23.1 – 1
What did Mendel’s findings about
genetics add to Darwin’s theory of
evolution by natural selection?
23.1 – 1
Mendel showed that inheritance is
particulate, and subsequently it
was shown that this type of
inheritance can preserve the
variation on which natural
selection acts.
23.1 – 2
Suppose a population of organisms
with 500 gene loci is fixed at half of
these loci, and has two alleles at
each of the other loci. How many
alleles are found in the gene pool?
Explain.
23.1 – 2
750.
Half of the loci (250) are fixed,
meaning only one allele exists for
each locus: 250 x 1 = 250.
There are two alleles each for the
other loci: 250 x 2 = 500.
250 + 500 = 750.
23.1 – 3
Which parts of the Hardy-Weinberg
2
2
equation (p + 2pq + q = 1)
correspond to the frequency of
individuals that have at least one
PKU allele?
23.1 – 3
2pq + q2
2pq represents heterozygotes
with one PKU allele and q2
represents homozygotes with two
PKU alleles.
23.2 – 1
Of all the mutations that occur, why
do only a small fraction become
widespread in a gene pool?
23.2 – 1
Most mutations occur in somatic cells
that do not produce gametes and so are
lost when the organism dies. Of
mutations that do occur in cell lines that
produce gametes, many do not have a
phenotypic effect on which natural
selection can act. Others have a harmful
effect and are thus unlikely to spread in
a population from generation to
generation because they decrease the
reproductive success of their bearers.
23.2 – 2
How does sexual recombination
produce variation?
23.2 – 2
A population contains a vast
number of possible mating
combinations, and fertilization
brings together the gametes of
individuals with different genetic
backgrounds. Sexual
reproduction reshuffles alleles
into fresh combinations every
generation.
23.3 – 1
In what sense is evolution more
“predictable” than genetic drift?
23.3 – 1
Natural selection is more
“predictable” in that it tends to
increase or decrease the frequency
of alleles that correspond to
variations that increase or decrease
an organism’s reproductive success in
its environment. Alleles subject to
genetic drift all have the same
likelihood of increasing or decreasing
frequency.
23.3 – 2
Distinguish genetic drift and gene
flow in terms of (a) how they occur
and (b) their implications for future
genetic variation in a population.
23.3 – 2
Genetic drift results from chance
fluctuations of allele frequencies
from generation to generation; it
tends to decrease variation over
time. Gene flow is the exchange of
alleles between populations; it tends
to increase variation within a
population but decrease allele
frequency differences between
populations.
23.4 – 1
Does nucleotide variability in a
population always correspond to the
phenotypic polymorphism? Why or
why not?
23.4 – 1
No.
Many nucleotides are in noncoding
portions of DNA or in
pseudogenes that have been
inactivated by mutations. A
change in a nucleotide may not
even change the amino acid
encoded because of the
redundancy of the genetic code.
23.4 – 2
What is the relative fitness of a
sterile mule? Explain.
23.4 – 2
Zero, because fitness includes
reproductive contribution to the
next generation, and a sterile
mule cannot produce offspring.
23.4 – 3
Explain what is meant by the
“reproductive handicap” of sex.
23.4 – 3
Only half of the members (the
females) of a sexual population
actually produce offspring, while
all the members of an asexual
population can produce offspring.