structural chromosome abnormalities

inversion

piece of chromosome is removed flipped and re-inserted

1. pericentric → involves the centromere

2. paracentric → doesn’t involve the centromere

may lead to fusion genes

translocation

• chromosome is broken and rejoined in the wrong combination

• no issues if genetic material is not lost

reciprocal translocation → between non-homologous chromosomes

deletion

1. interstitial → occurs within the chromosome

2. terminal → occurs near the end → cri du chat syndrome recurrent deletion of P arm of chromosome 5

robertsonian translocation

common in acrocentric chromosomes → centromere is very close to 1 end of the chromosome

ex: 13, 14, 15 , 21,22

1. 2 acrocentric chromosome fuse and the P arms are discarded

2. asymptomatic as P arm has very little coding DNA

21/14 robertsonian chromosome → trisomy 21

isochromosome

chromosome splits in the wrong way (transverse) causing P arms and Q arms to be on seperate chromosomes

1. causes issues except for Xi (facultative chromosome)

ring chromosomes

ends of chromosome fuse due to telomeres being removed → mitotically stable → doesn’t cause uneven crossing over or slipped strand misspairing

but does cause gene deletion at both ends