Presentation on theme: " Rod shaped structures inside the nucleus of Eukaryotic cells Made of DNA and proteins Contain the genes that make you, you! Shape of the chromosome."— Presentation transcript:
3 forms of a chromosome › Chromatin – ball of yarn › Chromatid – half of an x, sometimes bent › Chromosome – X Center of X is called a centromere
Sex Chromosomes › Determine the sex of the organism › Males XY › Females XX › 2 out of 46 in the human cell Autosomes › All the other chromosomes › 44 out of 46 in the human cell
Chapter 8 Click below to watch the Visual Concept. Visual Concept Sex Chromosomes and Autosomes Section 1 Chromosomes
Also called homologues 2 copies of the chromosome › One from Mom; One from Dad Have the same size Have the same shape Have the same information (genes)
Diploid › Cells that have chromosomes in pairs › Symbol 2n › Somatic cells or body cells are like this › Humans diploid number is 46. Haploid › Cells that do not have chromosomes in pairs › Symbol 1n › Gametes are like this Sex cells Sperm and egg cells › Humans haploid number is 23.
Section 2 Cell Division Chapter 8 Cell Division in Prokaryotes, continued Binary fission is the process of cell division in prokaryotes.
Mitosis begins (cell begins to divide) Chromosomes are visible Centrioles (or poles) appear and begin to move to opposite end of the cell. Spindle fibers form between the poles. Centrioles Sister chromatids Spindle fibers Nuclear membrane & nucleolus disappear by end of prophase
Two new nuclei form. Chromosomes appear as chromatin (threads rather than rods). Mitosis ends. Nuclei Chromatin Nuclear membrane & nucleolus are visible by end of telophase Overlaps with cytokinesis!
Division of the cytoplasm Cell membrane moves inward to create two daughter cells – each with its own nucleus with identical chromosomes. Animal cells – form a cleavage furrow Plant cells – form a cell plate, which becomes the cell wall.
Section 2 Cell Division Chapter 8 Control of Cell Division Cell division in eukaryotes is controlled by many proteins. Control occurs at three main checkpoints. 1.G1 checkpoint – check to see whether the cell is healthy and is large enough to divide 2.G2 checkpoint – check to make sure DNA is copied correctly 3.Mitosis checkpoint – if cell divided correctly, then signals are made to exit mitosis
Chapter 8 Click below to watch the Visual Concept. Visual Concept Control of the Cell Cycle Section 2 Cell Division
Chapter 8 Control of Cell Division, continued When Control is Lost: Cancer –Cancer is uncontrolled growth of cells –Cancer may result if cells do not respond to control mechanisms. –Can be caused by mutations in DNA
Section 3 Meiosis Chapter 8 Formation of Haploid Cells Meiosis is a process of nuclear division that reduces the number of chromosomes in new cells to half the number in the original cell. Start with 46 and end with 23 Meiosis leads to four haploid cells (gametes) rather than two diploid cells as in mitosis. Done by germ cells Meiosis produces haploid gametes. Is considered sexual reproduction Creates genetic diversity Two divisions
Section 3 Meiosis Chapter 8 Meiosis I Meiosis I includes prophase I, metaphase I, anaphase I, and telophase I. Crossing-over, which is when portions of homologous chromosomes exchange genetics material, occurs during prophase I and results in genetic recombination.
Homologous chromosomes (paired chromosomes) become visible Nuclear membrane and nucleolus disappear Spindle fiber starts to appear Crossing over occurs – portions of the chromatid break off and attach to other homologous chromosome
Chapter 8 Click below to watch the Visual Concept. Visual Concept Tetrads and Crossing-over of Genetic Material Section 3 Meiosis
Homologous chromosomes (tetrads) line up at the equator and connect to spindle fibers at their centromeres
Homologous chromosomes split and individual chromosomes move to poles They assort independently of one another- independent assortment
There are 2 new cells at this point Each new cell has half the number of chromosomes as the parent germ cell So they are now haploid
Has prophase II, metaphase II, anaphase II and telophase II Exactly like mitosis Four new haploid cells result › Four gametes › Depends on whether it is an animal or a plant cell
Spermatogenesis › Making of sperm cells › Meiosis will result in 4 mature sperm cells or spermatozoa Oogenesis › Making of mature egg cells, or ova › Meiosis will result in 1 mature egg cell and 3 polar bodies that die