syndrome


  Genotype: XYY, usually tall (>6 feet), during adolescence often slender, have severe facial acne, and are poorly coordinated, produce high levels of testosterone, usually fertile and lead ordinary lives as adults
• Female Genotype Syndromes


  • XX (normal)
  • XO (Turner Syndrome)
  • XXX (Triple X Syndrome)
• Fragile X syndrome


  • Chromosome duplication
  • Fragile site at Xq27.3
  • Normal: 29 "repeats" at this end of X chromosome
  • With Fragile X: over 700 repeats due to duplication
  • Affects 1:1500 males, 1:2500 females
  • Most common form of mental retardation
  • Facial abnormalities
  • Macroorchidism (unusually large testes)
  • Connective tissue abnormalities
• Cri-du-chat syndrome


  • Chromosome deletion
  • Part of chromosome 5 is missing
  • "Cat cry" syndrome
  • Characteristic high-pitched cry
  • Small head with round face, small jaw, wide nose, widely separated eyes, ears set low in the head
  • Mental and physical development retardation