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45 Cards in this Set
- Front
- Back
what happens to chromosomes in meiosis |
cell division reduces chromosome number by 1/2 |
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each daughter cell receives ____ of each homologous chromosome |
one copy |
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two main purposes of meiosis |
1. cell division to reduce # of chromosomes by one half
2. crossing over is used to increase genetic diversity of gametes produced |
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crossing over |
exchange of corresponding DNA segments bw homologous chromosomes |
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in crossing over, it is a _____ exchange |
equal |
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give overview of meiosis in 3 steps |
1. homologues pair 2. 1st division: 2n cell divides to give two 1n cells 3. 2nd division: each 1n cell divides to give total of four 1n cells |
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prophase I is subdivided into 5 stages. name them. |
1. leptotene 2. zygotene 3. pachytene 4. diplotene 5. diakinesis |
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way to remember 5 subdivisions prophase 1 |
"He lepto over the zygo in pachystan diplo times. Then he diakinesis. He was just a tene." |
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leptotene |
chromosomes begin to condense |
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zygotene |
homologous chromosomes begin to pair, synapsis |
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synapsis |
pairing of homologues |
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what stage does synapsis occur |
zygotene of prophase I |
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pachytene |
tetrad or bivalent sometimes visible |
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bivalent |
pair of synapsed chromosomes |
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tetrad |
4 chromatids in synapsis |
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diplotene |
-synapsed chromosomes start to separate -homologues remain together at chiasmata |
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chaismata |
apparent point of crossing over |
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diakinesis |
-homologue segments that are not connected by chiasmata move further apart -spindle begins to form -nuclear envelope breaks down |
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metaphase I |
-bivalents orient at metaphase plate w/ centromeres of homologues on opposite sides of plate |
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anaphase I |
-chiasmata break down -homologous chromosomes move to opposite poles |
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telophase I |
-spindle breaks down -cell divides (two 1n cells) |
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what are 4 things to remember between meiosis I and meiosis II? |
1. no DNA replication occurs 2. nuclear envelope may reform transiently 3. chromosomes may decondense briefly 4. meiosis II resembles mitosis, but it starts haploid 1n and sister chromatids are generally not identical bc of crossing over |
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prophase II |
-spindle begins to form -if chromosomes decondensed, they recondense -if nuclear envelope formed, it breaks down |
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metaphase II |
chromosomes align at metaphase plate |
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anaphase II |
-centromeres divide and chromatids move to opposite poles |
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telophase II |
-cytokinesis occurs -spindle disappears -nuclear envelope reassembles |
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most important thing to remember about ploidy of meiosis |
4 haploid (1n) cells, that are not identical |
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meiosis that produces male gametes |
spermatogenesis |
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3 facts about spermatogenesis |
1. DNA may "hypercondense" 2. sperm meiosis is relatively brief 3. two of the four 1n gametes may bud from earlier cell as a means of dumping cytoplasm |
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meiosis that produces female gametes |
oogenesis |
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product of oogenesis |
oocyte |
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how many oocytes are produced? what are they composed of? |
one
a lot of cytoplasm and most stuff needed for early embryonic development |
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what are the other 1n cells called that are not the oocyte?
what do they do/what is their purpose? |
polar bodies
dump extra chromosomes |
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oocytes can often ____ in an earlier stage |
arrest, sometimes for decades |
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the polar body many not ______. Doe is in humans? |
divide
it does not divide in humans |
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which gets majority of the cytoplasm, the polar body or the oocyte? |
the oocyte |
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mitosis vs. meiosis
1. reduces ploidy 2. # cells produced 3. homologues pair 4. division reducing # of chromosomes by half 5. produces identical daughters 6. produces germ cells 7. produces somatic cells |
1. meiosis only 2. mit: 2, mei: 3 or 4 3. meiosis only 4. meiosis I 5. mitosis 6. meiosis 7. mitosis |
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principle of segregation |
hereditary determinants separate in such a way that each gamete is equally likely to inherit either member of the pair |
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oogenesis and stops in what phase |
late prophase I, between diplotene and diakinesis |
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in humans, meiosis begins... |
during field development, when fetus is forming |
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meiosis I isn't completed in humans until... |
ovulation, when period starts and oocyte is ready to ovulate |
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meiosis II isn't completed in humans unless... |
fertilization occurs |
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in mitosis, daughters are identical unless.. |
mutation or mitotic recombination |
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independent assortment |
unlinked genes assort independently from one another |
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in independent assortment, what do the products depend on? |
metaphase I alignment of chromosomes (all outcomes are equally likely) |