Lecture 7&8: Chromosome Segregation, Aneuploidy & Non-Dysjunction Flashcards
What is the centromere?
Region of DNA which is the main attachment site between sister chromatids, and is where kinetochores form to attach to spindle
What is cohesin?
The protein complex that holds chromatids together, which resists the pulling force of microtubules
What triggers chromosome separation?
Cohesin destruction
How does cohesin initiate separation?
4 subunits form a ring to hold chromatids together, 1 subunit is destroyed by protease when anaphase starts
When is cohesin established and destroyed l?
Established: S phase
Destroyed: meta/anaphase
What are the steps of meiosis I?
- homologous chromosomes pair eachother
- DNA exchange via crossing over and recombination
- chromosomes separate into 2 haploid cells
What are the steps of meiosis II?
- sister chromatids are separated
- produces 4 haploid gametes
In what ways can meiosis create diversity?
- segregation of homologous chromosomes
- recombination between homologous chromosomes
What is the aim of prophase I?
To recombine homologous chromosomes
What is the synaptonemal complex?
Structure formed by chromatids to facilitate crossing over, which stabilises pairing of homologous chromosomes and promoting recombination
What are the stages of synaptonemal complex formation after interphase?
Leptotene: SC starts forming
Zygotene
Pachytene: SC fully formed
Diplotene: SC disassembled
Diakinesis: chromosomes condense
Why are chiasmata?
Points where chromosomes are held together after crossing over
What happens if centromeric cohesin is not protected during meiosis I?
- homologous chromosomes are segregated properly
- sister chromatids are separated prematurely
What causes maternal age effects?
Cohesin fatigue hypothesis: As cohesin is established in S phase, the same molecules are on chromosomes for decades, may explain effects
