· DNA-ligaas ühendab mahajääva ahela fragmente 4. Tsentromeeride funktsioon, struktuur. (2p) A centromere functions in sister chromatid adhesion, kinetochore formation, and pairing of homologous chromosomes during meiosis, prophase and metaphase. The centromere is also where kinetochore formation takes place: proteins bind on the centromeres that form an anchor point for the spindle formation required for the pull of chromosomes toward the centrioles during anaphase and telophase of mitosis. Improperly functioning centromeres result in the chromosomes that do not align and separate properly, resulting in aneuploidy or daughter cells receiving the wrong number of chromosomes. Aneuploidy can cause conditions such as Down syndrome if the cells survive at all. The centromeric DNA is normally in a heterochromatin state, which is essential for the recruitment of the cohesin complex that mediates sister chromatid cohesion after DNA replication as well as
[5] 113. (i) Q, S, P, N, M, R ; 1 (ii) accept correct names of stages Q; A prophase 1 M; A anaphase 2 Q / S ; A prophase 1 / metaphase 1 S; A metaphase 1 R; A telophase 2 5 (iii) DNA replication ; synthesis of proteins / named protein ; A transcription / translation synthesis of membrane ; synthesis of, organelle(s) / named organelle ; respiration ; AVP ; e.g. centrioles replicate ; 2 max
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