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Midterm

Biology 1201A Midterm: Biology1201_Test2Outcomes_Week10
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4 pages41 viewsFall 2016

Department
Biology
Course Code
Biology 1201A
Professor
Vera Tai
Study Guide
Midterm

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Biology 1201 Test 2 Outcomes Part 5
Describe the phases of meiosis and their associated key events and consequences
Prophase I: after condensation, the two chromosomes of each homologous pair come together and line
up side by side (synapsis) the fully paired homologues are called tetrads; genetic recombination
happens here where there is a mixture alleles between the two homologous chromosomes to produces
new combinations and increases the genetic variability
Prometaphase I: the nuclear envelope breaks down and the spindles enter the former nuclear area;
both sister chromatids of one homologue attach to the kinetochore microtubules that leads to one
spindle pole and the sister chromatids of the other homologue chromosome attaches to the
microtubules of the opposite spindle pole
Metaphase I: the recombined tetrads are aligned on the equatorial plane via the movement of the
spindle microtubules
Anaphase I: the two chromosomes are separated via spindle microtubules and each chromosomes is
taken to the opposite spindle poles (there are now haploid number of chromosomes); each
chromosomes still contains 2 sister chromatids at their centromeres
Telophase I & Interkinesis: little or no change to the chromosomes (new nuclear envelope may develop
in some species, but not in others); for interkinesis, the spindle from the first meiotic division
disassembles and the microtubules reassemble into two new spindles for the second division (there is
NO DNA REPLICATION between the first and second division)
Prophase II, Prometaphase II & Metaphase II: in prophase II the chromosomes simply condense; then in
prometaphase II, the nuclear envelope breaks down and the spindle enters the former nuclear area and
they attach to the 2 kinetochores of each chromosome (each spindle from opposite poles attach to one
kinetochore); and then in metaphase II, the spindles line up the sister chromatids at the equatorial plane
Anaphase II and Telophase II: in anaphase II, the sister chromatids separate and move to the opposite
poles; at the end of the sister chromatid separation, they are now called chromosomes (segregated to
opposite poles) and then in telophase II, the chromosomes de-condense to their interphase state and
the spindle dissembles and the nuclear envelope begins to form (there is no DNA replication after
telophase II); the result by the end of 2nd meiotic division is 4 haploid cells that are genetically different
from their parents and it contains half the number of chromosomes that it did before meiosis started
Predict and/or identify the phase in meiosis in which an error occurred based on the resulting daughter
cells
Non-disjunction: one of the pairs or sister chromatids fails to separate this results in
aneuploidy
The gamete could either have an extra chromosome or one less chromosome
If the gamete has one more, then after fertilization, that zygote could have trisomy (3
chromosome; if gamete has one less, then the zygote could have monosomy (1 chromosome)
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