“So all the cells have broken up and the DNA has come out and is in that liquid?”
“That’s right, Harry. Now we’re going to put the tubes in the water bath.” She pointed at a rectangular box with a black lid. There was a number lit up in red lights on the front that said “60ºC” and a loud whirring sound coming from the machine. “The water is really hot and will heat up the samples,” said Annabelle. “That will totally destroy any cell membranes that are left and all the DNA will be released.”
“We’ve totally blasted the cells!” said Harry in delight. Annabelle set the timer for ten minutes. When the time was up she took the tubes out of the water bath.
“Now we need to put the liquid from each sample through a filter.”
“What’s a filter?” Annabelle showed Harry the special tubes with the filter inside which looked like a very small piece of paper. She transferred the liquid from the first set of tubes into the filter.
“A filter is like the sieve Mum puts flour in when she makes cakes to get the lumps out. All the broken up bits of cell get caught in the sieve. The DNA which is dissolved in the liquid goes right through the sieve. Harry watched as a clear liquid slowly dripped out of the bottom of the filter and into another tube. They waited patiently until it had all collected in the bottom of the tube.
“Now to add the alcohol!” said Annabelle. Harry felt his nose tingle as Annabelle added the alcohol. The smell was really strong.
“The salt in the DNA extraction buffer we added at the start makes the DNA clump together and the alcohol makes the DNA come out of solution. If you watch the tube as I tip it gently up and down you will see the DNA appear,” explained Annabelle. “There it is! Can you see the white strands?” Harry watched as the two liquids swirled together like ice cubes melting into water. Then suddenly very thin strands like white cotton appeared. It was so exciting. One minute the tube contained only a clear liquid, the next what looked like a ball of white cotton appeared as if by magic!
“How cool is that? Look Annabelle – we have DNA in all our samples. That’s amazing!” Both children were delighted. Their eyes sparkled.
“We just have to hook the DNA out with this little plastic hook and put it in this last liquid. This will make sure the DNA is really clean and it can be stored for a long time without being destroyed. If we leave them in the fridge Mum will think they’re her samples and will get the results for us. We are finished Harry!” The children quickly cleaned up making sure they left everything as they found it. They ran out of the laboratory and into the lounge to check on Granny. She was still asleep!
“I wish Mum would come home soon so we can get the results. I just hope they’ve worked,” whispered Annabelle to Harry. Both children crossed their fingers.
When Mum and Dad returned later that day Mum proudly announced “I’m going to take the rest of the day off. No lab work till tomorrow!” Annabelle looked at Harry and could see he was as disappointed as her.
“We really need those results” said Harry.
“I know, but hold on a minute,” said Annabelle. “Maybe the delay could be just what we need.” She suddenly looked very pleased with herself.
“I don’t understand,” said Harry.
“Well, I just had a thought. If we could get some fur from Issy and Peter’s dogs Scally and Poppy and from Milly we could get DNA from them. If we got DNA from the fur we found in the shed and compared them then we could prove they were in the shed and that it was Milly’s fur on the fence!”
“Great idea!” said Harry. The children ran to the kitchen and got a sandwich bag. They then found Milly’s brush in the kitchen drawer.
“We need fur with a root on them. You’re looking for a little round bit at the end of the hair Harry.” They examined the brush carefully and put the hairs into the bag which they labelled “Milly”.
“Mum! Can we go round to Issy and Peter’s houses to play?” they both pleaded. When Mum wasn’t looking Harry winked at Annabelle and she laughed. Mum was completely oblivious to their plan. Annabelle looked at the plastic bag sticking out of Harry’s pocket and squeezed the bag in her pocket. Not long now and they would have fur from Scally and Poppy as well as Milly. Then they would break into the lab later and get DNA from the dog’s fur.
