Title: How mutated alleles act on living things external features ?
Students researchers: Brelle Myriam and Denet-Daveau Léa
School address: Lycée Romain Rolland
17, rue Lucien Nadaire
94200 Ivry sur Seine
France
Grade: Seconde générale (section européenne)
Teachers: Martine Pernodet and Nathalie Octo
I)
Statement of purpose and hypothesis
We are working on mutations. We know that a mutation is a change in the DNA sequence of a gene
that can alter the amino acid sequence of the protein encoded by the gene, which is responsible for
the features of the cells.
We would like to know how mutated alleles change external features. Our hypothesis is that only
one mutated allele can change a living thing external feature.
II)
Methodology
To test our hypothesis, we are going to observe one feature of drosophilae (fruit fly): their eyes
colour. As students, we cannot mutate DNA of drosophilae, so we are going to work on their
pairing.
In general, drosophilae have red eyes but
some of them have white eyes. The
drosophilae on which we are going to
investigate are pure race drosophilae i.e.
their eyes colour have been the same for
many generations before. That is why we are
sure that they have the two same alleles of the
gene responsible for the eyes colour on their
two chromosomes. By making a red-eyed
drosophila mating with a white-eyed
drosophila we are going to have offspring with
an allele for white eyes and an allele
for red eyes because during the
fertilization each parent gives one
chromosome of each 4 pairs it owns.
a) Drosophilae’s food preparation
Materials:
-bent glass
-phial
-microwave
-a pestle
-1.2g of agar
-5.6g of sucrose
-1g of moldex
-10mL of alcohol
-1.6g of baker’s yeast
-a half banana
Protocol:
-Pour 60 ml of water in the bent glass and bake it in the microwave.
-Put 1.2g of agar in the cool water. Add 5.6g of sucrose and mix with the pestle.
-Bake the mixing in the microwave for 1 min.
-Take it out of the microwave and let it get cool.
-Pour 1.6g of baker’s yeast in the cool mixing.
-Dissolve 1g of moldex in 10mL of alcohol in a phial and then, pour it in the mixing.
-Peel and crush a half banana with a fork and put it in the mixing.
-Mix with the pestle.
-Divide it in four culture tubes.
-Let it become hard.
b) Drosophilae insertion in the culture tubes
Materials:
-About 20 white-eyed drosophilae
-About 20 red-eyed drosophilae
-A phial
-Watch glasses
-Ether
-A lamp
-Cotton
-A funnel
-A pipette
-A microscope
Protocol:
-Put the funnel above the phial.
-Pour some ether drops on a piece of cotton.
-Quickly put the 20 white-eyed drosophilae in the phial and immediately fill in with the piece of
cotton and cover with a watch glass to prevent drosophilae from going out.
-Let them fall asleep.
-Put the sleeping drosophilae in watch glasses.
-Observe them with the microscope.
-Separate the males from the females (males have short dark abdomen whereas females have bigger
and lighter one).
-Do the same operation with the 20 red-eyed drosophilae.
-Then in each two culture tubes, put 3 white-eyed females with 3 red-eyed males and in each two
other culture tubes, put 3 red-eyed females with 3 white-eyed males.
-Wait several weeks and see.
III)
Analysis of data
We have observed the sleeping drosophilae’s offspring with the microscope and noted that they all
have red eyes despite they all have one allele for white eyes and one allele for red eyes. This means
that only the allele for red eyes had been expressed. However, the allele for white eyes is working
too since some drosophilae have white eyes. So the allele for white eyes works only if the allele of
the other chromosome is for white eyes too. We can conclude that alleles for red eyes are dominant
on allele for white eyes.
IV)
Summary and conclusion
By this experiment, we have shown that some alleles of one gene are dominant on others. So by
mutating only one allele, we are not sure that it will have consequences on the cell features. To
change a living thing external feature, we have to check that either the mutated allele is dominant or
it is present twice.
V)
Application
Living things usually undergo natural mutations most of the time during DNA replications because
of errors, which are not corrected. These mutations have not always consequences on living thing
features because of the dominant alleles. But living things can pass on their mutated allele to their
offspring and features resulting to these mutations can appear on them in the next generations.
Mutations are involved in evolution.