7B

Question 1

What is the Hardy-Weinberg principle?

Answer 1

It is a mathematical model that predicts the frequencies of alleles in a population - given the conditions won’t change from one generation to the next:

• No mutations, no births or deaths, no Immigration or Emigration or natural selection
• Random mating

Question 2

The Hardy-Weinberg can also test…?

Answer 2

Whether selection or any other factors are influencing allele frequencies. if the frequencies do change between generations in a large population then there’s an influence of some kind

Question 3

The Hardy-Weinberg equation for the total genotype frequency of a population

Answer 3

p2 + 2pq + q2 = 1
p2 = frequency of homozygous dominant
2pq = frequency of heterozygous
q2 = frequency of homozygous recessive

Question 4

The Hardy-Weinberg Formula for a single allele frequency

Answer 4

p + q = 1

If the Dominant allele frequency is 0.4, the recessive allele frequency must be 0.6, as 0.4 + 0.6 = 1

Question 5

What is Variation?

Answer 5

The differences between individuals. Variation within a species is called intraspecific variation

Question 6

What is Evolution?

Answer 6

The frequency of an allele in a population changes over time. It can occur by genetic drift or by natural selection

Question 7

Types of Natural Selection

Answer 7

Stabilising Selection
Disruptive Selection
Directional Selection

Question 8

What is Stabilising Selection?

Answer 8

Individuals with alleles for characteristics towards the middle of the range are more likely to survive and reproduce. It occurs when the environment isn’t changing and reduces the possible range of phenotypes.

Question 9

What is Directional Selection?

Answer 9

Individuals with alleles for a single extreme phenotype are more likely to survive and reproduce. This can be a response to environmental changes.

Question 10

What is Disruptive Selection?

Answer 10

Individuals with alleles for extreme phenotypes are more likely to survive and reproduce, however it is the opposite to Stabilising Selection as the middle range is lost (Favours more than one phenotype, E.g. small fish and large fish survive, whereas middle size fish are too big to hide from predators and eaten by the bigger fish)

Question 11

What is Speciation?

Answer 11

Speciation is the development of a new species from an existing species. It occurs when populations of the same species become reproductively isolated, which changes allele frequencies, causing a change in their phenotype, eventually the new population cannot interbreed with the old population - they’ll become reproductively isolated - separate species

Question 12

What is Geographical Isolation?

Answer 12

When physical barriers, E.g. floods, earthquakes, volcanos, etc. divides the population. Therefore there is no Gene Flow (transfer of genes) between the two populations, which can lead to Allopathic speciation

Question 13

What is Allopathic Speciation?

Answer 13

Populations that are geographically isolated will experience different environmental conditions, experiencing different selection pressures, changing the allele frequency

Question 14

Allopathic speciation, and its different allele changes

Answer 14

• Different alleles will become more advantageous in the other population, so natural selection occurs
• With different allele frequencies, mutations will occur independently in each population
• Genetic drift

Question 15

What is Sympatric Speciation?

Answer 15

It occurs when random mutations within a population prevent individuals from breeding with other members of that population that don’t carry that mutation

Question 16

Mechanisms of Reproductive Isolation

Answer 16

• Seasonal changes - different mating/flowering seasons
• Mechanical changes - changes in shape, size or function of genitals can prevent successful mating
• Behavioural changes - different courtship behaviour

Question 17

Evolution via Genetic Drift (also known as random shift)

Answer 17

By chance, an allele is inherited and expressed more than another allele, therefore the number of individuals with the allele increases. By chance, the same allele is passed down generations, which can lead to evolution as the allele becomes more popular in the population

Question 18

Genetic drift, Natural Selection and Genetic Drift on Population size

Answer 18

Evolution via genetic drift usually has a greater effect in smaller population sizes where chance has a bigger influence. Whereas in larger populations, any chance factors tend to even out across the whole population

Question 19

Speciation and Diversity

Answer 19

the diversity of life on earth today is a result of speciation and evolutionary changes over millions of years - started with one species, which is split into another species, which is split into multiple species, Etc.