Soon they would have the proof that Mr Baker had stolen their pets and had kept them hidden in the shed. Her heart pounded with excitement. The results would be ready when they got home from school tomorrow. “Please let the time go quickly,” Annabelle whispered to herself.
s soon as they got home from school Annabelle and Harry ran to the kitchen. They looked on the shelf where Mum always left her results ready to post to her clients. Sure enough there were two brown envelopes. Now all they needed was a diversion.
“Watch this!” said Harry, full of glee. He picked up a box of Cheerios and took them into the lounge. Annabelle heard the noise as the entire box was emptied onto the floor followed by a loud cry.
“Mum!” he shouted. Annabelle watched as her mum ran into the lounge and shouted in dismay at Harry. This was her chance. She grabbed her notepad from her book bag and looked up the numbers of their samples. She opened the envelopes, found the correct numbers for the results and took them out. One envelope had the results for the animals, the other for humans. She put the results into her book bag and carefully replaced the envelopes. Quickly she then went into the lounge and helped clear up the rest of the Cheerios which had spilt everywhere!
“Come on, let’s go and look at the results,” said Annabelle as soon as Mum had left the room. Harry pushed past her, grabbing the book bag from her hand. She laughed as she saw a cascade of Cheerios falling out of his top and trousers as he climbed the stairs. She carefully picked them up as she followed behind him.
“What do the results mean?” he asked as Annabelle entered her bedroom.
“Hold on a minute. You’ve mixed them all up.” Annabelle spread the results out. Using the information in her notepad she sorted them into groups. “Okay, these are the results from the dogs,” she said.
“We need to compare these results which have the DNA from the fur we found in the shed with these ones which have the DNA we got from Scally, Poppy and Milly. If they match then we know they were in Mr Baker’s shed,” explained Annabelle.
“Like a game of snap,” said Harry.
“Exactly!” said Annabelle as she spread out the paper which had the results in front of them. The results from the fur they found in the shed were at the top. The results from the dogs were at the bottom. They both moved forward so they could look closely at the results. On the paper were lots of different coloured peaks and each peak had a different number.
“Snap!” said Harry “Wow! Look these two are the same. Quick look the samples up. Whose sample is it?”
“It’s Scally! She was in the shed!” said Annabelle excitedly. “This one matches too… it’s… hold on… it’s Poppy!” Annabelle dared not look at the last one. She opened one eye and held her breath.
“The last one is a match,” announced Harry. He watched Annabelle check the notepad. She beamed.
“It’s Milly!” she hugged her little brother and they danced around the room.
“What about the fur on the fence?” asked Harry. Annabelle found the result for that sample.
“It’s a match with Milly! So Milly’s fur must have got caught on the fence when she was taken from our garden,” said Annabelle.
“What about the blood?” Annabelle found the results for the cotton bud taken from the blood they had found on the fence.
“Oh! It didn’t work for dog DNA. The paper she held up had no peaks on it. Hold on it worked for human DNA. It’s from a human and it’s from a man!” exclaimed Annabelle her eyes wide with excitement.
“How do you know that?” said Harry.
“Look at this bit of the pattern here,” Annabelle pointed to two green peaks. “Can you see they’re labelled ‘X’ and ‘Y’?”
; “Yes!” replied Harry staring at the results.
“Well if you’re a male, a boy you will have an ‘X’ and a ‘Y’ and if you’re female, a girl you’ll only have an ‘X’. It’s the ‘Y’ bit which makes you male. It’s the bit of DNA which contains all the instructions to make a male. Girls don’t need that bit.”
“So we definitely know whoever stole Milly was male and that the blood from the fence wasn’t from Milly. What a relief!”
“Let’s have a look at the other results,” said Annabelle. She spread out the results from the cigarette, hat, glove, syringe, the door handle and the cages. “I expect the results will all match the results from the blood, they will be from the same person.”
“You’re right! These results match the person who left their blood on the fence,” said Harry. “What are they from?” Harry watched as Annabelle looked at her notepad.
“They’re from the cigarette we found in the garden and the syringe. That must have been Mr Baker too.”
