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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
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
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
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…
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