Biology, Eighth Edition (Raven)

Chapter 20: Genes Within Populations

Pre Test

For a trait to evolve by natural selection there must be: (p. 396)
A)variation among individuals.
B)a mechanism of inheritance.
C)fitness differences among individuals based on that trait.
D)a and b
E)all of the above
The Hardy-Weinberg principle states that the genotypes in the next generation will be in the proportions p2: 2pq:q2 (where p and q are the frequencies of two alleles in the population) after one generation of: (p. 398)
B)assortative mating.
C)random mating.
Genetic drift: (p. 401)
A)occurs in all populations.
B)has the greatest effect in small populations.
C)will reduce genetic variation in a population.
D)can lead to loss of alleles in isolated populations.
E)all of the above
An organism's fitness depends only on its survival: (p. 404)
A cline is a gradual change in the frequency of a trait over a geographical distance. For example a melanic form of an insect may replace the non-melanic form over a distance of several hundred kilometres. This is an example of the balance between: (p. 405 )
A)mutation and drift.
B)drift and selection.
C)drift and gene flow.
D)mutation and gene flow.
E)selection and gene flow.
The disease sickle-cell anaemia is maintained at relatively high frequencies in populations in Africa and Asia by: (p. 407)
A)heterozygote advantage.
B)a balance between mutation and selection.
C)a balance between drift and selection.
D)a balance between mutation and drift.
E)all of the above
Disruptive selection favors: (p.409)
A)intermediate phenotypes.
B)phenotypes only at one end of the range.
C)no phenotypes.
D)phenotypes at both ends of the range.
E)none of the above
Experimental studies of natural selection have shown that: (p.410)
A)selection occurs very slowly in natural populations.
B)it is impossible to demonstrate that selection occurs at all.
C)selection occurs more rapidly than Darwin thought possible.
D)other evolutionary factors are more important.
Increase (or decrease) in a trait by selection may not occur if: (p. 412)
A)there is no genetic variation in the population for the trait.
B)genes determining the trait have pleiotropic effects.
C)genes determining the trait interact with other genes.
D)all of the above
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