Mitosis and Meiosis Outline
July 11, 2013
7th Grade
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Reasons that a cell divides
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Reproduction, growth and development, __________________________________________.
Cell Division
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Results in genetically ___________________________________daughter cells
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Cells duplicate their genetic material
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This happens __________________________ they divide, ensuring that each
daughter cell receives an exact copy of the genetic material (DNA)
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Genetic Material: DNA
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The DNA in a eukaryotic cell is organized into several linear ___________________________.
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DNA exists as a single, long, double-stranded fiber extending a chromosome’s entire length.
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Chromosomes are composed of a complex of DNA and protein called
____________________________________ that condenses during cell division
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Each unduplicated chromosome contains one DNA molecule, which may be several inches
long
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How replication works
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Each chromosome has a special region of attachment called a _________________________.
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This links sister chromatids together
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In mitosis, this is where the kinetochore attaches to pull chromatids apart from one
another
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Chromosomes
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All species have a characteristic number of chromosomes in all their cells -- this is called the
diploid number and is symbolized as the 2N number
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EX: for humans, 2n = 46; domestic dog, 2N = 78; fruit fly, 2N = 14.
The Cell Cycle
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Interphase
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Cell is growing, replicating DNA, preparing to Divide
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Consists of 3 parts:
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G1- normal metabolism and growth, cell components are synthesized
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S – DNA replication (2N to 4N)
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G2 – growth continues until division begins
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Nucleus is well-defined
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Produce proteins and organelles
Mitosis and Meiosis Outline
July 11, 2013
7th Grade
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M-phase: Mitosis
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Mitosis is the division of the cell’s DNA into 2 daughter cells
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There are 4 phases:
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After Mitosis…there is a process called cytokinesis
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Prophase, Metaphase, Anaphase, and _____________________.
The rest of the cell contents separate so the two new cells can form
What is passed on when a cell divides?
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Mitosis: exact copy of genetic material = DNA is passed
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Cytokinesis: organelles, cytoplasm, cell membrane, and enzymes are passed
Phases of Mitosis
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Prophase
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The chromosomes appear condensed
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By the end of prophase…the nuclear envelope has broken down
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Mitotic spindles go to each pole of cell
Metaphase
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Microtubules from the two spindles attach to kinetochores of centromere
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chromosomes are pulled into a line at middle of cell = equatorial plate
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In human cells, all 46 chromosomes lined up at equatorial plate
Anaphase
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Sister chromatids separate and are pulled to opposite poles of the cell
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Sister chromatids are now chromosomes
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Each pole contains a complete compilation of chromosomes
Telophase
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Nuclear envelope reforms around each set of chromosomes
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Two new nuclei are created
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Chromosomes becoming more diffuse
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Mitosis is now complete, but the cell still needs to physically split itself
Cytokinesis
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Division of the cytoplasmic contents of the cell
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Includes organelles, proteins, and cytoplasm
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Formation of a contractile ring
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When ring contracts, a groove called the cleavage furrow forms
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This groove eventually deepens and the cell is split into two daughter cells.
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Cytokinesis is NOT a part of mitosis
Mitosis and Meiosis Outline
July 11, 2013
7th Grade
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Reproduction
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Cells and organisms display two types of reproduction
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Asexual reproduction -- only one parent and offspring are genetically
identical ("clones") of the parent -- offspring receive exactly the same DNA
instructions as parent has.
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Sexual reproduction -- two parents and offspring have slightly different DNA
message from those of the parents and from other offspring.
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Sexual Reproduction
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new organism begins its life as a single-cell called a zygote.
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a zygote formed is from the fusion of specialized sex cells called gametes
(e.g. sperm and egg).
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each of two parents contributes one _____________________ to the zygote.
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since the zygote is diploid (2N), the gametes that fuse to form it must have
1/2 the diploid number
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gametes are said to be _________________________ (1N)
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human zygote 2N = 46
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human gamete 1N = 23.
Meiosis
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Process underlying sexual reproduction
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Produces the male gamete (sperm) and female gamete (ovum)
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Stages are similar to that of mitosis. However, the division process occurs _________.
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Produces haploid (N) set of cells rather than diploid (2N) cells
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Resulting cells are called ________________________.
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Crossing over (genetic recombination) occurs during meiosis
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Responsible for genetic variation
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Why you are/look different from your parents!!!
Meiosis I
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diploid cell produces 2 _______________________ cells
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reduction division (2N to 1N)
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After meiosis I, although the cell contains 46 chromatids, it is only considered as
being 1N, with 23 chromosomes.
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Separates homologous chromosomes (tetrad)
Phases of Meiosis 1
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Prophase I
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Each chromosome, consisting of two chromatids, lines up side-by side with
its homologue -- this structure is called a tetrad
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Mitosis and Meiosis Outline
July 11, 2013
7th Grade
Crossing over occurs
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Chromatids break apart and reattach to a different homologous chromosome
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Nuclear membrane breaks down
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Spindle fibers formation
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Crossing Over
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Chromatids of homologous chromosomes may randomly exchange
segments
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Metaphase I
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Chiasma – site of crossing over
Tetrads of homologous chromosomes align along equatorial plate
Anaphase I
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tetrads separate -- each chromosome with its 2 sister chromatids goes to an
opposite pole
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Telophase I & Cytokinesis
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Two cells form
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Chromosomes still have sister chromatids
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Nuclear membrane reforms
Meiosis II
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Separates sister chromatids
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Now each step occurs in each of the two cells produced in meiosis 1
Phases of meiosis II
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Prophase II
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Sister chromatids line up at equatorial plate (metaphase plate)
Anaphase II
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Separation of sister chromatids
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Movement to opposite poles
Telophase II & Cytokinesis
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Nuclear membrane reforms
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Four haploid daughter cells result containing single chromosomes
Spermatogenesis
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Nuclear envelope breaks down and spindles form
Metaphase II
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This is where the reduction in chromosome number occurs from 2N to 1N
Male gamete formation: Result is 4 sperm cells
Oogenesis
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Female gamete formation: Result is 1 ova and 3 polar bodies