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BEDE BUGS INTRODUCTION This activity demonstrates the principles of “Independent assortment of chromosomes” and shows how meiosis leads to tremendous genetic variation. illustrates how independent assortment of chromosomes and random fertilisation of haploid gametes produced by meiosis lead to genetic variation Bede Bugs are creatures that live in the College Social Area, feeding on the dead skin of students. They are shy creatures, – they only come out at night – so you’re very lucky to see one. But most importantly, Bede Bugs are excellent subjects for genetic study, because they have some very distinctive features. IMPORTANT INFORMATION! Bede Bugs have 7 pairs of homologous chromosomes – these are represented by 7 pairs of different coloured card. The sex chromosomes X and Y are represented by white card. We are going to follow the inheritance of 7 different features (phenotypes), carried on 7 different pairs of chromosomes. Bede Bugs have 2 copies (alleles) of each gene, carried on different pairs of chromosomes. E.G. A Bede Bug of genotype Aa carries allele A on one (orange) chromosome and allele a on its homologous chromosome (orange) See Table 2 for possible phenotypes & genotypes of a Bede Bug. To check you understand this table, fill in the phenotypes of the parent Bede Bugs in Table 1. Table 1 Bede Bug Parents Aa Bb Dd Gg Hh Qq Chromosome Colour Orange Blue Pink Green Yellow Purple XY XX White White Genotype Phenotype NOTE! EVERYONE WILL BE STARTING WITH PARENTS OF EXACTLY THE SAME GENOTYPE – THE ONLY DIFFERENCE BEING THAT SOME OF YOU WILL HAVE MALE BEDE BUGS AND SOME WILL HAVE FEMALES Table 2 Your Baby Bede Bug YOUR BABY BEDE BUG Feature Phenotype (Appearance) Antennae Orange Antennae Blue Antennae Number of Three Eyes Eyes Two Eyes One Eye Colour of Legs Pink legs Purple legs Colour of Body Green body Yellow body Colour of Tail Golden Tail Red Tail Shape of Tail Curly Tail Straight Tail Sex Genotype (Genetic makeup) AA or Aa aa BB Bb bb DD or Dd dd GG or Gg gg HH or Hh hh QQ or Qq qq Male (White Nose) Female (Pink Nose) Chromosome Colour Genotype Phenotype Orange Blue Pink Green Yellow Purple XY White XX White Figure 1 Creating your Baby Bede Bug Antenna (small bent pipe cleaner: orange or blue) Eyes (drawing pins: 1,2 or 3) Tail large pipe cleaner: gold or red; straight or curly) Nose (marsh mallow on cocktail stick: pink or white) Legs (cotton buds: pink or purple) Body (pan scourer: yellow or green) MEIOSIS SIMULATION 1. On your own, place your cards face down and shuffle them about. These cards represent your parent Bede Bug’s chromosomes (diploid number). 2. Leave the cards face down and put them into homologous (coloured) pairs. Chromosomes actually do pair up like this during Prophase I of meiosis. 3. Pick one card –any card- from each pair This simulates independent assortment of the chromosomes during Metaphase II, where the arrangement of the chromosomes above and below the spindle fibre equator occurs at random. 4. You should now have 7 cards, one of each colour. This set of cards represents your gamete (egg or sperm), which has half the number of chromosomes of your parent Bede Bug (haploid number). 5. Now mate with your partner! Combine your 7 cards with your partner’s. This simulates random fertilisation. Remember you could have mated with any other Bede Bug in the class! 6. Congratulations! You are pregnant! Bet you can’t wait to see what your baby is going to look like! It’s time to record your Baby Bede Bug’s genotype (genetic makeup) in Table 2 and work out its phenotype (appearance). 7. TIME TO GIVE BIRTH! Use your data in Table 2 to create your Baby Bede Bug (use figure 1 to help you). 8. When you have finished, we will compare class results. o Are any two Baby Bede Bugs from our class the same? o If not, why not? o What other event during meiosis can create even more genetic variation? 9. If you have time, take the sets of cards (gametes) that you and your partner did not use during fertilization. How would your Baby Bede Bug’s appearance have been different had you used these gametes instead of the ones you chose first time round? Dismantle your Bede Bugs & put your cards back into their original sets. Thank you!