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Biology 11-4 Meiosis 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. _____________________—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 ____________________ 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 __________________ ____________________