L20: Anomalies of chromosome structure Flashcards
What can structural chromosome anomalies be caused by
- translocation : reciprocal and robertsonian
- deletions
- duplication
- inversions
What are the 3 causes of Down syndrome
- trisomy 21
- Robertsonian translocation
- somatic mosaicism- non disjunction in mitosis
What is robertsonian translocation
When acrocentric fusion occurs so long arms of two non homologous chromosome join together and short arms are lost
When does robertsonian translocation occur
During paring of homologous chromosomes in meiosis
Why type of chromosomes undergo robertsonian translocation
Acrocentric chromosomes of 13,14,15,21,22
What is reciprocal translocation
When fragments of two non-homologous chromosomes exchange
What chromosomes does reciprocal translocation occur with
All chromosomes not just acrocentric
How does reciprocal translocation occur
When a balanced reciprocal carrier passes it to offspring
What are the outcomes of a balanced reciprocal parent with normal parent
- normal
- carrier
- partial monosomy (lethal)
- partial trisomomy (lethal)
What are the outcomes of robertsonian carrier parent with normal parent
- normal
- carrier
- monosomy 21 (lethal)
- trisomy 14 (lethal)
- monosomy 14 (lethal)
- trisomy 21
When does deletion and duplication occur in chromosomes
During crossing over in meiosis one when there are repeated sequences
How often is deletion and duplication in chromosomes
It is very rare and is usually a one off event
If a family has had a child with cru-di chat syndrome (deletion and duplication anomaly disorder) what are the chances of another child with the same
- very small
If a deletion/duplication occurs twice in a family what are the likely causes
Gonadal mosaicism ( half normal and half mutated gonads)
What is fetal karyotyping
Looking at the fetus karyotype by chorionic villus sampling at 11 weeks of pregnancy to determine whether the baby has an unbalanced or balanced pattern of chromosome
