Question

question 5 (multiple choice worth 4 points)
(05.02 mc)
which of the following is correct about mutations and genetic variation?

• it must be present in a population before natural selection can act upon the population.
• it arises in response to changes in the environment.
• it tends to be reduced when diploid organisms produce gametes and reproduce.
• it is created by the direct action of natural selection.

question 6 (multiple choice worth 4 points)
(05.02a mc)
each of the following answer choices compares a segment of dna from two related species that diverged from a common ancestor. assume a mutation rate of one mutation every 60 million years applies to all segments and that a mutation can happen only once at each position in a dna sequence. which pair of sequences shows that the two species diverged from their last common ancestor 60 million years ago?

• gattcact and aactcaca
• gcgcttat and acgtttgt
• tattcgcg and tattgccg
• tcacttaa and tcactcaa

Explanation:

Question 5

• For the first option: Natural selection acts on existing genetic variation (from mutations, etc.) in a population. So mutations (source of variation) must be present for natural selection to act.
• Second option: Mutations are random, not a response to environment (though environment can select for them).
• Third option: Meiosis (gamete production) and reproduction (like sexual reproduction) can increase genetic variation (e.g., crossing over, independent assortment), not reduce it.
• Fourth option: Natural selection acts on existing variation; it doesn't create mutations (mutations are random changes in DNA).

Step1: Understand the mutation rate

The mutation rate is 1 mutation every 60 million years, and a mutation can happen once per position. So, if two species diverged 60 million years ago, their DNA segments should have exactly 1 mutation (difference) between them.

Step2: Compare each pair of sequences

• GATTCACT and AACTCACA: Count the differences. Let's align:

G A T T C A C T
A A C T C A C A
Differences: G vs A, T vs A, T vs C, T vs T (no), C vs C (no), A vs A (no), C vs C (no), T vs A. That's more than 1.

• GCGCTTAT and ACGTTTGT: Align:

G C G C T T A T
A C G T T T G T
Differences: G vs A, C vs C (no), G vs G (no), C vs T, T vs T (no), T vs T (no), A vs G, T vs T (no). More than 1.

• TATTCGCG and TATTGCCG: Align:

T A T T C G C G
T A T T G C C G
Differences: C vs G, G vs C. That's 2 differences.

• TCACTTAA and TCACTCAA: Align:

T C A C T T A A
T C A C T C A A
Differences: T vs C (only 1 difference, at the 6th position: T vs C).

Answer:

It must be present in a population before natural selection can act upon the population.

Question 6