Download Finch Lab

Do not write on this paper!!
Galapagos Finches:
A Game of Survival and Reproductive Success
Introduction:
In this activity, you will study a population of Darwin finches that
live on Daphne Major, a small island off the coast of Santa Cruz Island in the Galapagos
Archipelago. The vegetation on this island produces both small and large seeds which serve
as the food source for the birds. You will observe how beak size may affect the survival of
some of the finches on the island.
Within this population, there is variation in beak size. Some individual birds have large
beaks and some have small beaks. Assume that the allele for a large beak is “B” and the
allele for a small beak is “b’. Large beaks are dominant.
Recently, a La Nina event occurred, causing a severe drought on Daphne Major and some of
the other Galapagos Islands. All of the plants that produce small seeds have been wiped
out. Therefore, finches with small beaks that are not able to eat larger seeds die of
starvation. They do not reproduce and pass on their genes to the next generation.
Problem:
What will happen to the frequency of the allele that determines the characteristic for
small beak size in an isolated population of finches when all small seed producing plants are
wiped out?
Hypothesis:
On your lab paper, state a hypothesis to predict what will happen to the lethal recessive
gene after 10 generations in a closed population. You should write your hypothesis as an “If.
. .then. . . “ statement to answer the problem question.
Materials:
50 red beans
50 white beans
1 paper bag
3 petri dishes
Procedure:
1. Let 50 red beans represent the allele for large beaks and 50 white beans represent
the allele for small beaks the finch population.
2. Let the paper bag represent the entire finch gene pool on the island of Daphne Major.
3. Label one petri dish ‘B’ for the dominant allele. Label a second petri dish ‘b’ for the
recessive allele. Label a third petri dish ‘RIP’ for those not naturally selected to
survive on large seeds.
4. Place the 50 red beans and the 50 white beans in the paper bag and shake up (mate)
the finches. Don’t Look!
5. Select two alleles (beans) at a time and record in your chart next to Generation #1
each individual (combination of alleles or genotype) finch produced. For examplet to
red beans would be a tally mark under BB. Sort the dominant and recessive alleles
resulting from BB and Bb genotypes into petri dishes #1 and #2. All homozygous
recessive (bb) baby finches unfortunately get placed in dish #3, the RIP graveyard.
Continue this procedure until all alleles (beans) have been counted and sorted.
*** Once in the RIP graveyard, these alleles are no longer able to be passes on to the
next generation. They will stay in the graveyard and not return to the gene pool
(brown paper bag). So sad!
6. Count and record from petri dishes 1 & 2 the ‘B’ and ‘b’ alleles obtained and place in
the chart. Total the number of ‘B’ and ‘b’ for the first generation and record this
number also.
7. Place the alleles (from petri dishes 1 & 2) of the surviving finches; which have grown,
survived and reached reproductive age, back into the gene pool (paper bag) and mate
them again to get the F2 generation.
8. Repeat steps 5, 6, and 7 to obtain generations 2 – 10. Remember: all ‘bb’ individuals
become part of the RIP graveyard and therefore cannot reproduce.
9. Determine the gene frequency of ‘B’ and ‘b’ for each generation and record in the
chart.
To determine the gene frequency:
 # of ‘B’ / Total = allele frequency of ‘B’ (expressed as decimal to the
hundredths place)
 # of ‘b’ / Total = allele frequency of ‘b’ (expressed as decimal to the
hundredths place)
 the frequency of ‘B’ and ‘b’ = 1 (all the alleles for beak size in the population)
10. Plot your frequency of ‘B’ and ‘b’ on one graph using a solid line for ‘B’ and a dotted line
for ‘b’. Label the y-axis “Allele Frequency” and the x-axis “Generations”.
11. Answer the Analysis questions in complete sentences and write a conclusion.