12. Prophase I

What is the first stage of meiosis similar to?

First stage of mitosis

What happens first in prophase that is the same as mitosis?

DNA condenses (shorter + thicker) forming chromosomes, chromatids become visible, In animal cells -> centrioles move to opposite poles of cell, Protein microtubules form from each centriole + the spindle develops extending pole to pole

Describe synapsis

Paternal + maternal chromosomes associate as homologous pairs, each pair being called a bivalent

What is the process where paternal + maternal chromosomes associate as homologus pairs?

Synapsis

What does each bivalent have?

4 strands -> 2 chromosomes with 2 chromatids each

What do the chromatids in bivalents do?

Wrap around each other then partially repel each other -> remain joined at certain points though

What do you call the points where chromatids are joined?

Chiasmata

What is the chiasmata?

The points where chromatids touch

What happens at the chiasmata?

Chromatids may break + recombine with different but equivalent chromatids

What is a source of genetic variation?

Swapping of pieces of chromosomes -> crossing over

What is crossing over?

Swapping pieces of chromosomes, which is a source of genetic variation

What happens at the end of prophase I?

Nuclear membrane disintegrates + nucleolus disappears