Essay Plan for Question S-E 12B
The formation of new species.
1) Introduction
a) Definition of species.
b) Brief overview of the main processes involved – genetic variation
affecting the phenotype and the reproductive success of individuals
(=ability to survive and pass on allele to offspring), consequently affecting
the allele frequencies in future generations, selection and reproductive
isolation may give rise to new species over time.
2) Variation
a) Variation arising from environmental and genetic variation – brief
mention of gene expression (protein synthesis) influencing the phenotype.
3) Mutation
a) What is mutation? Mention gene mutations (substitutions and deletions)
during DNA replication & affects on polypeptide. Mutation during
reproduction is important as this source of variation is passed on to
offspring. Only source of new variation.
b) Possibly consider genetic engineering as a type of artificial mutation.
Remove gene from cell or manufacture gene, insert into a vector, insert the
vector into host cell and culture.
4) Reproduction
a) Mitosis - The formation of two diploid genetically identical cells from one
parent cell. Importance in asexual reproduction.
b) Meiosis - The formation of gametes showing genetic variation from parent
cell. Sources of variation in the offspring – crossing over, independent
assortment of homologous chromosomes and chromatids, & random
fusion of gametes in sexual reproduction.
5) Selection
a) Change in allele frequency – deviation from H-W equilibrium.
b) Types to include directional, stabilising and disruptive selection. Could
include examples to illustrate, e.g. sickle-cell anaemia, resistance to
pesticides and antibiotics.
6) Speciation
a) The importance of reproductive isolation (examples to illustrate) in
speciation.
b) Allopatric & sympatric speciation. Could include example, e.g. Darwin’s
finches.
6) Conclusion