This experiment aimed to determine the effect of female selection on gene frequency in Drosophila melanogaster fruit flies. Virgin female flies with red eyes were crossed with male flies having white eyes, and their offspring were observed over multiple generations. The results showed that female flies mated more often with male flies displaying the same red-eye phenotype, decreasing the frequency of the white-eye gene from 22.72% to 12.31% across generations. This indicates that female selection in Drosophila melanogaster can influence gene frequencies in populations over time by preferring to mate with males exhibiting similar traits.

1. Experiment on Female Selection in
Drosophila melanogaster

2. AIM
To determine the effect of female selection
on gene frequency.

3. INTRODUCTION
FEMALE SELECTION
• Usually female chooses his or her mate
according the desired or attractive characteristics
the selector wants to be represented in his or her
offspring (P. Brennan, 2012).
• Just like in humans, Drosophila melanogaster
fruit flies have preference for those with whom
they wish to mate.
• This force, known as sexual selection, is one of
the main factors that determine the course of
evolution in any particular species.

4. INTRODUCTION
D.melanogaster
Drosophila is one of the first organisms to be studied
genetically: its small size, short life cycle, high
reproductive rate, and ease of culture. Many
different species, and a large number and wide variety
of naturally-occurring and artificially-induced genetic
variants are available.

5. CULTURE MEDIA
For Drosophila, a satisfactory standard culture medium
must be nutritious, inexpensive, have a high moisture
content and a firm texture, and be resistant to mould and
bacterial contamination. Most standard media contain
sugar source, a grain base, agar, a mould inhibitor and
yeast (Ashburner & Thompson,Jr 1978).

6. PROCEDURE
• We were given 2 culture bottles with Drosophila
melanogaster , one set with red-eye color(OK) &
other set of white -eyed mutants.
• Before we set up the cross, we cultured the flies, so as
to increase the fly count.
• The flies were sub-cultured for ten days.
• Approximately we got 150 flies.
• Now we should collect virgin OK females.

8. IMPORTANCE OF VIRGIN FEMALES
All female flies used in controlled genetic crosses must
be “virgins”. Female flies are capable of mating as early
as possible after emerging from the pupae stage and
are polyandrous(capable of mating with several males).
Once mated Females can retain viable sperm for
several days and this will confuse the results of a
subsequent controlled mating. To prevent this, all OK
female pupas are removed from the culture bottle
prior, so that all newly hatched flies will remain virgin.

9. •After collecting the virgins we have to keep for aging.
•Aging is done to know whether the collected virgins are
contaminated or not.
•P1 Cross is set up.
•20 virgin red-eyed female is crossed with 20 white-eyed
males.
P1 generation = 20 OK X 20 white eye
female Male
•We allowed the cross to develop for 10 days.
•Then F1 progenies were isolated and phenotypes were
examined.
•The observed results are as follows:

10. P1 generation = 20 OK X 20 white eye
female Male

11. F1 Generation Result
Red eye female Red eye male White eyed
male
No. of flies 11 6 5

12. 10 F1 Virgin females was crossed with 5 F1 ok males
and 5 white males from the stock.
P2 generation = 10 F1 OK X 5 F1 X 5 white
female Male male

13. RED EYED
FEMALE
F2 GENERATION RESULT
RED EYED
MALE
WHITE EYED
MALE
All white males were discarded
F2 selfing was carried out
WHITE EYED
FEMALE
No. of flies 37 18 20 16

14. F2 SELFING
P3 generation = F2 OK X F2 ok X F2 white
female Male female

15. F3 GENERATION RESULT
RED EYED
FEMALE
RED EYED
MALE
WHITE EYED
MALE
WHITE EYED
FEMALE
No. of flies 55 24 21 20
All white males were discarded
F3 selfing was carried out

16. F3 SELFING
P4 generation = F3 OK X F3 ok X F3 white
female Male female

17. RED EYED
FEMALE
F4 GENERATION RESULT
RED EYED
MALE
WHITE EYED
MALE
WHITE EYED
FEMALE
No. of flies 68 32 17 21

18. DATE12 RED EYED
FEMALE
TOTAL FLIES
RED EYED
MALE
WHITE EYED
MALE
WHITE
EYED
FEMALE
TOTAL
F1 11 6 5 0 22
F2 37 18 20 16 91
F3 55 24 21 20 120
F4 68 32 17 21 138

19. CALCULATIONS
GENE FREQUENCY
Gene frequency = n X 100
Where as,
N
n= no. of white eyed male
N= total no. of progeny

20. CALCULATIONS…
GENE FREQUENCY
WHITE EYED
MALE
TOTAL
POPULATION
SIZE
FREQUENCY OF
WHITE MALE
F1 5 22 22.72%
F2 20 91 21.97%
F3 21 120 17.5%
F4 17 138 12.31%

21. 25.00%
20.00%
15.00%
10.00%
5.00%
0.00%
GENE FREQUENCIES GRAPH
F1 F2 F3 F4
FREQUENCIES

22. 25.00%
20.00%
15.00%
10.00%
5.00%
0.00%
GENE FREQUENCIES GRAPH
F1 F2 F3 F4
GENE FREQUENCIES

23. INTERPRETATION
Our results indicate that female Drosophila
melanogaster preferred to mate with their
own phenotype (male displaying her own
characteristics).
RED MALES ARE MORE IN COUNT
Overall, the number of red male offspring
produced is almost double that of the white
offspring (32:17) in F4 generation.

24. INTERPRETATION …
• A positive effect of Female selection is that it
increases variation within a population.
• Although our results showed that the females
mated more with males of the same
phenotype, they also mated with males that
showed different traits.
• This contributes to increased genetic variation
and prevents complete speciation.

25. INTERPRETATION …
• Conversely, if female D. melanogaster only chose to
mate with males of similar phenotypes, they could
potentially develop into two separate species.
• This is known as disruptive selection, which occurs
when the average of a particular trait in a population
is selected against (i.e. the two extremes are
selected) and causes an entire population to diverge
into two separate populations.
• Thus, the preferences of female D. melanogaster
may cause males to develop useful or detrimental
traits, or may ultimately lead to the development of a
new species.

27. REFERENCE
• https://bu.digication.com/nahomiv/Sexual_Selection
_and_Mating_Preferences_of_Female_
• http://www.ou.edu/journals/dis/DIS60/Ramachandr
a%20171.pdf
• www.googleimages.com

28. THANK YOU