Topic 4-3 Flashcards
what are the two main causes of genetic variation in meiosis?
1) random segregation of chromosomes
2) crossing over/ homologous recombination
random segregation of chromosomes and crossing over occur during:
meiosis I
what are the two main phases of random segregation of chromosomes?
- reduction division
- equational division
true or false: segregation of chromosomes and crossing over occur simultaneously
true
_________ are part of the synaptonemal complex
cohesin complex proteins
at least one crossover is necessary in every homologous choromosome pair for them to:
properly separate during meiosis I
exchange is between homologous DNA molecules during crossover
homologous recombination
what are the two main models of homologous recombination?
1) holliday junction and single-strand break
2) the double-strand break model of recombination
what are the seven main steps of the holliday model of homologous recombination?
1) homologous chr line up
2) a single strand in each molecule breaks and each end migrates to the other DNA molecule
3) each strand joins the broken strand of the other DNA molecule, creating a holliday junction
4) branch migration
5) invert stands to create a branch point
6) rotate the bottom half of the structure
7) cleavage of the horizontal or vertical plane
what are the two potential outcomes of the holliday model?
- noncrossover recombinants
- crossover recombinants
what are the eight major steps of the double-strand break model?
1) two homologous chr align
2) a double strand break occurs in one chr
3) ssDNA is produced on each side
4) a free 3’ end invades the unbroken DNA
5) the 3’ end elongates, displacing the unbroken DNA
6) the displaced strand pairs with the broken DNA
7) DNA synthesis
8) strand attachment creates 2 holliday junctions which can be separated by cleavage and reunion
true or false: in meiotic cells, interphase can be broken down into the G1, S, and G2 phases
false, there is no G2 phase
