GENERAL BIOLOGY CLASSES
Mendelian Genetics Lab Activity
PRE-LAB QUESTIONS
(Students may not begin the lab activity until these are completed and submitted.)
1. Name each of Mendel’s Laws, and explain what each one means in common English.
2. Draw and correctly label a Punnett square for the following situation:
 One parent plant is homozygous for the dominant seed shape (round seeds),
 While the other parent is heterozygous for the same trait.
3. In the above Punnett Square, give the physical traits (phenotype) for all four possible outcomes.
4. It is possible, and often happens, that two parents with brown eyes could produce a child with blue
eyes. Draw a Punnett Square illustrating this outcome, and compute the odds that it might happen.
5. Following is a partially completed Punnett square for a dihybrid cross. In it, both parents have brown
eyes, but carry the recessive trait for SMA (spinal muscular atrophy – a rare genetic disorder).
 Complete the square.
 Compute the odds of having a child with blue eyes.
 Compute the odds of having a child with blue eyes and SMA.
 Compute the odds of having a child with brown eyes and SMA
 SHOW ALL MATH!
B = brown eyes;
N = normal Central Nervous System development;
b = blue eyes
n = spinal muscular atrophy
FATHER
BN
M BN
O
T Bn
H
E bN
R
bn
Bn
bN
bn
LAB ACTIVITY - EXPLORING GENETIC PROBABILITY
INTRODUCTION:
WHEN A COIN IS TOSSED, IT CAN REALISTICALLY LAND IN ONLY ONE OF TWO
POSITIONS — EITHER HEADS UP OR TAILS UP. WE HAVE LEARNED THAT IN A SIMILAR
WAY, EITHER THE MATERNAL GENE FOR A TRAIT OR THE CORRESPONDING PATERNAL
ALLELE MAY BE TRANSFERRED TO A SINGLE SPERM OR EGG CELL — BUT NOT BOTH. IF
THE PARENT IS HETEROZYGOUS (IF HE OR SHE HAS 2 DIFFERENT COPIES OF A GIVEN
ALLELE), A GAMETE MAY CARRY CODING ONLY FOR THE DOMINANT TRAIT OR ITS
RECESSIVE COUNTERPART.
THE MATHEMATICIAN DESCRIBES THIS SITUATION BY SAYING THAT THE PROBABILITY
OF ONE ALLELE (OR COIN) ENDING UP EITHER WAY IS 50%, 0.5, OR 1/2. (MENDEL
SUMMARIZED THIS IN HIS "LAW OF SEGREGATION.")
IN THIS LAB ACTIVITY, COINS REPRESENTING EACH TRAIT WILL BE FLIPPED IN PAIRS.
EACH COIN STANDS FOR A CHOICE BETWEEN TWO ALLELES THAT MAY BE CARRIED BY
A SINGLE GAMETE (SPERM OR EGG CELL). TWO GAMETES THEN UNITE INTO A
ZYGOTE—THE FIRST SOMATIC CELL OF A NEW ORGANISM.
ONE SIDE OF EACH COIN REPRESENTS ONE POSSIBLE ALLELE SENT FROM ONE PARENT.
A COMBINATION OF TWO “ALLELES” FROM 2 SEPARATE COINS ARE USED TO
DETERMINE THE GENOTYPE AND PHENOTYPE OF THE NEXT GENERATION.
TWO IDENTICAL COINS LANDING IN VARIOUS POSITIONS CAN BE USED TO MIMICK
THE GENOTYPE AND PHENOTYPE OUTCOMES RECORDED BY MENDEL FOR A SINGLE
TRAIT IN A HYBRID CROSS (THE MATING OF TWO HETEROZYGOUS PARENTS.)
SIMILARLY, WE MAY USE FOUR COINS (TWO PENNIES AND TWO NICKELS FOR EXAMPLE)
TO TEST THE GENOTYPE AND PHENOTYPE RATIOS WHICH RESULT FROM A DIHYBRID
CROSS - THE MATING OF PARENTS WHO ARE HETEROZYGOUS FOR EACH OF TWO
DIFFERENT TRAITS.
THIS INVESTIGATION SHOWS THAT PROBABILITY IS STRONGLY RELATED TO GENETIC
OUTCOMES. OUR DATA MAY EITHER SUPPORT OR CHALLENGE THE 19TH CENTURY
DATA AND CONCLUSIONS OF GREGOR MENDEL.
PLEASE NOTE: YOUR HYPOTHESIS MUST BE DIRECTLY RELATED TO THE RESEARCH
CONDUCTED BY MENDEL.
MATERIALS:




