3.7 Genetics, populations, evolution and ecosystems

Question 1

What does autosomal linkage mean?

Answer 1

• Two alleles found on the same autosome
• They do not assort independently and are linked

Question 2

What does codominance mean?

Answer 2

• When both alleles are expressed in the phenotype at the same time

Question 3

What are the Hardy-Weinburg equations?
What does each stand for?

Answer 3

(alleles) p + q = 1
(phenotypes) p^2 + 2pq + q^2 = 1

Question 4

What are the causes of genetic variation?

Answer 4

• Mutations
• Meiosis (crossing-over, independent assortment)
• Random fertilisation of gametes

Question 5

What else can cause phenotypic variation, aside from genetics?

Answer 5

The environment

Question 6

Explain how natural selection occurs.

Answer 6

• Random mutations produce new alleles and variation within a population
• Allele could be beneficial under specific selection pressures, differential reproductive success
• Beneficial allele passed down to offspring over many generations, frequency of allele increases until the species evolves

Question 7

What can impact allele frequency in a population aside from natural selection?

Answer 7

• Genetic drift = random chance impacts which alleles get passed on, some alleles lost and some favoured (larger impact in smaller populations)
• Founder effect, genetic bottleneck

Question 8

What may disruptive selection cause?

Answer 8

Polymorphism (distinct phenotypes in a population) and then sympatric speciation

Question 9

What is the main difference between allopatric and sympatric speciation?

Answer 9

• Allopatric is caused by geographical isolation
• Sympatric caused by reproductive isolation

Question 10

Explain how sympatric specciation may occur.

Answer 10

• Random mutations occur, new alleles arise
• These new alleles cause reproductive isolation and no gene flow between the populations
• Alleles passed on to offspring
• Over many generations, allele frequency increases
• Two populations become different species, can no longer reproduce and produce fertile offspring

Question 11

Explain how allopatric speciation may occur.

Answer 11

• Two populations geographically isolated, no gene flow
• Random mutations in each population, new alleles produced that may be beneficial
• Populations experience different selection pressures in their different environments
• Differntial reproductive success for individuals in the two populations due to different beneficial allele
• Different alleles passed down to offspring over many generations, allele frequency increases in each population
• Until the two populations can no longer breed to produce fertile offspring, become seperate species

Question 12

Explain 4 different causes of sympatric speciation.

Answer 12

1. Mechanical variation = anatomical differences causing variation
2. Temeperal variation = different breeding seasons
3. Behavioural variation = mutations affecting courtship behaviours
4. Hybrid sterility = can’t produce viable gametes

Question 13

What is an ecosystem?

Answer 13

Interactions between all the living organisms within a community and the non-living components

Question 14

What is a community?

Answer 14

Interactions between populations of different species

Question 15

Give examples of abiotic and biotic factors.

Answer 15

Abiotic = temperature, light, pH, water
Biotic = predator-prey relationships, mating

Question 16

What is a population?

Answer 16

• Group of organisms of the same species occupying the same space at the same time
• Can possibly interbreed to produce fertile offspring

Question 17

How can you estimate the size of a population using the mark-release-recapture method?

Answer 17

• Capture sample of species
• Mark in a way which will not impact survival (for example make them more obious to predators)
• Release, allow them time to distribute evenly in population
• Recapture and count marked individuals
• Estimate population size:
  N = (n1 x n2)/ m2

Question 18

What assumptions are made when using the mark-release-recapture method to estimate popualtion size?

Answer 18

• No death between 1st and 2nd capture
• No migration in or out of population between 1st and 2nd capture
• Marked individuals are given enough time to evenly distribure throughout population before 2nd capture
• Marking has no impact on chances of survival

Question 19

How can you estimate population size using a quadrat?

Answer 19

• Use a map of the area and randomly select coordinates using a random number generator
• Place a quadrat at each coordinate, count the number of individuals
• Calculate the mean number of individuals from a large number of samples taken using the quadrat
• Multiply this number up to the size of the area

Question 20

What does a niche refer to?

Answer 20

The role of the individual in the habitat it lives in

Question 21

Why do species not occupy the same niche?

Answer 21

Competitive exclusion principle:
- Two species can’t survive if they occupy the same niche, one of them will outcompete the other
- There will always be slight differences that allow the other species to survive more (diet, mates etc)

Question 22

What is a habitat and microhabitat?

Answer 22

Habitat = where an organism lives, characterized by the abiotic/biotic conditions
Microhabitat = smaller unit of a habitat

Question 23

What is carrying capacity?

Answer 23

The maximum stable population size that an ecosystem can support.

Question 24

When does primary succession occur?

Answer 24

Newly formed hostile, arid land with no plants or organic material (soil)
(volcanic eruption, shifting sand dunes)

Question 25

When does secondary succession occur?

Answer 25

Newly formed land with some soil and organic material
(fire)

Question 26

Describe the processes that occur during primary succession.

Answer 26

• Pioneer species (lichen) colonises the area, well adpated to hostile conditions
• Individials in species die and decompose forming first organic matter and humus
• Environment becomes less hostile as humus grows, more habitable
• Larger species of plant able to grow, outcompeting pioneer species, humus grows
• Climax community reached

Question 27

What can prevent succession?

Answer 27

• Grazing animals
• Burning forests/shrubs

Question 28

What are 3 features of a climax community?

Answer 28

• Populations are stable around the climax community
• Abiotic factors are constant
• The community is constant, same species present