Topic 1 Evolution: Sources of Variation

Question 1

• New alleles could be introduced to the population with genetic mutations.

Answer 1

Mutation

Question 2

• Genetic recombination such as crossing over, independent assortment, and random joining of gametes can occur during sexual reproduction.

Answer 2

Sexual Reproduction

Question 3

• Diploid organisms have two copies of each chromosome. In heterozygous conditions, the recessive allele is stored for later generations, and thus more variations are maintained in the gene pool.

Answer 3

Diploidy

Question 4

• Mating with unrelated partners results in mixing of different alleles and creating new allele combinations.

Answer 4

Outbreeding

Question 5

• The maintenance of different phenotypes in a population. One phenotype is usually the best and thus has increased allele frequency. However, polymorphisms, the coexistence of two or more different phenotypes, can exist and be maintained:

Answer 5

Balanced Polymorphism

Question 6

• When a heterozygote condition bears greater advantage than either homozygous conditions. For example, sickle cell anemia is a recessive trait, but being heterozygous for the trait confers resistance against malaria.

Answer 6

1. Heterozygote advantage

Question 7

• The superior quality of offspring resulting from crosses between two different inbred strains, species, or varieties of organisms. Hybrid superior quality results from reducing deleterious recessive homozygous conditions and increasing heterozygous advantage.

Answer 7

2. Hybrid Vigor (heterosis)

Question 8

• Occurs when least common phenotypes have a selective advantage. Common phenotypes are selected against. Rare phenotypes will increase in frequency and will then be selected against, repeating the cycle. For example, predators use search images of common phenotypes to find prey, allowing prey with rare phenotypes to escape. The rare prey phenotype eventually becomes common, and then the cycle repeats.

Answer 8

3. Frequency-dependent selection (minority advantage)

Question 9

• These are variations that are passed down without any selective value, such as fingerprints in humans.

Answer 9

Neutral Variation

Question 10

• Variation of a species is dependent on climate or geographic conditions. A graded variation of a phenotype due to this is known as a cline. Variation from north to south environments is a north-south cline.

Answer 10

Geographic Variation