11.5 Chromosome segregation

Question 1

Segregation of condensed chromosomes depends on __________________

Answer 1

Centromeres

Question 2

Segregation of condensed chromosomes depends on centromeres

Answer 2

During anaphase of mitosis and meiosis II, sister chromatids must segregate to different daughter cells
During anaphase of meiosis I, sister chromatids do not separate and homologous chromosomes segregate to different daughter cells

Question 3

What are the two functions of centromeres?

Answer 3

1. Hold sister chromatids together (through action of cohesin)
2. Attachment sites for chromosome segregation machinery (through formation of kinetochore)

Question 4

The centromeres of higher eukaryotes are larger and more complex:

Answer 4

Consist of tandem repeats of noncoding satellite DNAs
Repeats of 5 – 300 bp long, can extend over megabases

Question 5

Kitetochores assemble at centromeres:

Answer 5

Chromosomes attach to microtubules of the mitotic spindle at the kinetochore.
Chromatin is packaged differently at the centromere
H3 is replaced by the histone variant CENP-A
CENP-A nucleosomes act as scaffolds for many kinetochore proteins.

Question 6

What is the action of cohesion during mitosis

Answer 6

Cohesion is a protein complex that holds sister chromatids during metaphase
At anaphase, cohesin is enzymatically cleaved and sister chromatids are released from each other

Question 7

Action of cohesion during meiosis I:

Answer 7

At anaphase I, cohesion along chromosome arms is enzymatically cleaved but cohesion at centromeres is not cleaved
Shugoshin protects centromeric cohesion from degradation

Question 8

Action of cohesin during meiosis II:

Answer 8

After entry into metaphase II, shugoshin is removed and centromeric cohesin is degraded