3.3 Meoisis

define: meiosis

reduction division of one diploid nucleus to form four haploid nuclei

define: homologous chromosomes

chromosomes that are similar in size/shape, same sequence of genes, not necessarily alleles of those genes

define: crossing over

exchange of DNA material/alleles between non-sister chromatids
(during prophase 1 of meiosis)

define: chiasmata

x-shaped structures formed at the point at which non-sister chromatids intersect during crossing-over

identify where in meiosis or cell cycle the following events occur: DNA Replication, Crossing Over, Formation of Chiasmata

S-phase of interphase
Prophase 1
Prophase 1

identify where in meiosis or cell cycle the following events occur: random orientation of bivalents, separation of homologous chromosomes, separation of sister chromatids

metaphase 1, anaphase 1, anaphase 2

Summarize the Events that occur in prophase 1 and interphase

* DNA is replicated in interphase prior to meiosis 1 so all chromosomes consist of two sister chromatids
* homologous chromosomes pair up/synapse in prophase 1, forming bivalents
* crossing over in prophase 1, forming chiasmata resulting in exchange of genetic material/alleles between non-sister chromatids in prophase 1

summarize meiosis 2

* chromosomes line up along the equator in metaphase 2
* separation/movement of sister chromatids to opposite poles in anaphase 2
* uncoiling/nuclear membrane reforms telophase 2
* four haploid cells/nuclei/gametes formed at the end of meiosis 2

similarities mitosis and meiosis

both mitosis and meiosis 1 are preceded by s phase/ dna replication (no s phase precedes meiosis 2) sister chromatids separate in both mitosis and meiosis 2 -> chromosome behavior in meiosis 2 and mitosis is similar

described how chiasmata are formed in meiosis

* chiasmata formed during prophase 1 of meiosis at position where crossing over occurred, where non-sister chromatids intersect during crossing-over
* homologous chromosomes pair together, known as synapsis non-sister chromatids break, cut at same point
* non-sister chromatids join up, exchanged sections of DNA/alleles

chiasmata's structure & function

X shaped structures stabilize homologous chromosomes, bivalents through metaphase 1 until anaphase 1 allow for exchange of alleles between non-sister chromatids

explain crossing over in prophase 1

crossing over leads to the exchange of alleles between non-sister chromatids, maternal and paternal chromosones leading to new combo of alleles on the chromosones of haploid gametes produced by meiosis point where crossing over occurs is random occurs at least once and between different chromatids in pair can separate linked genes

explain random orientation in metaphase 1

* orientation of bivalents on equator during metaphase 1 is random orientation of one pair is independent of others means maternal/paternal chromosome could move to either pole
* random assortment, separation of alleles where combination of alleles seen in the parents are broken up resulting in unique combo of alleles in haploid cells produced by meiosis
* 2^n combos

explain fusion of gametes

* fertilization is random, brings together genes/alleles from two parents
* fertilization generates new combos of genes/alleles due to segregation of alleles during meiosis
* many new possible combination of male/female gametes

Similarities between Meiosis 1 and Meiosis 2

Can only occur in eukaryotes
G phase of interphase usually occurs first
Production of daughter cells based on parent cell’s genetic material
Four phases occur : PMAT

Differences between Meiosis 1 and Mitosis 2 (diploid/haploid)

Meiosis 1: starts at diploid, ends as haploid
Meiosis 2: starts at haploid and ends as haploid

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Explain how Sexual Reproduction produces variation (Crossing Over in Prophase 1)

* Crossing over leads to the exchange of alleles between non-sister chromatids / maternal and paternal chromosomes;
* leading to new combinations of alleles on the chromosomes of haploid gametes produced by meiosis;
* point where crossing-over occurs is random;
* occurs at least once and between different chromatids in the pair;
* can also separate linked genes;

Similarities Meiosis and Mitosis

* Both mitosis and meiosis take place in the cell nuclei, which can be observed under a microscope.
* Both mitosis and meiosis involve cell division.
* Both the processes occur in the M-phase of the cell cycle.
* In both cycles, the typical stages are prophase, metaphase, anaphase and telophase.
* In both cycles, synthesis of DNA takes place.

Differences Mitosis/Meiosis

homologous chromosomes separate only in meiosis I / chromosome behavior in meiosis I and mitosis is different;

Summarize the events of metaphase 1, anaphase1, telophase 1

movement of pairs of homologous chromosomes/bivalents to the equator in metaphase 1

random orientation of bivalents along equator

separation/movement of one homologous chromosomes from each pair to opposite poles in anaphase 1

two haploid cells/nuclei formed at the end of meiosis 1

Differences between meoisis1, meiosis 2 (crossing over)

Meiosis 1 :crossing over may occur during prophase 1 to create genetically divergent sister chromatids Meiosis 2 : crossing over does not happen

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Differences between meoisis1, meiosis 2 (Division)

Meiosis 1 : reduction division Meiosis 2: is akin to mitotic division (but of haploid cells)

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Differences between meoisis1, meiosis 2 (replication)

Replication of DNA prior to Meiosis 1, No DNA replication takes place in Meiosis 2

Differences between Meiosis 1/2 (mitoisis)

Meiosis 1: Does not resemble mitosis Meiosis 2: resembles mitotic process

Differences mitosis/meoisis (division)

two divisions in meiosis, only one in mitosis / mitosis produces 2 cells, meiosis 4 cells;

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Differences mitosis/meoisis (haploid)

meiosis results in haploid cells, mitosis in diploid cells;

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Differences mitosis/meiosis (variation/identical)

mitosis produces cells that are identical to each other and the parent cell, meiosis produces cells with genetic variation that are not identical to each other;

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Differences mitosis/meiosis (crossing over)

crossing over / chiasmata formation only occurs in meiosis;

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Differences mitosis/meiosis (homologlous chromosones)

homologous chromosomes move to the equator in pairs only in meiosis;

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Differences mitosis/meiosis (what it produces)

mitosis produces cells for growth, tissue repair and asexual reproduction, meiosis produces gametes;