“But look at these results. There are lots of peaks. Almost double the amount of peaks than in the other results,” Harry pointed to another set of results. The children looked and then looked at each other. The results were not as they expected.
“They’re from the door handle and the cages. I don’t understand. Look Harry – this pattern of peaks from the hat and the glove – it’s different from the results for the DNA from the blood.”
“But still from a male,” said Harry. As he pointed to the X and Y peaks the penny dropped and they both said together: “There are two men!”
“That’s why we have so many peaks on the door handle and from the cages. They’ve both touched these places. So the DNA from both of them is here.” The children were delighted to have so many clues! They high fived each other.
“I wonder which of the results is Mr Baker? And who is this second person?” Annabelle put the results next to one another. “There are a lot of similarities in the patterns from these two,” she said. “You see the numbers for the peaks – they share a lot in common. Mum says that when you’re a born you get half your DNA from your mum and half from your dad. I think these two might be related.”
“Mr Baker has got a son,” said Harry.
“That would make sense. That’s why the hairs in the hat didn’t match Mr Baker. They were from his son!”
“This is so exciting. We’ve nearly proved it all, Harry. There is one more thing we need to do.”
“What’s that?” enquired Harry.
“Get a sample of DNA from Mr Baker and his son,” said Annabelle
“And how ever will we do that?” said Harry. They looked at each other. It seemed an impossible task. But, to complete the last bit of the jigsaw and prove Mr Baker and his son had taken Milly, surely they had to find a way.
he next morning at breakfast Annabelle and Harry excitedly handed an invitation they had made to Mum. Annabelle smiled to herself. She remembered the moment last night when she’d spotted an invite to Issy’s birthday party and the idea had come to her. What if they invited Mr Baker and his son to come over for tea and cake after school to say sorry for breaking into his shed? Then they could easily get DNA from both men from anything that they touched and from their coats. Harry had thought it was a great plan. They had made and coloured in the invitation together.
Now Annabelle watched her mum anxiously as she read the invitation trying to guess what her decision would be.
“I think that’s a lovely idea, you two. Why don’t you go and post it now?” said Mum.
Annabelle felt so relieved. She watched as Harry snatched the invitation from Mum’s hand and ran off to Mr Baker’s house. He was so quick! Now they would have to wait the whole day to see if the men would agree to come!
The day had passed so slowly but finally here they were waiting by the window to see if Mr Baker and his son would come. Annabelle looked at Harry who was bored. She watched as he squashed his nose against the glass and wiped his face up and down the window.
“That’s so gross, Harry. Look at the mess you’ve left on the glass!”
“Yes, but look how flat I can make my nose,” said Harry. “Have a go!” They were so busy they almost didn’t see Mr Baker and his son as they walked up the path towards the front door. The knock on the door made them jump.
“So pleased you could come,” said Mum showing them into the lounge. “Annabelle and Harry – why don’t you get the cakes?”
“Can I take your coats?” said Harry. He winked at Annabelle. She knew he was going to try and get some DNA from the coats like they’d planned. Fingers crossed! Now it was her turn. “Please let this work!” she thought. It really was the very last piece of the jigsaw. If they could get DNA from Mr Baker and his son and match it to the samples from the shed and the garden they could prove the men had taken the dogs.
“Cup of tea for you both?” asked Mum. “Annabelle, why don’t you get the chocolate cake?”
Annabelle watched excitedly as the men drank from the cups and used a fork to eat their cake. She remembered what Mum had told them in the forensic workshop: “every contact leaves a trace!” She visualised the cells in their mouths being rubbed off as they ate and drank. All that saliva containing cells being left on the cup and fork. All those cells containing DNA! Please let there be enough.
Meanwhile Harry was very busy. By a stroke of luck Mr Baker had worn the same boots that the children had seen in his house. He had taken them off and left them in their porch when he went inside. They were the boots the children suspected he had been wearing when he stole Milly and had left the footprint in their garden. Harry picked up the left boot and took it into the office which was opposite the lounge. He photocopied the bottom. He was so excited. “I know this boot will match the footprint we found in the garden,” he thought. “More proof.”
