Interphase This cell is shown, as this is how all cells look before mitosis. Please be aware that Interphase is a phase of the cell cycle, but NOT a stage of mitosis.
Mitosis - Early Prophase To begin mitosis, the nuclear membrane breaks down, while the chromosomes shorten and thicken (here, a chromosome is two chromatids, bound at a point called the centromere, making an "X" shape). The other structures important for mitosis are also forming (i.e. the centrioles).
Mitosis - Metaphase The spindle has now formed and the nuclear membrane has broken down. The chromosomes are lined up along the cell's center and are attached to the spindle fibers. When the individual chromatids (½ of the "X") are separated from the chromosome (the "X"), they are now each referred to as a chromosome (i.e. In metaphase, the chromosome, composed of two chromatids, separates into the individual chromatids, which are then renamed chromosomes).
Mitosis - Anaphase The newly formed chromosomes are pulled along the spindle toward opposite poles of the cell.
Mitosis - Telophase The chromosomes have finished their migration to the poles. The spindle has broken down and disappeared. The cell membrane pinches in (forms a cleavage furrow) along the center creating two separate cells. At this time, the chromosomes uncoil and become less visible (as they are during Interphase), the nuclear membrane reforms. The division of the cytoplasm is called cytokinesis. The division of the nucleus is Mitosis. At the end of Telophase, the cell reenters Interphase.
Now that we have reviewed the steps of mitosis lets complete a gallery walk to name the stages of mitosis.
Watch the following video and answer the questions below. https://www.youtube.com/watch?v=JcZQkmooyPk 1.About how many cells does an adult human have? 2.How many cells do we start off as? 3.How do we go from so little to so many? 4.What is the process that allows for cells to grow, develop and repair in Eukaryotic cells? 5.Why do daughter cells have the same genetic makeup as the parent cell? 6.When do all of the cells organelles and centrioles replicate? 7.What occurs during the S phase, synthesis phase, of interphase? 8.When do all of the enzymes needed to aid in the process of cell division produced? 9.Do cells spend more time in interphase or in the division phase? 10.What type of cells contain centrioles? 11.What is the difference between animal and plant cells in cytokinesis? 12.What is the purpose of checkpoints in cell cycle? 13.On average what is the length of cell cycle? 14.What is the purpose of mitosis? 15.Predict what would happen to a human if mitosis suddenly stopped.
Vocabulary Haploid: cells that have one set of chromosomes. Diploid: cells that contain two sets of chromosomes one from each parent. Sperm: male gamete (haploid) Egg: Female gamete (haploid) Zygote: diploid cell formed after fertilization. Somatic cell: all body cells except sperm or egg. These cells are diploid. Gamete: sex cells such as a sperm or egg. These cells are haploid. Meiosis: The process that produces haploid sex cells.
Sexual Reproduction During sexual reproduction two gametes from two different organisms of the same species come together. – This process is called fertilization – The cells that forms is called a zygote. Once the zygote is formed the cell then goes through cell cycle (IPMATC) in order for the cell to grow and develop.
Purpose of meiosis Turn diploid cells into haploid cells and to make sure the offspring has the same diploid number as its parent. What would happen in sexual reproduction if two diploid cell combined?
What’s the difference? Diploid Cells – Cells have pairs of similar chromosomes – Somatic cells (body cells) – In humans-46 chromosomes =23 pairs. Each chromosome has a mate that is similar to it in size, shape and DNA. Haploid Cells – Means single form – Do not have pairs – Half the # of chromosomes as somatic cells – Gametes (sex cells) – Human gametes have 23 chromosomes
How are gametes made? Through a process called meiosis. How are somatic cells made? Once a cell has been fertilized somatic cells are made through a process called mitosis. Somatic cell Gamete
Meiosis Occurs before sexual reproduction. Creates gametes (sperm (male) and egg (female)) 2 divisions of the nucleus – Meiosis I – Meiosis II
Meiosis I Before meiosis begins, each chromosome is duplicated, just as in mitosis.
Meiosis I When the cell is ready for meiosis, each duplicated chromosome is visible under the microscope as two chromatids.
Meiosis I The events of prophase I are similar to those of prophase in mitosis. In meiosis, each duplicated chromosome comes near its similar duplicated mate. In mitosis they do not some near each other.
Meiosis I In metaphase I, the pairs of duplicated chromosomes line up in the center of the cell. The centromere of each chromatid pair becomes attached to one spindle fiber, so the chromatids do not separate in anaphase I.
Meiosis I In anaphase I, the two pairs of chromatids of each similar pair move away from each other to opposite ends of the cell. Each duplicated chromosome still has two chromatids.
Meiosis I In telophase I, the cytoplasm divides, and two new cells form. Each new cell has one duplicated chromosome from each similar pair.
Meiosis II The two cells formed during meiosis I now begin meiosis II.
Meiosis II The chromatids of each duplicated chromosome will be separated during this division.
Meiosis II In prophase II, the duplicated chromosomes and spindle fibers reappear in each new cell.
Meiosis II In metaphase II, the duplicated chromosomes move to the center of the cell. Unlike what occurs in metaphase I, each centromere now attaches to two spindle fibers instead of one.
Meiosis II The centromere divides during anaphase II, and the chromatids separate and move to opposite ends of the cell. Each chromatid now is an individual chromosome.
Meiosis II As telophase II begins, the spindle fibers disappear, and a nuclear membrane forms around the chromosomes at each end of the cell. When meiosis II is finished, the cytoplasm divides.
Summary of Meiosis Remember that meiosis produces haploid sex cells. Click box to view movie. This animation will help you further understand meiosis.
Mistakes of Meiosis Meiosis occurs many times in reproductive organs. Mistakes can produce sex cells with too many or too few chromosomes.
Mistakes of Meiosis Sometimes, zygotes produced from these sex cells die. If the zygote lives, every cell in the organism that grows from that zygote usually will have the wrong number of chromosomes. Organisms with the wrong number of chromosomes may not grow normally.
Section Check Question 1 Answer _______ is the joining of an egg and a sperm. The answer is fertilization. Fertilization occurs during sexual reproduction.
Section Check Question 2 _______ and _______ are the two types of cells your body forms. A. body and sex B. egg and sperm C. meiosis and mitosis D. zygote and embryo
Section Check Answer The answer is A. Egg cells and sperm cells are both types of sex cells.
Section Check Question 3 Which best describes the sperm and egg?
Section Check A. typical body cells B. haploid cells C. zygotes D. diploid cells
Section Check Answer The answer is B. Sperm and eggs are sex cells that do not have pairs of chromosomes.