Download 7.1: Variations, Mutations, and Selective Advantage Learning Check:

7.1: Variations, Mutations, and Selective Advantage
The offspring of sexually reproducing organisms inherit a combination of genetic material (genes) from
both biological parents. The number of possible combinations of genes that offspring inherit from their
parents results in genetic variation among individuals within the population.
Variation: Difference betwee4n individuals, which may be structural, functional, or physiological.
Mutations: a permanent change in the genetic material of an organism; the only source of new genetic
variation.
Some mutations alter the identity of a particular nucleotide, while others remove or add nucleotides to
a gene. Mutations that occur in somatic cells can have significant effects on the individual, but will not
be passed on to the next generation. Mutation can be harmful, neutral, or beneficial to an organism.
Mutations that occur in gamete cells can be passed onto the next generation.
Mutations result in new alleles and therefore underlie all other mechanisms that produce variation, the
raw material for evolutionary change.
Selective Advantage: a genetic advantage that improves an organism’s chance of survival, usually in a
changing environment.
Organisms do not alter their genetic information so they can exist in new environments. When an
environment changes, some individuals in a population may have mutations that allow them to take
advantage of the change. They may survive and pass their beneficial genes onto their offspring.
Learning Check:
Eastern Massasauga Rattlesnakes are members of the Pygmy rattlesnake family, Sistrurus. They are
approximately 50 to 70 cm in length. Their bodies are brown, grey, or even black with 25 to 50 dark
blotches on their sides. Their bellies are dark grey or black and the underside of their chin is white. They
have a characteristic dark band that runs diagonally across their eyes to the back if their jaws. This band
is usually bordered by a lighter colour.
1. Identify the variations in the Eastern Massasauga rattlesnakes. [k/u]
The insecticide DDT was banned by many countries, including Canada, in the 1970’s. It is still used in
some parts of Africa, Asia, and South America.
An area infested with mosquitoes was sprayed weekly with DDT over several months. The graph shows
the mosquito count during spraying.
2. Why did some mosquitoes survive the first praying? [app]
a) More mosquitoes moved into the area.
b) The summer weather was cool and wet.
c) There was natural variation in the population.
d) Environmental factors changed as the summer progressed.
e) Most of the mosquitoes were old enough to reproduce.
3. Why did the DDT become less effective? [app, t/i]
a) Individual mosquitoes were able to change their gene in response to the
presences of DDT.
b) DDT caused mutations in the mosquitoes, which resulted in immunity.
c) The DDT reacted chemically with the mosquito’s DNA
d) The DDT was only sprayed once.
e) Mosquitoes that had a pre-adaptive resistance to DDT lived and passed their
beneficial genes onto their offspring.