He carefully replaced the boot, put on a pair of gloves and then checked the pockets of the coats. There was no way he would contaminate the evidence with his own DNA! In Mr Baker’s coat he found a syringe. He quickly put it into the plastic bag he had hidden in his pocket. Then he used a cotton bud to wipe around the collars and cuffs of both coats. He remembered these were the points where the fabric would rub against the skin, rubbing off all those cells! These bits of the coat would give them the best chance of getting DNA.
Lastly he dug out the Sellotape and pressed the sticky part of the tape onto the coat around the collar. He was delighted. He was able to collect hairs from both coats. He knew he had done well. After hiding the samples upstairs in Annabelle’s room he smugly sauntered into the lounge to gloat.
“We’re so sorry for breaking into your shed,” said Annabelle to Mr Baker. She had her fingers crossed behind her back as she didn’t mean it.
“I hope you like your cake,” said Harry.
“It’s lovely thank you. I think we can forget what happened, don’t you?” said Mr Baker.
Annabelle looked at Mum. She looked relieved.
“Have you finished? Can I take out your cups and plates?” said Annabelle so innocently that there was no way the men could know the trap and that the children had planned to collect their DNA!
“How lovely, thank you,” said Mr Baker. He was smiling and being so nice. The children could see that Mum had fallen for it but they had not. Mr Baker’s son remained quiet. He watched the children closely but they were not phased. How could he possibly guess what they were doing? The children were both looking at his hair. Unlike Mr Baker his hair was long and black. Just like the hairs they had found in the baseball cap they found in the garden! Annabelle gave Harry a knowing look.
Annabelle pulled her jumper over her hands to hide the gloves she had put on and carefully picked up the cups and plates. She didn’t want to contaminate them with her own DNA. She was careful to remember not to touch the fork and to remember which person the items had come from.
Once in the kitchen Annabelle used the cotton buds to wipe the cups the men had drunk from an
d the forks they had used to eat their cake. She carefully labelled the bags and then ran upstairs to hide them in her room. She smiled with delight when she saw the samples Harry had collected. She spotted the photocopy of the footprint. Her tummy flipped over with excitement. It was an Aladdin’s cave of evidence! With shaking hands Annabelle pulled out the plaster cast of the footprint they found in the garden. She placed the photocopy next to it. She almost dared not to look. The imperfections where the sole of the boot had been damaged matched perfectly. Mr Baker had been wearing these boots when he had come into their garden to take Milly! She ran as fast as she could downstairs to tell Harry.
“It’s a match!” whispered Annabelle when Harry came out into the kitchen. “The boot is a match! Harry, we have so much evidence. We can get into the lab tonight and get the DNA. Mum is in the lab tomorrow processing samples so we should have the results when we get home from school.”
“I can’t believe you compared the footprints without me. I wanted to do that. I made the photocopy,” said Harry, crossly.
“But they match, Harry. Isn’t that brilliant? We’ll have DNA evidence to prove it was Mr Baker and his son very soon. Did you see Mr Baker’s son has long black hair?”
Harry couldn’t stay cross for long – this was amazing. Both children were so excited. This was it, the last piece of the jigsaw puzzle. Their hearts raced as they danced with each other around the kitchen. They had collected DNA evidence from right under the very noses of the criminals!
s soon as they were home from school Annabelle and Harry ran into the kitchen to see if the envelope was there. It was! Soon they would have the last piece of the jigsaw in their hands. The excitement was almost too much. “Okay, I’ll distract Mum,” said Harry. “Watch this!”
“Mum! Where’s my Star Wars T-shirt? I need it!” Annabelle heard the sound of footsteps running up the stairs to Harry’s room. Quickly she got the notepad out of her book bag and checked the numbers. She then got the results from the envelope. She could see they had worked. Carefully she re-sealed the envelope and put the results into her book bag. Then she went to find Harry.
To Catch a Thief Page 5