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All the information you will need to complete this murder mystery can be found on this sheet.
GOOD LUCK SHERLOCK !!!
Background
They found Lord William’s body in the library, sprawled
on the floor with a dagger in his chest. A copy of his new
will, leaving all his money to charity, was found unsigned
on his desk. The wealthy Lord Williams was a bachelor
who had no family other than his twelve nephews and
nieces. His parents and siblings were all dead.
Inspectors Crick and Watson were the first officers to
arrive on the scene. Before becoming a detective, Crick
had dabbled in genetics. Glancing at the portrait of Lord
William’s parents above the fireplace, Inspector Crick
explained to those assembled that Lord Edward
(William’s father) had bright red hair, caused by a
recessive pair of alleles, while Lady Iris (his mother) had
brunette hair, caused by a dominant allele. Crick further
noted that Iris must have been heterozygous, because
half or her children had been redheads.
Crick and Watson questioned the family and servants
and discovered that there was a witness to the murder.
Remember:
You are looking at TWO traits
On the fateful evening a maid, upon hearing sounds
coming from the library, had spied through the keyhole
and seen someone wearing a long, hooded black cape.
“I could not tell if it was a man or a woman, sir,” she
explained, “but I did see red hair sticking out from under
the hood. The person was holding a dagger behind his
or her back and I noticed that the little finger of that hand
was crooked. It was bent inward toward the fourth
finger.”
“Aha! It’s elementary, Inspector Watson!” Cried Crick. “A
bent little finger is due to a single pair of alleles. If a person
carries just one copy of the dominant allele, they will have
a bent little finger,” Inspector Crick quickly became
convinced that the culprit was a niece or nephew who
stood to lose an enormous fortune if the new will was
signed. To confirm his suspicions, Crick examined old
family photographs and portraits, and assembled a
pedigree chart (found on the back of this page).
1) Hair Colour &
2) Shape of the little finger
In Order to complete this case study, there are some things that you will need to determine:
1.
Use the letter “B” for hair colour and “F” for the shape of the little finger. (½ each = 5 marks TI)
Let B represent _______________________
Let b represent _______________________
Thus:
BB = _______________________
Bb = _______________________
bb = _______________________
Let F represent _______________________
Let f represent _______________________
FF = _______________________
Ff = _______________________
ff = _______________________
Locate the murder victim (Lord William) on the pedigree chart as well as his nieces and nephews (as one of
them is the murderer).
2. Determine the genotype of ALL the individuals in the pedigree chart.
Each individual has only one possible genotype.
Write this genotype directly ABOVE each name in the chart. (½ each = 14 marks TI)
3. Create 12 Punnett squares (one for each marriage shown in the 2nd generation) to show your work in
determining the genotypes of each member of the third generation. (12 marks TI)
(Do not forget to label each square with the name of one of Lord William’s siblings.)
4. Examine the genotypes that you have assigned to each member of the 3rd generation in the chart.
You must indicate their phenotype for the shape of their little finger. (12 marks APP)
Write this phenotype directly BELOW each name in the chart.
Summary Questions:
1. Who murdered Lord William? (! 4 marks APP !)
2. Why didn’t Inspector Crick suspect any of Lord William’s brothers or sisters? (2 marks APP)
3. What role did the dominant allele play in unmasking the perpetrator? (2 marks APP)
4. Why is David not a suspect? (2 marks APP)
/31 INQ
________
/22 App
______
Lady Iris
Brown Hair
Straight Finger
______
_______
______ _______
Wife Edmund
Brown Red
Straight Straight
Catherine
Brown
Bent
Wife
Jeff
Brown Brown
Straight Straight
______
________
Lord Edward
Red Hair
Bent Finger
_______
Husband Margaret
Brown Red
Straight Straight
______
______
______
Husband
Red
Straight
Gertrude
Brown
Bent
Husband
Brown
Straight
_____
Mary
Red
Bent
______
_____
_____
Lord William
Wife
Red
Red
Straight
Straight
Charles
Brown
Straight
________
________
________
_______
_______
_______
________
_______
_______
______
______
______
Douglas
Red
________
Anne
Red
________
Sarah
Brown
________
David
Red
_______
Maude
Brown
_______
Arthur
Brown
_______
Abraham
Brown
________
Joanna
Red
_______
Richard
Brown
_______
Timothy
Brown
______
Chris
Red
______
James
Brown
______
Note: Not all of the third generation genotypes or phenotypes are definite. Use the family background story as well as the F1 generation punnett
squares to make the most logical choice.