Experiment on Female Selection in Drosophila melanogaster

To determine the effect of female selection on gene frequency.

AIM

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 melanogasterfruit 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.

INTRODUCTION

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.

INTRODUCTION

D.melanogaster

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).

CULTURE MEDIA

• 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.

PROCEDURE

All female flies used in controlled genetic crosses mustbe “virgins”. Female flies are capable of mating as earlyas possible after emerging from the pupae stage andare polyandrous(capable of mating with several males).Once mated Females can retain viable sperm forseveral days and this will confuse the results of asubsequent controlled mating. To prevent this, all OKfemale pupas are removed from the culture bottleprior, so that all newly hatched flies will remain virgin.

IMPORTANCE OF VIRGIN FEMALES

•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.

•We allowed the cross to develop for 10 days.

•Then F1 progenies were isolated and phenotypes were

examined.

•The observed results are as follows:

P1 generation = 20 OK X 20 white eyefemale Male

P1 generation = 20 OK X 20 white eyefemale Male

Red eye female Red eye male White eyed male

No. of flies 11 6 5

F1 Generation Result

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

All white males were discarded

F2 selfing was carried out

RED EYED FEMALE

RED EYED MALE

WHITE EYED MALE

WHITE EYED FEMALE

No. of flies 37 18 20 16

F2 GENERATION RESULT

P3 generation = F2 OK X F2 ok X F2 white female Male female

F2 SELFING

RED EYED FEMALE

RED EYED MALE

WHITE EYED MALE

WHITE EYED FEMALE

No. of flies 55 24 21 20

F3 GENERATION RESULT

All white males were discarded

F3 selfing was carried out

P4 generation = F3 OK X F3 ok X F3 white female Male female

F3 SELFING

RED EYED FEMALE

RED EYED MALE

WHITE EYED MALE

WHITE EYED FEMALE

No. of flies 68 32 17 21

F4 GENERATION RESULT

DATE12 RED EYED FEMALE

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

TOTAL FLIES

Where as,

n= no. of white eyed male

N= total no. of progeny

GENE FREQUENCY

Gene frequency = n X 100N

CALCULATIONS

WHITE EYED MALE

TOTAL POPULATIONSIZE

FREQUENCY OF WHITE MALE

F1 5 22 22.72%

F2 20 91 21.97%

F3 21 120 17.5%

F4 17 138 12.31%

GENE FREQUENCY

CALCULATIONS…

0.00%

5.00%

10.00%

15.00%

20.00%

25.00%

F1 F2 F3 F4

GENE FREQUENCIES GRAPH

FREQUENCIES

0.00%

5.00%

10.00%

15.00%

20.00%

25.00%

F1 F2 F3 F4

GENE FREQUENCIES GRAPH

GENE FREQUENCIES

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.

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.

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. melanogastermay cause males to develop useful or detrimental traits, or may ultimately lead to the development of a new species.

INTERPRETATION …

• https://bu.digication.com/nahomiv/Sexual_Selection_and_Mating_Preferences_of_Female_

• http://www.ou.edu/journals/dis/DIS60/Ramachandra%20171.pdf

• www.googleimages.com

REFERENCE

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