Chromosome Disorders

Classification of genetic disorders  Single-gene disorders (2%)  Chromosome disorders (<1%)  Multifactorial disorders (60%)

Types of Mutation class of mutation mechanismfrequencyexamples Genomechromosome missegregation / cell division aneuploidy Chromosomechromosome rearrangement / cell division trans- locations Genebase-pair mutation / cell division point mutations

Chromosome disorders accounting for about half of all spontaneous first-trimester abortions affecting about 1% liveborn infants Chromosome Mutation Genome Mutation

Chromosome Mutation abnormalities of chromosome structure Unbalanced rearrangements (sick) deletions, duplications Balanced rearrangements (healthy) inversions, translocations

Unbalanced rearrangements

Balanced rearrangements

Genome Mutation abnormalities of chromosome number due to nondisjunction (chance occurrence) euploid – an exact multiple of the haploid chromosome number Aneuploidy – trisomy, monosomy Polyploidy – triploid (3n), tetraploid (4n)

Down syndrome (ultrasound examination)

Down syndrome

Turner syndrome

Klinefelter syndrome

Literature Biology, eighth edition, Campbell, Reece Unit three: Genetics Chapter 15: The Chromosomal Basis of Inheritance Concept 15.4: Alterations of chromosome number or structure cause some genetic disorders Pages 297 – 300