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