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Name:_______________________________ Date:_____________ Block:_________ Meiosis Fill in the blank notes GENES: Genes determine individual ______________________ Genes do not exist ___________ in the ______________s of a cell; they are lined up on _________________. A chromosome can contain a ______________ or more __________ along its length. In the body, cells of most plants and animals chromosomes occur in _____________. One chromosome in each pair come from the ___________ parent and the other came from the ________________ parent. A cell with two of each kind of chromosome is called a _________________ cell. They are said to contain 2n number of ___________________. Each species of organisms contains a characteristic number of _______________________. Humans have _____________ pairs of chromosomes or ____________ total. WHY MEIOSIS? When cells divide by _________________, the new cells have exactly the ______________ number and kind of chromosomes as the original cell. The body uses meiosis to provide a cell for the purpose of ___________________. A cell produced by meiosis is said to be _______________ and contain n amount of chromosomes This cell is called a _______________. – An example of a gamete is ____________ (in males) and __________ (in females) – Produced by meiosis, gametes have ____________ the number of chromosomes as a parent’s body cell. Meiosis consists of 2 separate _________________, known as meiosis ____ and meiosis ________. Meiosis I begins with one _______________ (2n) cell. (just like mitosis). By the end of meiosis II there are ________ haploid (n) cells. (this is different then mitosis). When a haploid (n) sperm cell _______________ a haploid egg (n) cell, the resulting cell (called a zygote) once again has a _________________ (2n) number of cells. 1 The Phases of Meiosis ____________________ ____________________ ____________________ ____________________ ___________________ ____________________ ____________________ ____________________ ____________________ MEIOSIS I: INTERPHASE I Similar to ______________ The cell _______________ its chromosomes. After replication each chromosome consists of 2 identical ____________ chromatids, held together by a _______________. MEIOSIS I: PROPHASE Steps similar to prophase in mitosis: – The DNA of the chromosomes __________ up. – Centrioles migrate to opposite ______________ of the cell. – The ______________ apparatus forms – The nuclear envelope begins to ________________ Steps different than prophase in mitosis: – As the DNA coils, _______________________ chromosomes line up with each other, gene by gene along their length, to form a four-part structure called a __________________. Homologous chromosomes have genes for the ____________ trait, such as height. A tetrad consist of two homologous chromosomes, each made up of two sister chromatids. The chromatids in a tetrad pair so tightly that ________________________ can occur. Crossing over is when non-sister chromatids from homologous chromosomes ____________ and _________________ genetic material. Crossing over: – There are an average of _________ to __________ crossovers for each pair of homologous chromosomes – Crossing over aids in genetic _______________. 2 MEIOSIS I: METAPHASE I The _____________________ of each chromosome become attached to a spindle fiber The spindle fibers pull the ____________________ into the middle or equator, of the spindle. – this is different then in mitosis: In meiosis the homologous chromosomes are lined up side by side as _______________. In mitosis chromosomes line up on the spindle’s equator ____________________ of each other. MEIOSIS I: ANAPHASE I ____________________ chromosomes, each with its two chromatids, separate and move to opposite ends of the cells. – The _____________________ holding the sister chromatids together do not split as they do during anaphase in mitosis. MEOSIS I: TELOPHASE I ________________ is broken down Chromosomes _______________ Cytoplasm ________________ to yield two new cells Each cell has _____________ the genetic information as the original cell because it has only ____________ chromosome from each homologous pair. The daughter cells are genetically ___________________ from each other and the parent. Another cell _________________________ is needed because each chromosome is still _____________________. 3 MEIOSIS II: PROPHASE II DNA _____________ A __________________ forms _________________ migrate to opposite poles of the cell. _______________ envelope disintegrates MEIOSIS II: METAPHASE II The ______________________, made up of sister chromatids, are pulled to the center of the cell and line up __________________ at the equator. MEIOSIS II: ANAPHASE II The __________________ of each chromosome splits allowing the sister chromatids to ____________________ and _________________ to opposite poles. MEIOSIS II: TELOPHASE Nuclei _____________ The spindles ____________________ The _________________ divides RESULTS OF MEIOSIS: The events of meiosis II are _________________l to those of mitosis except that the chromosomes do not _____________________ before they divide. At the end of meiosis II, ______________ haploid cells have been formed from ______________ diploid cell. 4