5 Reproductive Isolation and Speciation

Question 1

what is a Species?

Answer 1

group of organisms sharing several features, which are capable of interbreeding and producing fertile offspring

Question 2

Speciation (5)

Answer 2

• the formation of a new species
• happens as a result of the isolation of parts of a population
• important factors in the process are reproductive isolation and the reduced gene flow between the different populations, which is a consequence of that isolation
• because the two isolated populations experience different conditions, different selection pressures act on them
• over a period of time both the genotype and phenotype of the isolated groups will change

Question 3

hybridisation (2)

Answer 3

• can be a cause for speciation, particularly in plants

- it is the production of offspring as a result of sexual reproduction between individuals from two different species

Question 4

geographical isolation (2)

Answer 4

• leads to reproductive isolation

- a physical barrier such as a river or a mountain range separates individuals from an original population

Question 5

Allopatric speciation (3)

Answer 5

• occurs when a population becomes physically or geographically separated and there can be no interbreeding or gene flow between the populations
• viewed as the main evolutionary process
• examples= when islands form, when rivers change course or when lakes dry up etc.

Question 6

Adaptive radiation (2)

Answer 6

• often after allopatric speciation

- occurs when one species develops rapidly to form several different species, which all fill different niches

Question 7

Population bottlenecks (5)

Answer 7

• when there is a disaster that wipes out majority of population and significantly decreases gene pool
• only a few individuals survive
• population will randomly lose a lot of variation, which means that a single mutation can have a bigger effect than usual
• after a while they will repopulate, but can become so different from original population genetically, that it becomes a new species
• so a big population will be back, but with more selected variants

Question 8

The Founder Effect (4)

Answer 8

• the loss of genetic variation when a small number of individuals leave the main population and set up a separate new population where they are geographically isolated
• they produce a voluntary population bottleneck
• any unusual genes in the founder members of the new population may become more frequent as the new population grows
• brings about a dramatic change in allele frequencies in a population

Question 9

compare and contrast population bottlenecks and the founder effect (2)

Answer 9

• both cause a limited gene pool, so the population has allele frequencies that are different from the original population
• a population bottleneck is imposed on a population by the loss of most members through natural events or human intervention, while the founder effect is the result of the isolation of a small group of organisms from the original population