Ch. 16 Evolution of Populations

Page 393

A. Variation and Gene Pools

• 1. A Gene Pool is made up of all the genes (including alleles) that are in a population.

A. Variation and Gene Pools

• 2. The Relative Frequency of an allele is how many times it occurs in a gene pool.

B. Natural Selection on Polygenic Traits

• 1. Polygenic Traits are controlled by 2 or more genes. (Ex: Skin color or eye color)

B. Natural Selection on Polygenic Traits

• 2. There are 3 ways Natural Selection can affect the distribution of phenotypes.– 1. Directional Selection– 2. Stabilizing Selection– 3. Disruptive Selection

B. Natural Selection on Polygenic Traits

• 3. Directional Selection- Individuals at one end of the curve have a higher fitness than individuals at the middle or other end.

B. Natural Selection on Polygenic Traits

• 4. Stabilizing Selection- Individuals in the center of the curve have a higher fitness than either end of the curve.

B. Natural Selection on Polygenic Traits

• 5. Disruptive Selection- Individuals at the upper/lower ends of the curve have a higher fitness than the middle.

• 1. Fossil records show that the size of the black bears in Europe decreased during interglacial periods of the ice ages, but increased during each glacial period.

• 2. Babies of low weight lose heat more quickly and get ill from infectious disease more easily, whereas babies of large body weight are more difficult to deliver through the pelvis and do not survive. Infants of a more medium weight survive much more often. For the larger or smaller babies, the baby mortality rate is much higher.

• 3. Suppose there is a population of rabbits. The color of the rabbits is controlled by two incompletely dominant traits: black fur, represented by “B”, and white fur, represented by “b”.

• A rabbit in this population with a genotype of “BB” would have a phenotype of black fur, a genotype of “Bb” would have grey fur (a display of both black and white), and a genotype of “bb” would have white fur.

• If this population of rabbits occurred in an environment that had areas of black rocks as well as areas of white rocks, the rabbits with black fur would be able to hide from predators amongst the black rocks, and the rabbits with white fur likewise amongst the white rocks. The rabbits with grey fur, however, would stand out in all areas of the habitat, and would thereby suffer greater predation.

• 4. Another example is the beak size in a population of finches. Throughout the wet years, small seeds were more common and there was such a large supply of the small seeds that the finches rarely ate large seeds. During the dry years, none of the seeds were in great abundance, but the birds usually ate more large seeds. The change in diet of the finches affected the depth of the birds’ beaks in the future generations. Their beaks range from large and tough to small and smooth.

Part deux

C. Genetic Drift

• 1. In small populations, alleles can become more or less common simply by chance which is called genetic drift.

C. Genetic Drift

• 2. The Founder Effect is a type of genetic drift in which a small subgroup of a population migrates to a new location.

animation

D. Isolating Mechanisms

• 1. Speciation is the formation of a new species.

D. Isolating Mechanisms

• 2. Reproductive isolation occurs when members of 2 populations can not reproduce.

D. Isolating Mechanisms

• 3. Behavioral isolation occurs when two population have the ability to reproduce but have different courtship rituals or reproductive strategies.

D. Isolating Mechanisms

• 4. Temporal Isolation occurs when 2 or more species reproduce at different times.

Analyzing Data

• Page 408• 1. Hypothesis A:• Hypothesis B: • 2. Big Difference:• 3. Conclusion:• 4. Question: