Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Mitosis and Meiosis Chromosomes • Chromosomes are made up of DNA which carries the cells genetic information • Human body cells have 46 chromosomes (in 23 pairs) • Sex cells (gametes aka egg and sperm) only have 23 chromosomes • Before cell division occurs, each chromosome replicates (or copies itself) Sister Chromatids Centromere Cell Growth and Division Cell Cycle is a series of events that cells go through as they grow, prepare for division and divide into two identical daughter cells Two major stages in a cells life are: 1. Interphase 2. M Phase or cell division Interphase Interphase is the phase where the cell grows and prepares to divide. Interphase is divided into three phases: • G1 Phase - growth • S Phase – replication (copying) chromosomes • G2 Phase – further growth * A lot is happening during G1, S and G2 phases! M Phase M Phase is cell division which includes two steps: 1. Mitosis- this is division of the nucleus 2. Cytokinesis – this is division of the cytoplasm Mitosis Mitosis is divided into four phases: 1. Prophase – chromosomes condense, becoming visible; centrioles move to opposite sides of nucleus; nuclear envelope dissolves 2. Metaphase – chromosomes line up across middle of cell 3. Anaphase – sister chromatids split 4. Telophase - sister chromatids move to opposite sides of cell and new nuclear envelopes form Cytokinesis • Cytokinesis is occurring at the same time as telophase • The cell membrane pinches the cytoplasm into two equal parts. • Two new daughter cells are now formed and are genetically identical to the parent cell. • This is the end of the cell cycle. MEIOSIS Meiosis is process where the number of chromosomes per cell is divided in half by separating homologous chromosomes in a diploid cell. Gametes are produced by meiosis. What does all that mean??? • Chromosomes are made up of DNA which carries the cells genetic information • Genes are found on the chromosomes. • Genes are chemical factors that determine traits. (Ex. Eye color, hair color, height, etc.) • Different forms of a gene are called alleles (Ex. Blue or brown eyes, brunette or auburn) N * The symbol represents the number of chromosomes in a gamete (sex cell) Homologous chromosome means that each chromosome that comes from the male has a corresponding chromosome from the female Homologous chromosome have DNA segments, or genes, for the same trait • Diploid cells have both sets of homologous chromosomes (one set from momma and one from the baby’s daddy) – All cells in your body (except egg and sperm) are diploid – These cells are called somatic cells – 2N • Haploid cells have half the number of chromosomes as their parent cells • Gametes (egg and sperm) are haploid • Gametes are genetically different than the parent cell and one another • N N N N 2N N N N Human has 46 chromosomes. How many chromosomes in human gametes? 23 Pineapple has 25 chromosomes in its gametes. What is it’s haploid number? 25 A giraffe has a diploid number of 62. What is it’s haploid number? 31 Draw this! 46 First Step Replication • During meiosis, chromosomes are replicated once in S phase (just like mitosis) into sister chromatids. • This occurs so that each of the 46 chromosomes exists as a duplicated sister chromatid. Meiosis I • HOMOLOGUES (1-23) are segregated into different cells. • Results in 2 cells that each have 1 copy of each of the 23 chromosomes (still duplicated from DNA replication). Prophase I Crossing over • Homologous chromosomes in the cell pair up alongside each other lengthwise forming a tetrad • Swap bits and pieces of their chromosomes, shuffling the genome • Results in NEW Chromosomes that did not exist before in the parent Meiosis II • SISTER CHROMATIDS of each of the 23 chromosomes are pulled apart just as they are in mitosis • Results in 4 cells that have 1 copy of each of the 23 chromosomes (now unduplicated again) • Now officially haploid Meiosis occurs in two stages Meiosis I • Two cells form with sets of chromosomes and alleles that are different from each other Meiosis II • Cells divide again without DNA replication forming four cells with half the number of chromosomes of the parent cell Summary of Mitosis/Meiosis Mitosis • Results in 2 identical cells that are diploid (2N) and are exactly like the parent cell Meiosis • Results in 4 cells that have half the number of chromosomes, haploid (N), as the parent cell and are genetically different from one another • Genetic Recombination Meiosis Square Dance Linked Genes - Genes located closely together are linked Crossing over is more likely to occur between genes that are far apart rather than linked which are close together. Polyploidy – The occurrence of one or more extra chromosomes in an organism. This is not good in animals but is beneficial in plants (crop plants are stronger and bigger)