6.1.2 (g)

Question 1

Define speciation

How does speciation happen?

Answer 1

Speciation: Evolution of 2 different species from an existing one through evolution

How speciation happens

• If a population becomes split or isolated it can amount to different selective pressures on the groups
• Different mutations and genetic drift can lead to changes in the population’s genotype, causing the populations to become reproductively isolated​
  
  • When there is no gene flow (mixing of genes) between organisms
• If populations are reproductively isolated for several generations, the genetic differences will accumulate to a point where the populations cannot reproduce fertile offspring, 2 new species are formed

Question 2

What is allopatric speciation?

Answer 2

• Speciation that occurs as a result of geographical barriers between populations
• Members of populations may be isolated from one another by a geographical/physical barrier such as the sea, or mountains
  
  • They can no longer mix and/or reproduce
  • The environments the different groups will have different selection pressures expressing different phenotypes and physical adaptations
• Separation results in the founder effect and genetic drift enhancing differences between populations

Question 3

What is sympatric speciation?

Answer 3

Sympatric Speciation: the formation of 2 new species from one original species due to reproductive
isolation whilst occupying the same geographical location

Ways Sympatric Speciation Occurs

1. Temporal Variation
   
   • By chance there will be some genetic variation in a population of a species, leading to phenotypic changes e.g. some plants will flower faster than other
   • This leads to seasonal changes in behaviour
   • Over generations, the ones that grow slower won’t be able to reproduce with the organisms
     that flower slower, leading to speciation
2. Behavioural Variation
   
   • ​​Some insects and birds carry out courtship behaviours, attracting certain mates attracted to those rituals
   • This reduces the amount of breeding within a population due to the behavioural differences,
     over generations this can cause isolation
3. Gametic Variation
   
   • Some flowers don’t like to be pollinated by specific genetic traits
   • Some plants choose not to reproduce to particular genetics, over time the plant population becomes reproductively isolated due to genotypes that are too distinct

Question 4

What is artificial selection?

Answer 4

• The use of selective breeding to breed organisms displaying desirable characteristics

Process of Aritifical Selection/Selective Breeding

in an exam question if one of the 2 terms are in the question, mention the other in your answer

1. Cross breed organisms with desirable characteristics
2. Assess the success of the outcome
   
   • E.g. assess to find the organisms with the highest yield
3. Breed the best/selected organisms over many generations

Question 5

What effect does selective breeding have on genetic diversity?

Answer 5

• Organisms with desirable characteristics are selected to breed (they are closely related individuals, so the breeding is known as interbreeding)
• Over generations the frequency of the desired alleles increases and eventually speciation occurs

Question 6

What is an animal example of selective breeding?

Answer 6

• Milk yield in cows shows continuous variation
• Selection pressures
  
  • A female cow is selected for:
    
    • large volume of milk yield
    • quality of milk yield
    • correct udder shape for milking machinery
  • A male cow (bull) is selected for what female offspring they produce
• Once a suitable bull is selected, the sperm is stored and collected
• Through artificial insemination the sperm is delivered to females
• The offspring should then increase in milk yield over many generations

Question 7

What is a plant example of selective breeding?

Answer 7

• Modern bread wheat is the result of years of artificial selection
• Different breeding and chromosome mutations caused bread wheat to form

Question 8

What problems (in terms of genetic diversity) do interbreeding bring about?

Answer 8

• Interbreeding limits the gene pool lowering genetic diversity, reducing the chances of a population evolving and adapting to environmental selection pressures
• Genetic disorders usually require recessive alleles, interbred organisms are closely related and likely to have recessive alleles, so interbreeding increases the chances of genetic disorder
  
  • Reducing the ability of interbred organisms to survive and reproduce

Question 9

How and why can you maintain genetic resources?

Answer 9

It is important to conserve rare and wild breeds as they have unique alleles to survive in different environmental conditions

Gene banks such as seed banks can be kept as a genetic resource, they can increase genetic diversity

Question 10

What are the ethical considerations surrounding artificial selection?

Answer 10

• The issue with artificial selection is the altering of one characteristic with no consideration for the other characteristics of the organism
• Dogs have been domesticated over years and evolve from the same origin
• But, many breeds are susceptible to diseases or conditions due to continuous interbreeding
  
  • E.g. Labradors have congenital hip disorder
• Domesticated animals retain friendly characteristics but cannot survive in the wild
• Animals are bred for their looks, with no consideration of their health or survival
• Dogs bred with minimal fat and are lean, will not be sufficiently well insulated to survive in cold temperatures