PENNIES AND NICKELS;
PERMANENT MARKER;
PENCIL OR PEN;
DATA RECORDING CHARTS
DIRECTIONS:
PART A (USE TABLE A TO ORGANIZE THE DATA.)
IN PEA-PLANT FLOWERS, THE COLOR PURPLE (P) IS DOMINANT OVER WHITE (p).
1. COMPLETE A PUNNETT SQUARE FOR TWO HETEROZYGOUS PARENTS. YOUR SQUARE
SHOULD REFLECT THE CLASSIC 1: 2: 1 (0.25: 0.50: 0.25) GENOTYPE PROBABLITY IN A
HETEROZYGOUS CROSS FOR THIS TRAIT. (MENDEL OBSERVED THIS OUTCOME
MANY TIMES DURING HIS TESTING; RESULTS WERE REPEATED WITH GREAT
PRECISION.)
THIS IS THE FIRST OUTCOME WE WILL EXAMINE. DURING OUR COIN FLIPS:

A HEADS-HEADS COMBINATION WILL REPRESENT A HOMOZYGOUS-DOMINANT
OUTCOME (PURPLE FLOWER - LABEL THE TOP BOX IN THE LEFT COLUMN OF YOUR
TABLE ACCORDINGLY);

A HEADS-TAILS COMBINATION WILL STAND FOR A HETEROZYGOUS OUTCOME
(PURPLE FLOWER - LABEL THE SEC0ND BOX IN THE LEFT COLUMN OF YOUR TABLE
TO REFLECT THIS);

A TAILS-TAILS COMBINATION WILL REPRESENT A HOMOZYGOUS-RECESSIVE
OUTCOME (WHITE FLOWER - LABEL THE LAST BOX IN THE LEFT COLUMN OF YOUR
TABLE TO REFLECT THIS).
2. YOU WILL COMPLETE 100 FLIPS OF TWO COINS. USE 2 PENNIES.
3. BEFORE YOU START, RECORD THE "EXPECTED OUTCOME" IN THE APPROPRIATE
COLUMN OF THE TABLE. (BE CAREFUL; REMEMBER THAT THERE ARE TWO
DIFFERENT WAYS FOR TWO PENNIES TO LAND "HEADS-TAILS." 2 (0.25) = 0.50 )
4. AS THE EXPERIMENT PROGRESSES, MAKE APPROPRIATE HASH-MARKS IN EACH BOX.
5. WHEN YOU FINISH, DIVIDE THE RESULTS OF EACH GENOTYPE BY THE TOTAL OF
TOSSES (100) TO OBTAIN THE “EXPERIMENTAL OUTCOME.”
PART B - A DIHYBRID CROSS
This part of the lab activity is NOT required—it is extra credit—for general biology classes.
IN PART B - AND IN TABLE B - WE WILL REPEAT THE ABOVE EXPERIMENT, THIS TIME
USING FOUR COINS TO EXAMINE A DIHYBRID CROSS. THIS TIME, HOWEVER, WE WILL
COMPLETE 200 FLIPS.
BECAUSE WE ARE LOOKING AT 2 TRAITS, THIS TIME WE WILL NEED 2 DIFFERENT COINS
FOR EACH PARENT. ONE COIN WILL REPRESENT EACH OF THE 2 TRAITS CONTRIBUTED
BY THAT PARENT.

THERE ARE 2 SIDES TO EACH COIN, AND 2 POSSIBLE OUTCOMES FOR EACH TRAIT,
BECAUSE EACH HETEROZYGOUS PARENT CARRIES 2 DIFFERENT ALLELES FOR THE
TRAIT.

ANY 1 OF 4 POSSIBLE COMBINATIONS MAY THEREFORE TURN UP IN ANY SINGLE
SPERM CELL OR EGG CELL — AND THUS THERE ARE 16 POSSIBLE OUTCOMES WHEN
THE EGG AND SPERM (GAMETES) EVENTUALLY MEET.
IN CORN PLANTS:

ROUGH SEED SHAPE (R) IS DOMINANT OVER SMOOTH SEED SHAPE (r)

AND YELLOW SEEDS (Y) ARE DOMINANT OVER WHITE SEEDS (y).
1. CREATE A PUNNETT SQUARE. DETERMINE THE 4 POSSIBLE GAMETES PRODUCED BY
EITHER PARENT. THEN, DETERMINE THE POSSIBLE SEED SHAPE AND COLOR OF ALL
OFFSPRING WHOSE PARENTS ARE EACH HETEROZYGOUS FOR THE TWO TRAITS.
2. OBTAIN TWO PENNIES AND TWO NICKELS.

LABEL THE HEADS SIDE OF BOTH PENNIES "R" AND THE TAILS "r."

LABEL THE HEADS SIDE OF BOTH NICKELS "Y" AND THE TAILS "y."
3. LABEL THE SECOND COLUMN OF THE TABLE (BELOW COIN COMBINATION) WITH
THE CORRECT GENOTYPE(S).
4. LABEL EACH BOX IN THE FIRST COLUMN OF THE DATA TABLE. "PHENOTYPE"
SHOULD REFLECT THE OUTCOMES IN YOUR PUNNETT SQUARE.
5. ENTER DATA IN THE "EXPECTED PROBABILITY" COLUMN FOR EACH GENOTYPE.

