Download 11-4 Meiosis - Laurel County Schools

Biology 11-4 Meiosis
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Gregor Mendel did not know where the _____________ he had discovered were _________________.
However, his _____________________ of how genes should behave were so ____________ that it was not
long before biologists were certain they had found them—____________ are located on
______________________ in the cell _______________.
Mendel’s principles of genetics require at least 2 things:
o Each organism must ________________ a single _____________ of every gene from each of its
“_______________”
o When an organism produces its own ________________, those _____ sets of _______________
must be __________________ from each other so that each __________________ contains just
____________ set of ____________
 This means that when _________________ are formed, there must be a
________________ that separates the 2 sets of genes so that each gamete ends up with
just ___________ ____________.
 Mendel did not know it, but this is _____________ what happens!
Chromosome Number
 In order to examine this process, let us use the ___________ ___________ as an example
o Adult fruit fly body (________________) cells have ______ chromosomes
 ____ from __________
 ____ from __________
o These _____ sets of chromosomes are ___________________, meaning that each of the _____
________________________ from one parent has a corresponding chromosome from the
_____________ ______________.
 Diploid—__________________________________________________________________, means
“____________ ___________”
o Represented by _______
o For fruit flies, _____= _____ or the __________ number for fruit flies is ______.
o _________________ cells contain 2 ________________ ___________ of chromosomes and,
therefore, _____ complete ___________ of ____________
 ________________—a cell (usually _______________ or _________ cells) that contain only one set of
______________________ (one set of ___________), means “_________ ___________”
o Represented by _____ or ______
o For fruit flies, _____= ______ or the _____________ number for fruit flies is __.
o _________________ cells contain ____________ complete set of ________________________
and, therefore, one ______________ ___________ of genes.
Phases of Meiosis
 This is the process that produces _______________ (______) ________________ from ________________
(______) cells
 __________________—a process of reduction division in which the number of chromosomes per cell is cut
in half through the separation of homologous chromosomes in a diploid cell
o Involves ____ distinct _______________, called __________________ and
_____________________
o At the end of _________________, the ______________ cell that entered meiosis has become
____ ________________ cells
 NOTE: when discussing or writing about the phases of meiosis, it is IMPERATIVE that you use I or II
after the word meiosis!! If you do not do this, the person listening or reading does not know which stage
you are referring to.
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_____________________—Prior to meiosis I, cells undergo a round of _______
______________________, forming ____________________ chromosomes.
o The cells then begin to ____________________ in a way that looks similar to
__________________.
Meiosis I
o ________________________
 ____________ _________________ breaks down
 Each ________________________ pairs with its corresponding
_________________________ chromosome to form a ______________. (There are
_____ ____________________ in a ________________).
 As homologous chromosomes ____________ up and form _______________, they
exchange portions of their _______________ in a process called _________________________________.
 ________________-_____________ results exchange of ________________
between homologous chromosomes and produces new ___________________ of
alleles.
o __________________________
 ___________________ __________________ attach to the chromosomes.
o __________________________
 The _______________ are pulled apart into individual _______________________.
 _____________________ fibers pull the homologous ________________ toward
___________________ ends of the cell.
o ___________________________ and _________________________
 __________________ _______________________ form
 The cell ____________________ into _____ cells that are ________________ (they
have _________ the number of ____________________ that the original cell did)
 Because each _____________ of homologous chromosomes was
______________________, neither of the _________________ cells has the ______
complete __________ of chromosomes that it would have in a ___________________
cell.
 These ____ sets have been _________________ and sorted almost like a deck of
cards.
 The 2 cells produced by _____________________ have sets of chromosomes and alleles
that are _______________ from each other and from the __________________ cell that
entered ___________________
Meiosis II
The _____ cells produced by _______________ now enter a second ________________
__________________.
Unlike the first ________________, NEITHER CELL UNDERGOES A ROUND OF
_______________________ _________________________ before entering ____________________.
o ___________________________
 _______________ _________________ breaks down
o __________________________
 ________________________ line up in a way similar to metaphase of
____________________.
o ____________________________
 _____________ _________________ separate and ______________ towards
___________________ ends of the cell
o ______________________ and _______________________
 ___________________ ____________________ re-forms
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____________________ results in _____ _______________ _________________
_____________
Gamete Formation
 In _______________ animals, the _____________ gametes formed are called ____________
 In ______________ animals, the haploid ______________ formed are called ____________ or
__________________
o Usually only ___________ of the cells produced by meiosis is used in
_______________________.
o The other _____ are _______________ ________________ and they usually do not
_______________________
o There are basically 2 reasons for this
 The __________________ at the end of meiosis I and II are ________________, so that
the egg receives a __________________ portion of the ____________________
 The ____________ needs this extra __________________ in order to
__________________ the growing organism once the egg is
____________________________
Comparing Mitosis and Meiosis
 The words sound alike, but the processes are quite different
 __________________ results in the production of 2 genetically identical diploid cells (2n)
o Allows an organism’s body to ____________ and __________________ cells
o In __________________ reproduction, a new organism is produced by ________________ of
the cell or cells of the _________________ organism
 __________________ results in the production of 4 genetically different haploid cells (1n)
o Allows _________________ reproducing organisms to produce ______________
o Thus, meiosis is involved in __________________ ____________________