Mitosis and Meiosis aka Cell Division Cell Reproduction Mitosis and Meiosis aka Cell Division

Mitosis New cells are produced by the process of cell division, the dividing of a cell into new cells. Also, in cell division, both nucleus and cytoplasm divide.

Mitosis Vocabulary What is a homologous chromosome? Refers to pairs of like chromosomes What is diploid? The total number of chromosomes What is haploid? Half the total of diploid chromosomes

Mitosis Vocabulary… What does “2n” represent? This is the symbol for the diploid number. “n” is equal to the number of pairs of chromosomes How many chromosomes in humans? 46 – this is the “2n” number. “n” = ?

Mitosis Vocabulary… What is a parent cell? Refers to the cell that will go through cell division What are daughter cells? Cells that are formed in cell division – the result of cell reproduction

Chromosomes What are chromosomes? Carrier of genetic materials, thread-like fibers found in the nucleus What happens to the chromosomes during cell division? During cell division, the chromosomes are passed to the new cells that are formed They are composed of genes

Chromosomes… What are sister chromatids? two distinct strands that make up chromosomes What is a centromere? Structure that holds the chromatids together

Chromosomes… What are genes? Made up of DNA and are units of heredity; unique to everyone What are traits? Are physical and unseen characteristics. Examples: physical: color of skin or eyes unseen: blood type or intelligence level

Chromosomes… What are living things made of? Made of cells that contain a certain number of chromosomes. Examples: body cells of an onion plant contains 16 chromosomes How many chromosomes does a human have? 46 chromosomes

What is mitosis? Type of cell division by which chromosomes double to form two complete identical cells or daughter cells Each daughter cell receives the same number of chromosomes that the parent cell had

Why do cells divide? Cell size is an important factor in causing a cell to divide A cell will not continue to grow indefinitely, when a cell reaches a certain size, it will divide

The Cell Cycle Consists of 3 stages: Interphase Mitosis Cytokinesis

What is interphase? First stage of the cell cycle “resting” stage is the period in which cells carry out many activities other than mitosis Interphase is not a part or period of mitosis; this phase precedes mitosis and follows cytokinesis

Stages of interphase G1 Phase – the cell doubles in size, enzymes and organelles, such as mitochondria and ribosomes, roughly double in number S Phase – the DNA that makes up the chromatin replicates – chromosomes double. Example: human chromosomes go from 46 chromosomes to 92 chromosomes G2 Phase – the cell undergoes rapid growth that prepares it for mitosis, makes the necessary enzymes and structures

Second stage of the cell cycle Stages of mitosis Prophase Metaphase Anaphase Telophase Second stage of the cell cycle

What happens during prophase? Chromosomes come in pairs, appear shorter and thickened Nuclear membrane and nucleolus disintegrate or disappear Centrioles move to the opposite ends of the cell Spindle fibers form at the centrioles

What happens during metaphase? Paired thick chromatids move to the center or equator of the cell and line up along the equator The centromere of each pair of chromatid is attached to a spindle fiber from the centriole

What happens during anaphase? Centromeres split and the spindle fibers pull the sister chromatids apart The paired chromatids are now individual chromosomes Separated chromosomes are moved towards the opposite poles of the cells or to the ends of the spindle fibers

What happens during telophase? In animal cells, cytoplasm pinches together along the equator until two daughter cells are formed In plant cells, a cell plate forms between the 2 new cells Chromosomes become thread-like by uncoiling Nuclear membrane and nucleolus reform Spindle fibers begin to breakdown

What is cytokinesis? Third stage of the cell cycle The division of the cytoplasm Produces 2 new daughter cells

Animal or plant division Animal cells: The cell pinches in on both sides to form a cleavage furrow. Plant cell: The cell forms a cell plate between to 2 new cells.

What does mitosis accomplish? Reproduction of cells Equal distribution of DNA (genetic information) to each daughter cell http://www.johnkyrk.com/mitosis.html

Example of mitosis Fruit Fly has 8 diploid chromosomes Mitosis = parent cell division into 2 daughter cells Fruit fly – how many chromosomes at each phase? Interphase – (still one cell) Prophase - (still one cell) Metaphase - (still one cell) Anaphase - (still one cell) Telophase – (two new cells)

Normal cells Animal Cells/Diploid Humans – 46 Cat – 38 Cow – 60 Dog – 78 Fruit Fly – 8 Goldfish – 94 Grasshopper – 14 Housefly - 12 Plant cells/Diploid Onion – 16 Pea – 14 Apple – 34 Sunflower – 34 Plum – 48 Rice – 12 Tobacco – 48

Normal cells… Notice that the numbers for all organisms listed are even numbers. Chromosomes in the body cells of all organisms occur in pairs. Homologous chromosomes – refers to pairs of like chromosomes Example: In cat cells there are 19 pairs of chromosomes

