If parents have two copies of each chromosome
- Slides: 25
If parents have two copies of each chromosome, how do they pass on only one to their offspring? • MEIOSIS is the process of cell division that decreases the number of chromosomes to make sperm or egg cells Sperm or egg cells Original cell
The purposes of Meiosis: 1. Split the total number of chromosomes in half so that only ONE chromosome from each pair is inherited from each parent. 2. Produce variation in offspring by randomly sorting the chromosomes.
Meiosis Original cell • Diploid (2 n) (n = # of pairs of chromosomes) Sperm or egg cells (GAMETES) • Haploid (n) (single chromosomes)
Fertilization Sperm Egg Gametes: (haploid sex cells) Zygote: (diploid embryo) Fertilized egg
The Cell Cycle – “life” of the cell 4 stages in cell life: G 1 – Growth, making proteins, doing work S – Synthesis – making a copy of DNA G 2 – Growth (more) getting ready for cell division M – Mitosis or Meiosis – cell division
Mitosis • Produces two identical daughter cells • Each daughter cell has the same kind and number of chromosomes as the original parent cell • Mitosis takes place AFTER DNA replication
Interphase (Resting stage) • Chromosomes cannot be seen • Chromosomes duplicate and double in number • How do the chromosomes duplicate?
Prophase nuclear membrane chromatids centromere disappearing • Chromosomes become visible • Each chromosome consists of two identical chromatids homologous chromosomes
Metaphase Centrosome • Chromosomes line up at the equator (centre of the cell) • Spindles are formed to attach to the centromere of each chromosome (made of 2 centrioles)
Anaphase • Sister chromatids separate as individual chromosomes • They move apart towards the opposite poles chromosomes
Telophase • Chromosomes gradually disappear • Nuclear membrane is formed around each set of chromosomes nuclear membrane forming
Can you identify the different stages of mitosis from the diagram below? anaphase interphase telophase metaphase prophase
Meiosis • Same steps as Mitosis: Prophase, Metaphase, Anaphase, Telophase • Meiosis happens TWICE!!! • Metaphase I, Anaphase II, etc. http: //highered. mcgrawhill. com/sites/0072495855/student_view 0/cha pter 28/animation__how_meiosis_works. html
Some Vocab • Homologous Chromosomes: chromosomes that contain the same genes, but may have different alleles (one is from mom, one is from dad) • Sister Chromatids: identical copies of a single chromosome connected by a centromere
Meiosis 1
Close-up of Metaphase I Crossing over: segments of DNA are exchanged between homologous chromosomes
Law of Independent Assortment • It is random where the chromosomes line up! Mom can be either side, Dad either side.
Meiosis II
Close up of Metaphase II
Summary of Meiosis • Segregation of alleles: one chromosome in each of the 4 cells: only one copy of the allele • Creates 4 haploid daughter cells • Meiosis Video
• Comparison of Mitosis and Meiosis
Mitosis vs. Meiosis Mitosis Meiosis Purpose To produce new cells for To produce new 1) growth 2) replacement gametes for sexual of old or damaged cells reproduction Start with 1 Diploid somatic cell 1 Diploid germ cell (i. e. , skin cells, liver cells, muscle cells, lung cells, etc. ) End with 2 identical Diploid somatic cells 4 haploid gametes Number of cell divisions that occur 1 2
• Demonstration of mitosis and meiosis
Mendel’s Laws related to Meiosis • Law of Segregation • Law of Independent Assortment
Pop bead modeling of meiosis • Follow directions from teacher • Use pop beads to model each step in animation with your teacher • Draw each step on your worksheet Meiosis step 1 Meiosis step 2 Meiosis step 3
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