This aesthetic, in-depth, neatly typed document summarises 4.3 of strand 4 (Evolution) of the IEB grade 12 mind action series textbook: Formation of new species. It includes the full 4.3 Formation of new species syllabus as well as additional class notes, own research notes and all relevant diagram...
Species: Group of organisms that closely resemble each other and are able to interbreed
Causes of variation in a species:
• Sexual reproduction:
- Meiosis: Random arrangement of homologous chromosomes on equator, & crossing over when
bivalents from
- Chance fertilisation: Random combination of male and female gametes
- random mating: Every female gamete has equal chance to be fertilised by every male gamete
• Mutations:
- Changes in base sequences of DNA
- Deletion or duplication of whole chromosome
Variation in populations due to mutations:
- Di erent beak forms of Galapagos nches
- Colour of white lions caused by recessive trait derived from harmless mutation
- Resistance of bacteria to antibiotics
E ects of inbreeding and outbreeding:
• Inbreeding:
- Leads to loss of genetic diversity (prevents evolution)
- Results in homozygosity (more chance of recessive/harmful traits) = inbreeding depression:
Animals have lower birth weight and plants produce less seeds
• Outbreeding:
- Leads to increase of genetic variation (increase evolution)
- Promotes heterozygosity
, - New/desirable traits introduced into population
• Human inbreeding is frowned upon because:
- Close relatives carry same mutation for recessive disease
- Increases chances of o spring receiving harmful allele
- Risk of genetic disease
~ Common ancestor: 1 in 20 chance of disease
~ First cousin: 1 in 11 chance of disease
~ First degree relative: 1 in 2
(The closer the relationship, the greater the risk of genetic disease)
Example of outbreeding in plants:
• Brassica family: Wild mustard plant species with di erent traits
• Breeding with plants with di erent traits = variety of di erent vegetables (Kohlrabi, kale, broccoli,
brussels sprouts, cabbage, cauli ower)
Founder e ect:
Loss of genetic variation when small number of individuals from a larger population establish a new
colony (due to migration or geographic isolation)
• Gene pool of new population is di erent and hence form new population di erent to parent
population (eventually become a new species)
• eg. South African Cheetah - low genetic diversity due to founder population surviving major
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