Chapter 11 Flashcards
what is meiosis?
the division of a diploid parent cell into 2 haploid daughters
what is a diploid in meiosis?
homologous pairs
what is a haploid in meiosis?
half of a homologous pair
what are gametes?
sex cells
why is meiosis important?
it produces genetic variation, which is essential for a population to survive
what is alternation of generations?
some organisms, like fungi and some plants, spend most of their lives as haploid, and only become diploid for a short period of time before returning to haploid form
what is synapsis and when does it take place?
in meiosis I, members of homologous pairs (maternal and paternal) come in close physical contact with each other to exchange genetic information
how many rounds of division does meiosis include?
2; meiosis 1 and meiosis 2
what is the synaptonemal complex?
the structure formed when members of a homologous pair come into contact with each other during synapsis
what is crossing over?
the exchange of genetic material between homologous pair (nonsister chromatids), is totally random, could happen, could not
what is a chiasmata?
the location of the crossing over event
what does crossing over do from an evolutionary standpoint?
increases variation
between which nonsister chromatids does crossing over occur?
recombinant chromatids
what does meiosis do in terms of chromosome number?
reduces chromosome number from diploid to haploid
what does meiosis I separate?
homologous pairs
what does meiosis II separate?
sister chromatids
what does meiosis II yield?
4 cells with 2 replicated chromosomes
what 4 things happen in prophase I of meiosis?
- chromosomes begin to condense
- spindle begins to form
- nuclear membrane breaks down
- synapsis occurs?
what happens in metaphase I of meiosis?
pairs of homologous chromosome line up along the metaphase plate (ATTACHED BY KINETOCHORES), with each member of the homologous pair on opposite sides of the metaphase plate
how does metaphase I of meiosis lead to genetic variation?
there are lots of alignment possibilities for the chromosomes
what happens in anaphase I of meiosis?
kinetochore microtubules shorten, pulling apart HOMOLOGOUS PAIRS, maternal and paternal, NOT sister chromatids
what happens in telophase I?
separated homologues form a cluster at each pole of the cell, nuclear envelope reforms around each daughter cell nucleus
are sister chromatids identical in telophase I? why or why not?
no, crossing over has occurred
what does meiosis II resemble?
a mitotic division
what does prophase II follow?
a brief interphase with no S phase
what happens in prophase II?
spindle apparatus forms in each daughter cell from meiosis I, nuclear envelope breaks down
does the nuclear envelope always reform in telophase I?
no, in some species, it doesn’t reform in telophase I, removing the need for a 2nd breakdown in prophase II
what happens in metaphase II?
there is a completed spindle apparatus in each cell, SISTER CHROMATIDS line up on opposite sides of metaphase plate
what happens in anaphase II?
microtubules shorten, pulling apart SISTER CHROMATIDS to opposite poles of the cells
what happens in telophase II?
nuclear membranes reform around 4 different clusters of chromosomes
what results from telophase II after cytokinesis?
4 haploid cells
are the haploid cells formed after meiosis II identical? why or why not? (2 reasons)
not identical, due to random alignment of homologous pairs in metaphase I and crossing over in prophase I
list the number of chromosomes at each major stage of meiosis, assuming that the original haploid number is 3 chromosomes
- 3 chromosomes in each maternal and paternal cell
- 6 chromosomes in diploid offspring after meiosis I
- 3 chromosomes in each potential gamete after meiosis II
list the 5 differences between mitosis and meiosis
- crossing over only occurs in meiosis, not mitosis
- mitosis produces 2 diploid cells, meiosis produces 4 haploid cells
- mitosis occurs in somatic cells, meiosis occurs in germ (sex) cells only
- the daughter cells of mitosis are genetically identical to the parent cell, but the daughter cells from meiosis feature genetic variation from the parent cells
- there is only one division cycle in mitosis, where meiosis has 2 division cycles
list 3 similarities between mitosis and meiosis
- both start with a diploid parent cell
- in mitosis metaphase, and meiosis metaphase II, sister chromatids align on opposite sides of the metaphase plate
- both utilize cytokinesis, once for mitosis, and twice for meiosis
list the differences between metaphase I and anaphase I in meiosis and metaphase and anaphase in mitosis
metaphase I and anaphase I line up and pull apart members of homologous pairs, while metaphase and anaphase in mitosis line up and pull apart sister chromatids
