Keystone Test Biology: Genetics and Evolution 4

Question 1

Which evidence most strongly supports the common ancestry of all living organisms?

Accepted Answer

Universal use of the same genetic code (DNA/RNA/protein)

Answer

The near-universal genetic code—where the same codons specify the same amino acids across all life—strongly indicates common ancestry.

Question 2

What is the difference between genotype and phenotype?

Accepted Answer

Genotype is the allele combination; phenotype is the expressed trait

Answer

Genotype is an organism's genetic makeup (alleles), while phenotype is the observable, expressed characteristic.

Question 3

During crossing over in meiosis, which structures physically exchange segments?

Accepted Answer

Non-sister chromatids of homologous chromosomes

Answer

Crossing over (recombination) occurs between non-sister chromatids of homologous chromosomes at chiasmata during prophase I.

Question 4

A population of beetles has 60% green (G) and 40% brown (g) alleles. A drought kills all brown beetles. This is an example of:

Accepted Answer

Directional selection

Answer

Directional selection shifts the population toward one phenotypic extreme (green) by eliminating individuals at the other extreme (brown).

Question 5

Which statement best describes the role of mutations in evolution?

Accepted Answer

Mutations are the ultimate source of new genetic variation

Answer

Mutations introduce new alleles into populations, providing the raw genetic variation upon which natural selection and other evolutionary forces act.

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