Biology Chapter 10 Cell Reproduction I. Chromosomes Long thin molecules that store genetic information. A. Chromosome Structure 1. Rod shaped structure composed of DNA and protein. 2. DNA is wrapped around molecules of protein called histones a. maintains shape b. aids in tight packing CHROMOSOME STRUCTURE 1
3. The coils are further packed together into super coils SUPERCOILS 4. During cell division the DNA uncoils and is copied The DNA and its copy join and are called chromatids. They are attached at the center by a centromere 2
5. Prokaryotes usually have only one chromosome attached to the inside of the cell membrane. B. Chromosome Numbers The complexity of organisms is not determined by the number of chromosomes they have. 1. Sex chromosomes and autosomes. a. Sex chromosomes determine the sex of an organism. Different species have different chromosome mechanisms that serve this function. b. Humans have 2 sex chromosomes X and Y XX is female XY is male 3
OTHER SYSTEMS c. Autosomes All chromosomes except the sex chromosomes are called autosomes. Humans have 44 autosomes arranged in 22 pairs. The pairs are formed from similar chromosomes inherited from each parent. The chromosomes that make a pair are called homologous chromosomes c. A karyotope is a chart of the chromosomes that are contained in the cells of an organism. Human Karyotype 4
2. Diploid and Haploid cells a. Diploid cellscontain both chromosomes for each homologous pair, including both sex chromosomes. Diploid cells are abbreviated 2n b. Haploid cells Contain only one chromosome from each homologous pair. Gametes are haploid cells. Haploid cells are abbreviated n 2 haploid cells combine to Form a diploid cell in sexual reproduction. n + n 2n II. Cell Division Process by which cells produce offspring cells. A. Cell division in prokaryotes 1. Binary fission cell divides into two identical daughter cells. 5
CELL DIVISION Steps of Binary Fission Parent cell grows to its maximum size. In prokaryotes (bacteria and Archaea), a new cell wall, called a septum, begins to grow across the middle of the cell, bisecting it. Amoeba, which do not have a cell wall, develop a cleavage furrow that pinches the cell in half. Yes- this is still under binary fission Cell duplicates its chromosome (a process called replication) so that two exact copies of the genetic material exist inside the parent cell. These two molecules of DNA are attached to the cell s plasma membrane. The cell then grows, increasing the distance between the two duplicated chromosomes that are attached to the plasma membrane. Yup more binary fission independent unit. After the septum forms completely, depending on the type of microbe, the daughter cells may remain attached to each other, or may completely separate. Whether attached or separated, each cell is an 6
This process repeats, sometimes very quickly, such as in E. coli bacteria which divides every 15 minutes, or very slowly, such as in Mycobacteria leprae, the causative agent of leprosy, which only divides once every two weeks. B. Cell Division in Eukaryotes Mitosis results in new cells with genetic material identical to the original cell. Meiosis results in new cells with ½ the genetic material of the original cell. MITOSIS VS MEIOSIS 7
1. The cell cycle Repeating set of events that makes up the life of the cell. a. Stages 1. Interphasetime between cell divisions. 2. Mitosis (M-phase) nucleus divides. 3. Cytokinesis cytoplasm divides. EUKARYOTIC CELL CYCLE a. Interphase Most of the life of the cell Stages 1. G 1 Phase Normal growth and development of the cell. 2. S Phase The cell s DNA is copied 3. G 2 Phase Organelles are copied and the cell prepares to divide. 8
INTERPHASE b. MITOSIS 1. Prophase i. DNA shortens into visible chromatids. ii. The nucleus and the nucleolus disappear. iii. 2 pairs of centrosomes appear and move to opposite poles. (animal cells contain centrioles) iv. The mitotic spindle composed of spindle fibers radiate from the centrosomes. v. Kinetochore fibers attach to the centromeres of the chromatids. vi. Polar fibers extend from centrosome to centrosome. PROPHASE 9
PROPHASE 2. Metaphase The kinetochore fibers move the chromosomes to the center of the cell. METAPHASE 10
CHROMOSOME SEPARATION METAPHASE 3. Anaphase The chromatids of each chromosome separate and are pulled to opposite poles of the cell. 11
ANAPHASE ANAPHASE 4. Telophase 1. The chromosomes return to a less coiled state. 2. The spindle fibers break down. 3. A nuclear envelope forms around each set of chromosomes. 4. The nucleolus forms. 12
TELOPHASE TELOPHASE AND CYTOKINESIS PLANT MITOSIS 13
INTERPHASE PROPHASE METAPHASE 14
ANAPHASE TELOPHASE MITOSIS 15
MITOSIS CYTOKINESIS CYTOKINESIS IN ANIMALS 16
MITOSIS ANIMATION C. Meiosis Production of gametes by reducing the chromosome number from 2n to n 1. Stages of Meiosis a. Meiosis I 1. Prophase 1 a. Chromatin coils tightly into chromatids. b. Each chromatid lines up next to its homologue. synapsis (this does not occur in mitosis) c. Each set of homologous chromatids is called a tetrad 17
d. Crossing Over - sometimes occurs at this point Exchange of genetic material between chromadids. This results in genetic recombination A new mixture of genetic material. SYNAPSIS 2. Metaphase 1 a. Tetrads line up along the equator of the cell in a random manner. b. Spindle fibers attach to the centromeres. 18
3. Anaphase 1 a. Independent Assortment occurs at this point. The homologous chromosomes are randomly pulled to opposite poles of the cell 4. Telophase 1 a. Chromatids are at opposite poles of the cell. b. Cytokinesis forms 2 new cells. The nuclear membrane may or may not form at this time. b. Meiosis II 1. Prophase II Spindle fibers form moving the chromosomes in the 2 new cells to the middle of the cell. 19
2. Metaphase II 3. Anaphase II 4. Telophase II The 4 cells produced have ½ the number of chromosomes of the original cell. 20
Review 2. Formation of Gametes a. Spermatogenesis One diploid cell undergoes meiosis and produces four haploid cells called spermatids. The spermatids develop into mature sperm cells. GAMETE FORMATION 21
b. Oogenesis One diploid cell undergoes meiosis and unequal cytokinesis to produce one egg cell and three smaller cells called polar bodies which degenerate. 3. Asexual and sexual reproduction a. Asexual Reproduction 1. Production of offspring from one parent. 2. Offspring are genetically identical to the parent. 3. Binary fission, budding, etc. b. Sexual reproduction 1. Production of offspring from two parents. 2. Offspring are genetically different from the parents. 3. Creates variation in a population. 22
MEIOSIS DNE EHT 23