AUSTRALIAN CURRICULUM ALIGNMENT
Natural selection results from differential survival and reproduction of individuals due to differences in phenotype. A key mechanism of evolution, this change in the heritable traits occurs in a population over generations. Within any population, genetic variation will exist due to mutations. Mutations are changes in the DNA sequence of an organism and can provide organisms with either an advantage or disadvantage. Mutations that disadvantage an individual may reduce their fitness, and therefore their ability to survive and reproduce. Lowered chances of organism survival and reproduction, means their genetic material, along with the mutations are less likely to be passed on to the next generation. Traits of this nature can be referred to as “selected against”. However, there is an abundance of mutations of advantageous “selected for” traits that provide organisms with survival and reproductive advantage. These traits have a greater chance of being passed on through reproduction and therefore drive evolution. Survival of a trait is not solely dependent on sexual selection, it is also heavily influenced by predators and pathogens or environmental conditions of temperature, radiation, chemistry, or moisture. In this investigation, students observe natural selection in action by performing a cross of White and Red-eyed Drosophila (fruit flies). Drosophila are the perfect organisms to study genetics due to their accessibility, short twelve day generation time and four chromosomes. Students begin their genetic study with male and females of two different eye colours and predict expected filial phenotype ratios with the given parental genotypes. Once students have made their predictions, they are tasked with setting up a genetic cross between red and White-eyed flies. Students then sort the offspring by eye colour and compare their ratio predictions with actual results; using the collected data as evidence to determine whether natural selection influenced the population. The increase in the number of Red-eyed flies observable over the generations serves as evidence of natural selection.
Preparing Morgues
Clearing Drosophila vials
Preparing Vials with Medium (1 week before investigation)
Sorting the Drosophila (1 week before investigation)
Preparing Workstations
METHOD - STUDENT ACTIVITYSetting up Genetic Cross (Week One)
Clearing vials of P Generation (Week Two)
Sorting and Counting Drosophila (Week Three)
Setting up Genetic Cross
Ask students to go through the motions of the procedure before actually performing transfers. This will ensure students feel confident conducting the procedure and will prevent nervous or tentative students from panicking or freezing when flies try to escape.
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