Explain how the reduction and rearrangement are accomplished in meiosis. (5 pts max)



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Meiosis Essay Answer Key

Meiosis reduces chromosome number and rearranges genetic information.



  1. Explain how the reduction and rearrangement are accomplished in meiosis. (5 pts max)

Reduction:

1 point: (homologous) chromosomes pair then separate and move to opposite poles during 1st meiotic division

1 point: chromatids separate during 2nd meiotic division

Or

1 point: two rounds of cell (nuclear) division but only one replication of the chromosomes


Rearrangement:

1 point: crossing over (in proper context)

1 point: random alignment (independent assortment) of tetrads

1 point: elaboration (eg correct mechanism, description or consequences of one of the above)




  1. Describe in detail the process of meiosis as it occurs in an organism with a diploid chromosome number of 4 (2n = 4). Include labeled diagrams in your discussion (7 pts max)

General


1 point: reduces chromosome number in half
Prophase I

1 point: homologous chromosomes pair up to form tetrads


Metaphase I

1 point: tetrads line up at the middle of cell


Anaphase I

1 point: homologous chromosomes are separated by spindle fibers


Telophase I and cytokinesis:

1 point: nuclear envelope reforms and cytoplasm splits to form 2 haploid cells


Prophase II

1 point: chromosomes condense

or

1 point: nuclear envelope disappears


Metaphase II

1 point: chromatids line up at the middle of cell


Anaphase II

1 point: chromatids are separated

Telophase II and cytokinesis:

1 point: nuclear envelope reforms and cytoplasm splits to form 2 haploid cells




  1. Indicate when and how crossing over occurs in meiosis. (2 pts max)

1 point: occurs during prophase I of meiosis I



1 point: homologous chromosomes synapse and can exchange genetic material

1 point: chiasmata is a visible result of crossing over


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