Chapter 9 Cellular Basis of Inheritance

Bell Ringer What happens to your skin cells when you get a cut? Divide and multiply to begin healing. Your skin is actually dead! When a starfish loses a limb, what can the starfish do? Regrow the lost limb.

Why do cells divide? Cells divide to grow and make new cells. Cells divide to replace dead cells. Cells die when they are too old and cannot function any longer. Cells may become damaged. Single cells organisms divide to reproduce.

9.1 All cells come from cells Asexual reproduction: Single cell or group of cells copies its DNA and then splits into two new organisms that are genetically identical Ex. Most unicellular such as Paramecium, but plants as well.

Sexual Reproduction: DNA from two parents combine to produce a genetically different organism. Most multicellular organisms. Egg + sperm = zygote

9.2 The cell cycle multiplies cells Where in the cell are the genes located? Nucleus Cell division: Process by which a cell divides into two new cells.

Chromosome Chromosome: Structures that contain the DNA that is passed from one generation to the next.

Sister “jointed” chromatids: Two identical copies of DNA Centromere: Area where sister chromatids of a chromosome attach.

How many chromosomes? Humans 46 chromosomes 23 pairs Mosquito 6 chromosomes 3 pairs Banana 22 chromosomes 11 pairs

Cell Cycle How often the cell divides depends on the type. Cell cycle: Series of events that cells go through as they grow and divide.

Cell Cycle Interphase: “Prep phase” Copying DNA! The stage during which a cell carries out its metabolic processes and performs its functions. Interphase consists of G1 phase, S phase and G2 phase. G – gap

G1 phase: Phase of intense growth, cells spends most of their time in this phase. S phase (synthesis): DNA is replicated, cell now contains two copies of each chromosome. Forms sister chromatids and centromere.

G2 phase: Continued preparation for cell division. Other organelles are replicated.

Mitotic phase (M phase): Cell cycle when the cell is actually dividing. Includes mitosis and cytokinesis.

Mitosis: The nucleus and the duplicated chromosomes divide and are evenly distributed. Very accurate and unique to eukaryotes. Cytokinesis: Process where cytoplasm is divided into two.

9.3 Cells divide during mitotic phase Spindle fibers: Framework of microtubules that guide the movement of chromosomes.

Mitosis Four main stages. Prophase Metaphase Anaphase Telophase PMAT!

MITOSIS Prophase Chromatin condenses into chromosomes Nuclear envelope breaks down Centrioles separate and spindle fibers begin to form

MITOSIS Metaphase Chromosomes line up across the center “middle” of the cell Each chromosome is connected to a spindle fiber at its centromere

MITOSIS Anaphase Spindle fiber pulls on chromosomes Sister chromatids separate into individual chromosomes at the centromere

MITOSIS Telophase Chromosomes gather at opposite ends of the cell Two new nuclear envelopes form around each new set of chromosomes Chromosomes uncoil Spindle fibers disappear

CYTOKINESIS Cytokinesis – process in which the cytoplasm divides after mitosis RESULT  Formation of two new daughter cells each with an identical set of chromosomes

Cytokinesis Animal Cell vs. Plant Cell Animal cells Form a “cleavage furrow”, where cell pinches in half Plant cells Form a “cell plate,” where a new cell wall and membrane form

Eukaryotic Cell Division

Pneumonic I Play Music And Text Constantly Interphase - G1, S, G2 Prophase Metaphase Anaphase Telophase Cytokinesis Animal cells – cleavage furrow Plant cells – cell plate Mitosis

Cell Cycle

Mitosis Video

Cancer Questions What are some causes of cancer? Smoking Bad diet Chemicals Radiation Alcohol Inheritance

9.4 Cancer cells grow and divide out of control What is a tumor? Abnormal mass of normal cells. Benign or malignant Benign: Usually not harmful Malignant: Problematic can cause severe problems.

What is cancer? Uncontrollable cell division. Disruption telling your cells to stop dividing. Metastasis: Spread of cancer beyond their original site. Tumors usually removed by surgery. Cancer = Radiation therapy or chemotherapy (drugs)

Cancer Cells

9.5 Meiosis functions in sexual reproduction Meiosis: Type of cell division that produces four cells, each with half the number of chromosomes as the parent cell. Mitosis - process by which the nucleus divides to form two nuclei, each containing a complete set of the cell’s chromosomes Meiosis – two-stage form of cellular division that reduces the number of chromosomes per cell by one-half

Karyotype: Display of persons chromosomes Homologous chromosomes: Matching pair of chromosomes from each parent. Sex chromosomes: Determine the persons sex. X Y

Almost all human cells are diploid (2n). They contain two homologous sets of chromosomes. Single set of chromosomes are called haploid (n). Gametes are sex cells (eggs and sperm) and are haploid. For humans n= 23. What is happening in this picture? Sperm (n) is fusing with an egg (n). This is called fertilization. The fertilized egg is called a zygote (2n).

Stages of Meiosis Meiosis 1 Prophase 1: Homologous chromosomes stick together. Form a tetrad. Paired chromosomes consist of four chromosomes. Chromosomes cross over.

Metaphase 1 Tetrads line up in the middle of the cell and line up across the spindle.

Anaphase 1 Homologous chromosomes being to separate to opposite poles.

Telophase 1 and Cytokinesis Chromosomes arrive at pole. Each pole has haploid set of chromosomes. Nucleus reforms and cell divides.

Meiosis 2 Prophase 2: In each haploid daughter cell, spindle forms, attaches to centromeres and more chromosomes.

Metaphase 2 Chromosomes line up in middle of the cell. Spindles attach to each sister chromatid.

Anaphase 2 Sister chromatids separate and move to opposite poles.

Telophase 2 and Cytokinesis Chromosomes arrive at poles. Cytokinesis splits the cells more one time. Produces four haploid daughter cells.

Meiosis I Diploid cell 2N = 4 2 Haploid cells N = 2 Why does crossing-over occur? Crossing-over changes the combination of the genes on chromosomes.  allows for variation among organisms

Meiosis II 2 haploid cells N = 2 4 haploid cells N = 2

Meiosis

9.6 Meiosis increases genetic variation among offspring Crossing over: The exchange of genetic material between homologous chromosomes. Genetic recombination: New combination of genetic information in a gamete resulting in crossing over during prophase 1 of meiosis.

Mitosis vs. Meiosis MITOSISMEIOSIS Why does it happen? Growth, repair, replaceMake sex cells (gametes) Where does it happen in your body? When does it happen during your lifetime? Number of cells formed Number of chromosomes Number of cell divisions Types of cells formed Entire body EXCEPT……….Reproductive organs Fertilization  Death Males Puberty  Death Females Puberty  Menopause 1 cell  4 cells1 cell  2 cells 46  23  23 meiosis I meiosis II 2N  N  N meiosis I meiosis II 46  46 2N  2N OneTwo All EXCEPT…………………Gametes (reproductive cells) Sperm cells Egg cells