Week 5_Meiosis in more detail Flashcards
what are the phases of meiosis?
interphase (G1, S, G2)
1 diploid cell –> 2 chromatids/chromosome
meiosis I (reduction division):
- prophase I
- metaphase I
- anaphase I
- telophase I
2 haploid cells –> 2 chromatids/chromosome
- homologous chromosomes are segregated
interkinesis (a rest period)
meiosis II:
- prophase II
- metaphase II
- anaphase II
- telophase II
sister chromatids are segregated
4 haploid cells –> 1 chromatid/chromosome
what occurs in prophase I?
(1) chromosomes condense
(2) nuclear membrane breaks down
(3) spindle poles begin to form
(4) homologous chromosomes pair up and form a complex called a bivalent or tetrad
homologous chromosomes are held together in bivalents/tetrads by ___
synaptonemal complex proteins
what is crossing over?
in a bivalent, genetic material can be exchanged b/n paired chromosomes
crossing over ___ chromosomes and increases ___
rearranges chromosomes
increases genetic variation
crossing over may occur ___ times along chromosomes
multiple
crossing over only occurs during ___ when ___ are paired
prophase I
when homologs are paired
what occurs during metaphase I?
(1) homologous pairs line up at the metaphase plate
(2) alignment of homologs on either side of the metaphase plate is random
what does independent assortment ensure in metaphase I?
ensures each new cell contains a mixture of homologs from the mother and father leading to greater genetic diversity
what occurs during anaphase I?
(1) synaptonemal complex proteins dissolve
(2) homologs separate
(3) homolog segregated to opposite spindle poles by kinetochore microtubules
what occurs during telophase I?
(1) chromosomes begin to decondense
(2) spindle network breaks down
(3) nuclear membranes re-form
(4) cytokinesis divides the cell
(5) meiosis I is completed
(6) interkinesis
what is interkinesis?
a period of rest in preparation for Meiosis II
Meiosis I (features/reviews):
cell goes thru PMAT I
homologs pair up to form ___ during ___
bivalents/tetrads
prophase I
bivalents are held together by ___
synaptonemal complex proteins
during crossing over, an exchange of DNA occurs between ___
homologs
during crossing over, ___ occurs between homologs
an exchange of DNA
in metaphase I, homologous pairs ___ (___)
align
independent assortment
in anaphase I, homologs ___
separate and are segregated
the result of meiosis I is…
2 haploid cells
2 chromatids/chromosome
at the beginning of meiosis II, there are…
2 haploid cells
2 chromatids/chromosome
is there any DNA replication in meiosis II?
no
during meiosis II, cell goes thru ___
PMAT II
during anaphase II…
sister chromatids segregate
what is the result of meiosis II?
4 haploid cels
1 chromatid/chromosome
cell prior to S-phase:
- haploid or diploid?
- 2 chromatid or 1 chromatid chromosomes?
diploid
1 chromatid chromosomes
after S phase but prior to Meiosis I:
- haploid or diploid?
- 2 chromatid or 1 chromatid chromosomes?
diploid
2 chromatid chromosomes
after Meiosis I prior to Meiosis II:
- haploid or diploid?
- 2 chromatid or 1 chromatid chromosomes?
haploid
2 chromatid chromosomes
after Meiosis II:
- haploid or diploid?
- 2 chromatid or 1 chromatid chromosomes?
haploid
1 chromatid chromosomes
