Biology Option D 2 Flashcards
D. 2.1
Define allele frequency and gene pool
Allele frequency: The proportion of allele within a population.
Gene pool: The sum total of alleles present in a sexually reproducing population
D. 2.2
What does evolution involve?
Change in allele frequency in a population’s gene pool over a number of generations.
D. 2.3
Discuss the definition of the term species
A species is a population whose members have the potential to interbreed to produce fertile offspring.
Some issues with this definition are:
1) Certain organisms (e.g. bacteria) do not reproduce sexually
2) Some organisms are known only through fossil records which fundamentally limits the scientists to ascertain breeding capacity.
3) Physical impossibility within the same species to mate (different sized dogs)
D. 2.4
Describe three examples of barriers to gene pools
2 main reproductive isolation barriers:
1) prezygotic isolation - no offspring are produced
Examples:
a) temporal: mates at different times of the year
b) behavioral: different courtship patterns
c) mechanical: genital differences
2) postzygotic isolation - infertile offspring are produced
Examples:
a) Hybrid inviability: failed development of reproductive maturity
b) Hybrid infertility: fail to produce functional gametes
c) Hybrid breakdown: F1 hybrids are fertile but F2 genreation will fail to develop or be fertile.
D. 2.5
Explain how polyploidy can contribute to speciation
Polyploidy is a condition in which an organism has more than two complete sets of chromosomes for all somatic cells. It is far more common in plant species as they lack separate sexes and are capable of asexual reproduction. This may occur as a result of the failure of a meiotic cell to undergo cytokinesis. Consequently, gametes are diploid and resulting offspring are tetraploid. Tetraploid cannot mate with diploid organisms and this leads to speciation.
D. 2.6
Compare allopatric and sympatric speciation
Similarities:
1) both involve speciation via isolation of the genetic gene pool from existing species
2) Both occur when natural selection creates genetic divergence between the new and ancestral populations
Differences:
1. A: physical separation while S: reproductive and behavioral separation
2. A: different geographical areas, S: same geographical areas.
Examples
3. A: adaptive radiation of Galapagos finches, S: Polyploidy in wheat strains
D. 2.7
Outline the process of adaptive radiation
Adaptive radiation means a rapid evolutionary diversification of a single ancestral lineage. It occurs when members of a single species have different characteristics from different environmental pressures. Adaptive radiation ultimately leads to speciation which could be enhanced by reproductive isolation.
Example: Galapagos finches
D. 2.8
Compare convergent and divergent evolution
Similarities:
Both explain the presence of similar structures in different organisms
Differences:
1. C: different ancestor, D: common ancestor
2. C: converge to analogous structures, D: diverge to homologous structures
3. C: more similar over time, D: more different over time
4. C: species are genetically different, D: genetically closely related
5. Examples:
C: wings of birds and insects, D: pentadactyl limb
D. 2.9
Discuss ideas on the pace of evolution, including gradualism and punctuated equilibrium
Gradualism:
1) slow, continuous change over time
2) gradual mutations and variations cause this
3) fossil records of gradual change support this
4) Example: modern horse changing in size and foot structure with changing environment.
Punctuated equilibrium:
1) rapid change in short periods of time
2) caused by rapid environmental changes such as volcanic eruption or meteor impact
3) gaps in the fossil record support this theory
4) appearance of many new species after a mass extinction support this theory
D. 2.10
Describe one example of transient polymorphism
Polymorphism: The occurrence of two or more different phenotypes in the same species - this reflects the effects of more than one allele in the gene pool.
Transient polymorphism is polymorphism that happens gradually. This is due to strong environmental selective pressure that leads to the elimination of one allele.
Example: An example of this is industrial melanism. Industrial activities made trees to blacken and moths that are lighter died from predators. On the other hand, melanic moths camouflaged and survived to pass on their genes. This ultimately leads to slow increase in the population of melanic moths.
D. 2.11
Describe sickle cell anaemia as an example of balanced polymorphism
Sickle Cell
Polymorphism: The occurrence of two or more different phenotypes in the same species - this reflects the effects of more than one allele in the gene pool.
Balanced polymorphism: A situation when there are two alleles in a gene pool and the frequency of two alleles is not changing. This occurs when selective pressures promote the coexistence of the two alleles - leading to stabilising selection.
Example: An example of this is sickle cell anaemia. Heterozygotes have an advantage in malarial regions because they are fitter than either homozygote.
