Cytogenetics• Human Chromosomes• Karyotypes• Variations in
Chromosome number• Variations in
chromosome structure• Genomic imprinting/
Uniparental disomy
Karyotypes
Karyotypes
Karyotypes
Chromosome Painting
Variations in Chromosome number
• Polyploidy = change in Chromosome sets
• Aneuploidy = Change in chromosome number
• Monosomy = (2N -1)• Trisomy = (2N + 1)• Polyploidy = change in
Chromosome sets
Frequency
Triploid
• Triploid = dispermy ususally, 1/10,000 live births• Tetraploid = no cytoplasmic division, sometimes
mosaics
Aneuploidy
MI non-disjunction MII non-disjunction
Trisomy
Trisomy
Trisomy 18 - Edwards
Trisomy 13- Patau
Trisomy 21
Trisomy 21
Sex Chromosomes
Changes in Chromosome structure
• Deletions• Translocations
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Genomic imprinting• Imprinting of chromosomal
regions/genes retain memory of parental origin
• Affects 4p,8q, 17p 18q,22q• Chemical modification of DNA• Occurs before or during
gamete formation• Receive copies from both
parents• Release in embryonic
development• Male chromosomes need to
reimprinted in females
Uniparental Disomy• Chromosome 15q• Prader-Willi syndrome
40% of cases involves disomy = obesity, uncontrolled appetite, mental retardation, both from mother
• Angelman syndrome = both from father, puppet like movements, seizures of laughter
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