Build conclusions from the strongest trend or comparison, support them with data, then qualify the claim where statistics, samples or experimental context limit confidence.
Malaria is a serious and often fatal disease that is transmitted by the mosquito Anopheles gambiae. One method of reducing the incidence of malaria is to control the numbers of these mosquitoes.
In mosquitoes, as in humans, males have an X chromosome and a Y chromosome, while females have two X chromosomes. Researchers investigated the possibility of producing genetically modified (GM), fertile male mosquitoes in which most of the sperm contained a Y chromosome and not an X chromosome.
They predicted that introducing these males into a population of A. gambiae could greatly reduce the number of females in each generation and therefore reduce the numbers of eggs laid.
The researchers modified the gene for I-Ppol, so that it produced a version of I-Ppol that was active only during meiosis in the males, and was not active in the zygote. They then tested the effect of introducing these GM males into a mosquito population.
- Several cages were set up. 50 adult male mosquitoes and 50 adult female mosquitoes without the I-Ppol gene were placed in each cage.
- 150 adult GM males were introduced into each cage. In half of the cages (A), these GM males had the normal gene for I-Ppol. In the rest of the cages (B), the GM males had the modified gene for I-Ppol.
- The mean number of adult female offspring per cage was determined over the next six generations.
Fig. 3.1 shows the results.
mean number of adult females
Fig. 3.1
Describe and suggest explanations for the differences between the mean numbers of adult females in the two sets of cages during the experiment.