Students are introduced to the problem of identifying missing persons. They read a fictional story of children that have been separated from their parents during a war. Their job is to help reunite the parents and children through a scientific investigation. Students are comparing the pros and cons of using blood typing compared to DNA fingerprinting and ultimately answering the question: Which method is more effective in identifying missing persons?
DNA (Deoxyribonucleic acid) is a chemical structure found in the chromosomes which are found in the nucleus of the cell; it’s a piece of a chromosome that dictates a particular trait otherwise known as a gene. DNA is a double helix structure. It looks like a twisted ladder; two strands of genetic material are spiraled around each other. Each strand contains a sequence of bases (also called nucleotides). A base is one of four chemicals (adenine, guanine, cytosine and thymine). The two strands of DNA are bonded at each base: Adenine (A) will only bond with thymine (T), and guanine (G) will only bond with cytosine (C).
DNA fingerprints provide strong evidence for identification, paternity testing and criminal identification. Every individual has a unique chemical makeup or "barcode" of these chemicals. Scientists extract the DNA from a cell, place it in an agar gel and use electricity to move the DNA. The longer pieces move faster than the slower pieces. The DNA is then stained and the result looks like a bar code. Some bands are darker and others are lighter.
Blood Type is a classification of blood based on the antigens and antibodies in red blood cells. The antigens are located on the surface of the red blood cells and the antibodies are in the blood plasma. Individuals have different types and combinations of these molecules. The blood group you belong to depends on what you have inherited from your parents. Each blood type is either positive "+" (has the Rh protein) or negative "-" (no Rh protein). This method of testing is less expensive than DNA fingerprinting but does not give an exact match for identification purposes.
Two copies of the blood type genes are inherited to the offpsring, one from each parent. The possible combinations of alleles produce blood types in the following way:
Blood Type Alleles
Type A AA or AO (A is dominant over O)
Type B BB or BO (B is dominants over O)
Type AB AB (A and B are co-dominant)
Type 0 OO (O is recessive)
For part of this lesson, students will be examining vials of "blood". The blood vials are just for a visual and will have to be labeled by the teacher to show different types, but the mixtures are not different. All the "blood" will look and be the same but the students will be able to tell them apart by the labels. The fake blood is just to increase student interest, engagement and create a visual.
For Blood Typing Station
- Naomi (Mother):A
- Gabriel (Father): O
- Girl 1: AB
- Girl 2: A
- Girl 3: O
- Girl 4: B
- Boy 5: AB
- Boy 6: A
- Boy 7: AB
- Boy 8: O
For DNA Fingerprinting Station
*NOTE: Only cut out children's strips. Place parents DNA fingerprints sheet on the table so the students can place the children's DNA fingerprints in the dotted rectangular box in between the two parents.
" Naomi and Gabriel lost their children about three years ago. The war in their village was devastating, their home and all their possessions were destroyed but nothing compared to the loss of their two children. Enemy troops invaded their village and during the conflict, their two children, Alex and Sophia went missing. Naomi and Gabriel managed to escape, but their two young children were captured. They searched and waited for three very long and tiring years traveling back to their village but there was no sign of them.
Recently, the local police have helped another couple find their children in a village about two hours away. Naomi and Gabriel were hopeful and hired the police’s best detective to travel with them to look for evidence. When they reached the village, the authorities told them they had found some adopted refugee children that came over about three years ago after the war. The children were quickly adopted and evidence suggests they were originally from Naomi and Gabriel’s village. The families who adopted them have been taking good care of them and love the children very much but Naomi and Gabriel want to find their children. They need the help of genetic experts, including you, to help identify their children from a group of ten adopted children.
Two methods of identifying children of specific parents are to look at their blood and DNA. By matching up blood types they can figure out which children are possible matches and which children cannot be matches. The couple also discusses trying to match their DNA fingerprints. They know that DNA needs to be extracted from the cells, cut and stained in a lab. This test is significantly more expensive that blood typing but can provide strong evidence in identification. It can be collected from the children’s blood, teeth or even hair. Your job is to investigate both methods in order to help identify these missing children."
Note: Students may have difficulty matching up the bands of DNA. It's very important to explain that the children's DNA fingerprint must fit exactly in the dotted rectangular box in between the two parents’ DNA fingerprints. Line up the bottom of the rectangular strip. The part that says: Girl 1 is NOT part of the DNA fingerprint
Students can use a punnett square to figure out the allele combinations versus using the computer blood typing calculator. Previous practice and a clear understanding of punnett squares would be necessary.
Please see Project Rubric.
Students will answer analysis questions in their lab notebooks.
Students will choose a method (DNA fingerprinting or Blood typing) and create an "all you need to know" pamphlet about their chosen method, listing the pros, cons, estimated costs, and effectiveness.
The pamphlet can be assigned as an at home project or a classwork assignment if you want to monitor student progress. A suggested rubric for the pamphlet is attached.
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