Quiz 3 Genetics & Natural Selections

A  A mutation causing brushes to develop a stem and grow into trees, affects the fitness of the original gene-pool by shading all those individuals that lack the mutation and remain low brushes. With increasing population densities (higher frequency) of the tree genotype in subsequent generations, the brushes are eventually replaced.

B  Frequency dependent selection explains why bacteria are able to develop antibiotic resistance, and elephants are changing much slower (generation turnover time).

C  Darwin’s giraffe example is now understood to only hold true for intermediate frequencies of giraffes. In dense giraffe populations there is no selection for longer necks, because they trample the trees.

A  Because Malaria is caused by the sickle cell anemia as long as mosquitoes are around. In areas where mosquitoes can’t survive, sickle cell anemia cannot be transmitted.

B  Because the S allele is reintroduced into the human gene pool by mosquitoes that have been encapsulated in amber and preserve the sickle cell anemia genes.

C  Because there is an “overdominance” of the heterozygote SA carriers in central Africa where Malaria is common. It means in that area the heterozygote has better fitness than either homozygotes AA and SS (outside that area though it is better to be an unaffected homozygote AA).

A  Heterozygotes are always selected for at a lower rate than homozygotes, no matter whether they carry a dominant allele or not.

B  The heterozygote containing the dominant allele is not increasing in allele frequency because of over-balancing.

C  The heterozygote containing a dominant allele that increases fitness, is selected for and the A2 allele frequency increases quicker through subsequent generations than if it wasn’t dominant.

A  That situation describes a genetic drift.

B  The allelle may become so frequent in the population over subsequent generations, that it replaces other alleles (genetic sweep).

C  The frequency containing the mutated allele becomes less frequent.

A  The genotype A2A2 should eventually increase in frequency.

B  The genotype A2A2 should eventually decrease in frequency.

C  Even though A2A2 provides a fitness advantage, Hardy-Weinberg equilibrium prevents an increase of allele frequency.

A  Positive selection is what nature does, negative selection is artificial (human) selection.

B  Positive selection leaves allele frequency unaffected, while negative selaction increases allele frequencies.

C  When a given allele has higher fitness than another, then natural selection will increase its frequency in the population.

A  “Grand” chromosome mutations do not exist, because they would not have allowed life on earth to develop.

B  A structural mutation.

C  Point mutations, named after the pointy appearance of chromosomes after mutating.

A  The coding system risks that any mutation will result in a serious disorder (deletrious mutations).

B  A point mutation of one base can be non-synonymous and result in a different amino acid being used, or in a synonymous (slient) change for a codon that results in the same amino acid.

C  The coding system makes sure that no point mutation can occur (polymorphic equilibrium).

A  Isolation and drift prevent the formation of new species.

B  Overdominance is the strongest force for genetic mixing (balanced polymorphism).

C  Segregation where chromosomes are distributed to offspring, and Recombination where chromosomes break and interchange segments.

A  That the population will go extinct soon.

B  A deviation from HW equilibrium reveals differential survival of genotypes and thus natural selection.

C  It indicates genetic drift.