During which phase of meiosis does crossing over occur? (a)metaphase i (b)metaphase ii (c)prophase i (d)prophase ii

C: Prophase 1

Crossing over occurs in the first division of meiosis. Crossing over of chromatid pair occurs in PACHYTENE stage of PROPHASE I.

The crossing over is the exchange of genetic material. The crossing over takes place due to exchnage od DNA segments between non sister chromatids of homologous chromosomes. This results in new allelic combinations in daughter cells.

you are certainly talking about this picture:

a: is the label of the white square, it is showing the  replication fork, formed by helicase (d) ==> so it is the site of dna separation and replication 

b: is a new dna brand that is following directly the replication fork, so it is continuous ==> built continuously from 5' to 3

c: dna polymerase cannot replicate dna on its own, it needs the of their proteins, and one of them plays the role of a clamp which fixes  the dna with the dna template and increases  the processivity of the enzyme. ==>   stops polymerase from falling off the  template.

d: is the enzyme responsible for forming the replication fork (helicase) ==> unwinds and separates dna into two strands

e: is the delayed strand, it is built  in the opposite sense of the helicase, so dna will be built in fragments ==> built  fragments from 5' to 3 joins

and finally f: is the enzyme that builds  the new dna strand (dna polymerase) ==>   adds nucleotides to make a new dna helix.

credit: gradman555p98x9p

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