What is cancer? Uncontrolled cell division The cell never goes into interphase Always in a state of division

What factors contribute to the development of cancer? Genetic malfunction where enzymes that start and stop the cell cycle are either not produced or are over produced When cells no longer respond to the chemicals that are secreted to prevent the overcrowding of cells. This is known as contact inhibition Environmental factors: cigarette smoke, air and water pollution, and exposure to ultraviolet radiation

What are the steps of cancer? Genes controlling enzyme production are disrupted Changes occur in the cell cycle for cell reproduction Environmental factors trigger the cancer cell to grow Cancer cells crowd normal cells preventing nutrients form getting to the normal cells A tumor forms Cancer cells break away from original cancer growth Cancer cells enter circulatory system and spread throughout the body New tumors form disrupting normal organ function

Practice quiz What is the diploid number for human chromosomes? 46 What holds sister chromatids together? Centromere What are the stages of the cell cycle? Interphase, mitosis, cytokinesis

Practice quiz… What are the stages of mitosis? (in order) Prophase, metaphase, anaphase, telophase In what phase does the DNA double? Interphase In what phase do the chromosomes line up in the center of the cell? metaphase

Meiosis Cell division where one diploid cell (2n) produces four haploid (n) cells called sex cells or gametes These cells have half the number of chromosomes as a body cell of a parent

Meiosis vocabulary What is a gamete? Male and female sex cells; the sperm and egg What is the male gamete? Sperm; has 23 chromosomes What is the female gamete? Egg; has 23 chromosomes

Meiosis vocabulary… What is a zygote? A fertilized egg – has a diploid number (2n) of chromosomes What is sexual reproduction? The pattern of reproduction that involves the production and fusion of haploid sex cells What is a diploid cell? Cell containing two of each kind of chromosome from the parent

Meiosis vocabulary… What is a haploid cell? Cell containing one of each kind of chromosome from the parent What is an allele? Gene form for each variation of a trait of an organism. Example: gene for height can express tall or short Homologous chromosomes: Pairs of like chromosomes even though the alleles may be different – so they are not identical chromosomes – sibling variation

The Phases of Meiosis Meiosis I Interphase Prophase I Metaphase I Anaphase I Telophase I Meiosis II Prophase II Metaphase II Anaphase II Telophase II

Interphase Carries out metabolic activities of the cell Replicates its chromosomes Precedes meiosis 1

Prophase I Chromosomes coil up and spindle form Homologous chromosomes pair up and a four-part structure called a tetrad forms

During prophase I… Tightly wound tetrads get so close to one another that the genetic material from one homologous pair exchanges with the other creating new combinations of alleles in the genetic code Nuclear membrane disappears Nucleolus disappears

What is crossing over? Exchange of genetic material by non-sister chromatids during prophase I Results in new combinations of alleles

Metaphase I Tetrads line up at the equator Homologous chromosomes are lined up in pairs along the midline or equator of the cell Spindle fibers attach to the centromere on each pair The pairs are not attached to each other

Anaphase I Homologous chromosomes are separated and pulled to opposite poles of the cell The centromeres do not split during this phase Each new cell receives only one chromosome from each homologous pair

Telophase I Spindle breaks down Chromosomes uncoil Cytoplasm divided in 2 Each cell has half the genetic information from the original cell Chromosomes are still doubled containing two sister chromatid Nuclear membrane reforms Two diploid daughter cells formed

Meiosis II Is there an interphase in Meiosis II? No. Chromosomes do not replicate The cells go directly from meiosis I to meiosis II

Prophase II Spindle forms in each of the two new cells Chromosomes are still coiled as sister chromatids Nuclear membrane disappears Nucleolus disappears

Metaphase II Chromosomes line up at the equator of the cell Spindle fibers attach to the centromeres

Anaphase II Centromeres split Spindle fibers pull separated chromatids to opposite poles of the cell

Telophase II Spindle fibers disappear Chromosomes uncoil Nuclear membrane reforms Nucleolus reforms Cytoplasm divides Each cell now has half the chromosomes that its parents had Four daughter haploid cells are formed

What are the two divisions of meiosis? Meiosis I and Meiosis II Meiosis I When homologous chromosomes come together and separate Meiosis II The division that results in 4 daughter cells, each with half the chromosomes present in the original cell

What is genetic recombination? Genetic variation due to crossing over and random assortment How many ways can the chromosomes line up? 2

How do you find the total number of different kinds of sperm and egg that can be produced? Take the number of pairs and place it as the exponent with a base of 2 Example: in humans there are 23 pairs of chromosomes For sperm: 223 = over 8 billion For egg: 223 = over 8 billion

What is the total when fertilization occurs? 223 * 223 = 70 trillion zygotes are possible

What is oogenesis? Refers to the formation of the egg cell

What is spermatogenesis? Refers to the formation of the sperm cell