Discovering DNA Molymod® miniDNA® Mitosis & Meiosis Instructions and teacher’s guide Cat no MDNA-M&M-432 We’d love to hear any feedback, comments or questions you have! Post: Discovering DNA Ltd, PO Box 280 Hertford, SG13 9DG email: [email protected] tel: 01992 410 140 fax: 01992 410 106 discoveringdna.com Key: Green = Guanine Yellow = Cytosine Dark Blue = Adenine Orange = Thymine Molymod® miniDNA® Mitosis & Meiosis Cat no MDNA-M&M-432 Contents: Blue sugar 72 Cytosine (Yellow) 24 Pink sugar 72 Guanine (Green) 24 Phosphate (Purple) 144 Adenine (Dark Blue) 48 Thymine (Orange) 48 Introduction Fundamental processes Every day an adult human makes many hundreds of millions of cells so cell division remains an essential process throughout our lives. Mitosis and meiosis play separate but mutually important roles. Mitosis is the process of cell division to create two identical daughter cells each with a full complement of chromosomes (diploid). A diploid cell contains two slightly different copies (or homologues) of each chromosome. One is paternal and the other maternal. Meiosis is the form of cell division used to create four daughter cells that will be gametes for sexual reproduction. These cells have half the full number of chromosomes (haploid). After fertilisation between two haploid gametes, the full diploid number of chromosomes is restored. Discovery Mitosis was first discovered by German scientist Walther Flemming in 1878. Meiosis was discovered soon afterwards by Belgian scientist Edouard Van Beneden in 1883. Meiosis drives evolution Meiosis provides variation for evolution through the independent assortment of paternal and maternal chromosomes in the daughter cells and crossing over between maternal and paternal homologous chromosomes during the first meiotic division. Independent assortment creates an enormous amount of variation. As humans have 223 chromosomes, this means there are 8.4 million possible gametes. Crossing over increases this even further as two or three cross overs happen per pair of homologues. This fascinating process is modeled with this set. Meiosis mistakes are common Meiosis often goes wrong and is a major cause of chromosomal abnormalities. For example, non-disjunction is where homologues fail to separate so some gametes have extra or missing chromosomes. This causes Down's Syndrome due to non-disjunction of chromosome 21 during meiosis I. Learning outcomes This set provides enough materials to carry out the lesson with a whole class working as 6 groups. This hands-on activity will help your students remember many key points about mitosis, meiosis and the cell cycle. The set can be used to teach mitosis and meiosis at an introductory level or a more advanced level. By the end of the session, your students will have learnt: • Mitosis • Independent assortment • Meiosis • Homologous recombination • Cell cycle • Crossing over • Terminology Duplication of any part of this document is permitted for classroom use only. This document, or any part, may not be reproduced or distributed for any other purpose without the written consent of the Discovering DNA Ltd. 2 Copyright © 2014 Discovering DNA Ltd, all rights reserved. Key: Green = Guanine Yellow = Cytosine Dark Blue = Adenine Orange = Thymine Time requirements Preparation - The first time will take about 20 minutes but after this preparation is no more than 5 minutes as you can keep the components assembled in the storage box for future use. Lesson - 20 minutes is sufficient to carry out the activity with more time to explain the stages and analyse the outcomes as required. Preparation 1 Assemble chromosome bases You only need to do this once as the bases can be kept for future lessons! Chromosome bases comprise of a sugar (pink or blue), a phosphate (purple) and a base (yellow, green, blue or orange). Please note different sugar colours are included to make it easier to see the paternal or maternal chromosomes they do not represent different chemicals. Use blue sugars for the paternal chromosome and pink sugars for the maternal chromosome. This provides a constant reminder of the origin of the DNA. Attach the purple phosphate to the blue or pink sugar by pushing the bent knob from the sugar into the hole in the purple phosphate. Make sure you add the sugar to the 5’ prime end as shown so the knob still sticks out of the purple phosphate not out of the sugar. Push the coloured base (green, orange, dark blue or yellow) onto the straight knob on the sugar. 