Meiosis and genetic variation Flashcards
what is meiosis?
division of the nucleus of cells
produces 4 daughter nuclei, each with half the number of chromosomes as the parent cell
what happens during sexual reproduction
two gametes fuse to give rise to new offspring
why does the number of chromosomes have to be halved as some stage in the life cycle?
to maintain a constant number of chromosomes in adults of a species.
how many nuclear divisions occur in meiosis?
2
what happens in the first nuclear division (meiosis 1)?
- the homologous chromosomes pair up
- chromatids wrap around each other and portions are exchanged (CROSSING OVER)
- the homologous pairs are separated
- by the end of the stage, 1 chromosome from each pair is in 1 of 2 daughter cells
what happens in the second nuclear division (meiosis 2)?
- the chromatids move apart
* at the end 4 cells have been formed- containing 23 chromatids
during which division can genetic variation occur?
meiosis 1
what two ways can genetic variation occur?
independent segregation of homologous chromosomes
crossing over- recombination homologous chromosomes
what is a locus?
one of the different forms of a particular gene
what is independent segregation?
chromosomes line up alongside its homologous partner
when they arrange themselves they do it randomly- which one of each pair goes to the daughter cell and with which one of the other pairs depends on hw they are lined up.
what is crossing over?
- chromatids become twisted, tensions are created and portions of the chromatids break off.
- these portions re-join with the chromatids of the homologous partner
- new genetic combinations are produced
what is the process of the portions of the chromatid recombining with another chromatid?
recombination
