Populations

Question 1

Define species.

Answer 1

Group of similar organisms that can reproduce to give fertile offspring.

Question 2

Define population.

Answer 2

Group of organisms of same species living in particular area at a particular time - potential to interbreed.

Question 3

Define gene pool.

Answer 3

Complete range of alleles present in population.

Question 4

Define allele frequency.

Answer 4

How often an allele occurs in a population.

Question 5

What is the Hardy-Weinberg principal?

Answer 5

Predicts frequencies of allies in population won’t change between generations, only true in large population with no immigration, emigration, mutations or natural selection.
Calculates frequency of alleles, genotypes and phenotypes.

Question 6

Hardy-Weinberg equation.

Answer 6

p + q = 1

p - frequency of dominant allele
q - frequency of recessive allele

Total frequency of all possible alleles for characteristic is 1, so frequencies of individual alleles must ass up to 1.

Question 7

How do you calculate the frequency of of one genotype if you know the others?

Answer 7

p^2 + 2pq + q^2 = 1

p^2 - frequency of homo dom
2pq - frequency hetero
q^2 - frequency homo recess

Question 8

How does genetic variation occur?

Answer 8

Mutation (changed in DNA base sequence lead to production of new alleles), random fertilisation during sexual reproduction and during meiosis (crossing over and independent segregation of chromatids).
Differences in environment.

Question 9

Define evolution.

Answer 9

The frequency of an allele in a population changing over time.

Question 10

How does natural selection work?

Answer 10

Individuals vary due to alleles, predation, disease and selection pressures make survival a struggle but some are more adapted making different survival and reproduction levels in a population. Those more adapted are more likely to survive and thus repose ice, passing on their beneficial alleles that create their phenotype. Frequency of beneficial allele increases through generations.

Question 11

What is stabilising selection?

Answer 11

Individuals with alleles for characteristics towards the middle range are more likely to survive and reproduce.
Occurs n stable environments and reduces range of possible phenotypes.

Question 12

What is directional selection?

Answer 12

Individuals with alleles for an extreme phenotype are more likely to survive and reproduce.
Often a response to environmental change.

Question 13

What is disruptive selection?

Answer 13

Individuals with alleles for extreme phenotypes for either each end of range more likely to survive and reproduce.
Occurs when environment favours more than one phenotype.

Question 14

What is specification?

Answer 14

Development of a new species from an existing one, when populations of same species become reproductively isolated - allele frequency changes causing changes in phenotype meaning they can no longer interbreed to produce fertile offspring.

Question 15

What is allopatric speciation?

Answer 15

Physical barrier creates geological isolation.

Question 16

Sympatric speciation.

Answer 16

Isolation without physical barrier.

Question 17

Describe allopatric speciation.

Answer 17

Geographically isolated populations experience different conditions making them experience different selection pressures making different alleles beneficial, allele frequency will also change with different mutations and genetic drift.
Differences in gene pool causing changing phenotype frequency, eventually making them so different they cannot produce fertile offspring - reproductively isolated.

Question 18

Describe sympatric speciation.

Answer 18

Random mutations may occur in population preventing members from breeding with others - reproductively isolated.

Question 19

Describe the changes to allele and phenotype that cause reproductive isolation.

Answer 19

• Seasonal, population could develop different mating seasons and become sexually active at different times of year
• Mechanical, changes in genitalia
• Behavioural, develop different courtship rituals that aren’t attractive to main population

Question 20

What is genetic drift?

Answer 20

When chance dictates which individuals survive and reproduce, rather than environmental factors.

Has a greater effect on smaller populations where chance has a greater influence.

Question 21

Describe how genetic drift works.

Answer 21

Individuals in population show variation on genotype, by chance the allele for one genotype is passed on more often than others, increasing its frequency potentially causing reproductive isolation eventually.