5’ prime phosphate 3’ prime sugar base base 5’ prime 3’ prime sugar phosphate Paternal - assemble bases with blue sugars: Maternal - assemble bases with pink sugars: Cytosine (Yellow) x 12 Cytosine (Yellow) x 12 Guanine (Green) x 12 Guanine (Green) x 12 Adenine (Dark Blue) x 24 Adenine (Dark Blue) x 24 Thymine (Orange) x 24 Thymine (Orange) x 24 Helpfully, C, G, A, and T are embossed on the edge of the base. 2 Give out the following bases (enough for 2 chromosomes per group) Group 1 - Chromosome 5 maternal (pink sugars) Cytosine (Yellow) x 4 Guanine (Green) x 4 Adenine (Dark Blue) x 6 Thymine (Orange) x 6 Duplication of any part of this document is permitted for classroom use only. This document, or any part, may not be reproduced or distributed for any other purpose without the written consent of the Discovering DNA Ltd. 3 Copyright © 2014 Discovering DNA Ltd, all rights reserved. Key: Green = Guanine Yellow = Cytosine Dark Blue = Adenine Orange = Thymine Groups 2 - Chromosome 5 paternal (blue sugars) Cytosine (Yellow) x 4 Guanine (Green) x 4 Adenine (Dark Blue) x 6 Thymine (Orange) x 6 Group 3 - Chromosome 6 maternal (pink sugars) Cytosine (Yellow) x 4 Guanine (Green) x 4 Adenine (Dark Blue) x 8 Thymine (Orange) x 8 Group 4 - Chromosome 6 paternal (blue sugars) Cytosine (Yellow) x 4 Guanine (Green) x 4 Adenine (Dark Blue) x 8 Thymine (Orange) x 8 Group 5 - Chromosome 7 maternal (pink sugars) Cytosine (Yellow) x 4 Guanine (Green) x 4 Adenine (Dark Blue) x 10 Thymine (Orange) x 10 Group 6 - Chromosome 7 paternal (blue sugars) Cytosine (Yellow) x 4 Guanine (Green) x 4 Adenine (Dark Blue) x 10 Thymine (Orange) x 10 You can get the students to assemble these (see Teachers Guide for the sequence) or do this in advance of the lesson. After completion of the lesson Separate the bases (with blue and pink sugars) and keep them in the storage boxes for use next time. Keep starting chromosomes intact unless you want your students to make them next time. Preparation for subsequent uses (about 5 minutes) Sort out the bases (with blue and pink sugars) by colour (yellow, green, dark blue or orange). Give out starting chromosomes. Then you are ready to go! Duplication of any part of this document is permitted for classroom use only. This document, or any part, may not be reproduced or distributed for any other purpose without the written consent of the Discovering DNA Ltd. 4 Copyright © 2014 Discovering DNA Ltd, all rights reserved. Key: Green = Guanine Yellow = Cytosine Dark Blue = Adenine Orange = Thymine Mitosis & Meiosis – Teacher’s Notes Lesson tips Important - ensure students have bases correctly orientated so 5’ and 3’ are opposite each other when bases are paired (shown on page 4) & don’t let your students take the bases or chromosomes apart! Remember in base pairing the following match: T pairs with A (orange with dark blue) C pairs with G (yellow with green) Lesson plan • Each group of students makes one double stranded chromosome (maternal or paternal) • Each group carries out mitosis • Each group carries out meiosis We make six chromosomes - a maternal and paternal homologue of each of three different chromosomes numbered 5, 6 and 7. Using DNA strands reinforces the idea that chromosomes are long strands of DNA. Real human chromosomes are millions of base pairs in length so we have scaled it down for this activity. Student groups work with either a maternal (pink sugar) or paternal (blue sugar) homologue of one chromosome. Whilst focus on chromosomes we give details of each stage of mitosis, meiosis and the cell cycle for clarity. These are omitted from the student guide so you can cover as much or as little as you want. We also show all the chromosomes in the photos but each group works with just one of the homologues. Lesson Part One – Mitosis Mitosis makes exact copies of cells for growth and repair. Mitosis starts with a diploid cell and produces two identical daughter cells. Each daughter cell contains two copies of every chromosome - maternal and paternal. These are called homologous chromosomes (or homologues). They are similar (same size, position of centromere, same genes present at same loci) but not identical in DNA sequence. The variation in maternal and paternal chromosomes is one of the things that make us all different. 1 Each group makes one chromosome - either maternal or paternal. Chromosome numbered after number of bases in them (chromosome 5 have 5 bases and so on). The sequences are slightly different between the maternal and paternal homologues. Group 1 makes maternal chromosome 5 (pink) - 5 bases long: 5'-AGGTA-3' 3'-TCCAT-5' Group 2 makes paternal chromosome 5 (blue) - 5 bases long: 5'-AGGAA-3' 3'-ACCAA-5' Duplication of any part of this document is permitted for classroom use only. This document, or any part, may not be reproduced or distributed for any other purpose without the written consent of the Discovering DNA Ltd. 5 Copyright © 2014 Discovering DNA Ltd, all rights reserved. Key: Green = Guanine Yellow = Cytosine Dark Blue = Adenine Orange = Thymine Group 3 makes maternal chromosome 6 (pink) - 6 bases long: 5'-TGGAAT-3' 3'-ACCTTA-5' Group 4 makes paternal chromosome 6 (blue) - 6 bases long: 5'-AGGAAA-3' 3'-TCCTTT-5' Group 5 makes maternal chromosome 7 (pink) - 7 bases long: 5'-AGGATAA-3' 3'-TCCTATT-5' Group 6 makes paternal chromosome 7 (blue) - 7 bases long: 5'-AGGTTAA-3' 3'-TCCAATT-5' 2 Once each group has made a chromosome, as a class, look at the chromosomes before mitosis begins.