COUNT UP THE BOXES IN THE PUNNETT SQUARE THAT MATCH EACH GENOTYPE.
REMEMBER THAT SOME OF THE ALLELES IN YOUR DATA TABLE MAY BE PRODUCED
IN MORE THAN ONE WAY (FOR EXAMPLE, THERE ARE TWO DIFFERENT WAYS TO
PRODUCE "HEADS-TAILS" IN THE FLIPPED PENNIES, AND TWO DIFFERENT WAYS TO
PRODUCE "HEADS-TAILS" IN THE NICKELS)

(NUMBER OF PUNNET SQUARE BOXES
THAT MATCH ONE GENOTYPE) . =
(16)
PROBABILITY OF THAT OUTCOME.
6. TOSS THE COINS 200 TIMES. RECORD THE RESULTS OF EACH TOSS USING HASH
MARKS. WHEN YOU FINISH, DIVIDE EACH RESULT BY THE TOTAL (200) TO OBTAIN
THE EXPERIMENTAL PROBABILITY THE OUTCOME OF THIS ACTIVITY.
OBSERVATIONS AND CONCLUSIONS:
1. HOW CLOSELY DID YOUR DATA RESEMBLE THE EXPECTED PROBABILITY FOR THE
MONOHYBRID CROSS? DO YOUR DATA SUPPORT THE DATA AND CONCLUSIONS
PUBLISHED BY MENDEL?
2. DO YOUR DATA MORE CLOSELY MATCH MENDEL’S FOR THE DIHYBRID CROSS THAN
THEY DID IN PART A (A MONOHYBRID CROSS?) WHATEVER YOUR ANSWER, EXPLAIN
WHY YOU OBTAINED THE OUTCOME YOU DID. (WHY DO THE DATA FROM PART B
MATCH MENDEL’S MORE CLOSELY—OR LESS CLOSELY—THAN THE MONOHYBRID
CROSS IN PART A?)
3. STUDENTS ALMOST NEVER OBTAIN A PERFECT MATCH FOR THE EXPECTED
OUTCOMES. WHY DO YOU THINK THIS IS SO?
4. IF YOU INCREASED THE NUMBER OF COIN FLIPS TO 500 OR 1000, DO YOU THINK
YOUR DATA WOULD MORE CLOSELY OR LESS CLOSELY MATCH MENDEL’S RESULTS?
WHY?
5. EXTRA CREDIT: COMLETE A PUNNETT SQUARE FOR ANY TRI-HYBRID CROSS
DATA TABLE A—MONOHYBRID CROSS
Phenotype
Coin Combination
PENNY
HEADS
PENNY
HEADS
GENOTYPE(S)
PENNY
HEADS
PENNY
TAILS
GENOTYPE(S)
PENNY
TAILS
PENNY
TAILS
GENOTYPE(S)
Tally
Expected
probability
Experimental
outcome
DATA TABLE B
Phenotype
Rough,
Yellow seeds
Coin Combination
PENNY
HEADS
PENNY
HEADS
GENOTYPE(S)
RR only
PENNY
HEADS
PENNY
HEADS
GENOTYPE(S)
RR only
PENNY
HEADS
PENNY
TAILS
GENOTYPE(S)
Rr or rR
PENNY
HEADS
PENNY
TAILS
GENOTYPE(S)
Rr or rR
PENNY
HEADS
PENNY
HEADS
GENOTYPE(S)
RR only
PENNY
HEADS
PENNY
TAILS
GENOTYPE(S)
Rr or rR
PENNY
TAILS
PENNY
TAILS
GENOTYPE(S)
rr only
PENNY
TAILS
PENNY
TAILS
GENOTYPE(S)
rr only
PENNY
TAILS
PENNY
TAILS
GENOTYPE(S)
rr only
NICKEL
HEADS
Tally
NICKEL
HEADS
GENOTYPE(S)
YY only
NICKEL
HEADS
NICKEL
TAILS
GENOTYPE(S)
Yy or yY
NICKEL
HEADS
NICKEL
TAILS
GENOTYPE(S)
Yy or yY
NICKEL
HEADS
NICKEL
HEADS
GENOTYPE(S)
YY only
NICKEL
TAILS
NICKEL
TAILS
GENOTYPE(S)
yy only
NICKEL
TAILS
NICKEL
TAILS
GENOTYPE(S)
yy only
NICKEL
HEADS
NICKEL
HEADS
GENOTYPE(S)
YY only
NICKEL
HEADS
NICKEL
TAILS
GENOTYPE(S)
Yy or yY
NICKEL
TAILS
NICKEL
TAILS
GENOTYPE(S)
yy only
Expected
probability
Experimental
probability
(Outcome)
1  16 =
0.0625
(tally) 
200 =