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Question 1

Suggest how a small organism, which can lay up to 400 eggs that develop into adults within 1-2 weeks and has distinct characteristics between males and females, is useful for studying genetic crosses

Answer 1

> Large number of eggs = improves reliability / use statistical tests / representative / large sample size / reduces sampling error
Small size = easily kept / stored
Easy to identify females from males
Short generation time = results obtained quickly

Question 2

Suggest reasons for conserving woodlands

Answer 2

>Protecting habitats / niches
>Protecting endangered species maintains biodiversitt
>Reduces greenhouse effect
>Source of medicnes / chemicals / wood
>Reduces erosion / eutrophication

Question 3

Summarise the ways in which new species may arise

Answer 3

> Isolation - geographically or reproductively
Genetic variation
Natural selection
Time

Question 4

What are ecosystems described as?

Answer 4

Dynamic - constantly changing

Question 5

What are the conditions for the Hardy-Weinberg principle?

Answer 5

> Organisms = diploid + reproduce sexually
Alleles not sex-linked - distributed equally between both sexes
No emigration or immigration
No mutations
No natural selection
Large population
Random mating (all genotypes equally likely to mate) + no mating between individuals of different generations

Question 6

What are the other sources of genetic variation?

Answer 6

> Random fertilisation of gametes

>Fusion of gametes is a matter of chance, and independent of each other

Question 7

What are the two types of succession?

Answer 7

Primary succession and secondary succession

Question 8

What are the types of variation?

Answer 8

> Discontinuous - discrete groups, result due to genetic factors, represented by bar graphs
Continuous - polygenic with characteristics showing a range, result due to environmental factors, represented by normal distribution curves

Question 9

What assumptions are made when using the mark-release-recapture method?

Answer 9

> No significant population changes due to immigration / emigration
Marking hasn’t affected the individuals’ chances of survival
Marked animals have been given sufficient time to thoroughly mix with population
No significant population changes due to deaths / births

Question 10

What does the Hardy-Weinberg principle calculate?

Answer 10

> Allele frequency, using a mathematical model
p + q = 1.0
p2 + 2pq + q2 = 1.0
Where p = dominant, q = recessive, and pq = heterozygous

Question 11

What does the Hardy-Weinberg principle predict?

Answer 11

> Frequencies of alleles in a population don’t change from one generation to the next
Only reliable/true if certain conditions are met

Question 12

What is a genetic bottleneck?

Answer 12

> Large reduction in size of population due to environmental events (i.e. natural disasters)/human activities
Produces a smaller population with reduced genetic diversity
Can lead to speciation

Question 13

What is allopatric speciation?

Answer 13

> Geographical isolation due to physical barriers e.g. oceans, rivers
Separated populations experience different selection pressures due to different environmental conditions
Selection in favour of individuals with advantageous alleles
Leads to change in allele frequency over time

Question 14

What is genetic drift?

Answer 14

When chance, rather than environmental factors, results in a change in allele frequency

Question 15

What is meant by uniformly distributed?

Answer 15

Organisms are equally spread

Question 16

What is sympatric speciation?

Answer 16

> Population become reproductively islated without becoming geographically isolated
Variation may occur due to mutations within population
Allele frequency changes over time
Individuals unable to interbreed successfully + produce fertile offspring

Question 17

What is the ‘competitive exclusion principle’

Answer 17

> If two species were to occupy the same niche
One would outcompete the other
Impossible to coexist

Question 18

What is the difference between dihybrid and monohybrid?

Answer 18

> Mono -> inheritance of a single characteristic

>Di -> inheritance of two characteristics at the same time

Question 19

What is the difference between dominant and recessive?

Answer 19

> Dominant => allele is always expressed when at least one copy present
Recessive => allele is only expressed when two copies present

Question 20

What is the difference between heterozygous and homozoygous?

Answer 20

> Hetero => only one type of allele is carried

>Homo => two different alleles carried

Question 21

What is the expected phenotypic ratio of the offspring of homozygous recessive and homozygous dominant parents in a codominant cross?

Answer 21

>F1 = 100% heterozygous
>F2 = 1:2:1 (25% homozygous for each allele, 50% heterozygous for both alleles)

Question 22

What is the expected phenotypic ratio of the offspring of homozygous recessive and homozygous dominant parents in a dihybrid cross?

Answer 22

>F1 = 100% heterozygous
>F2 = 9:3:3:1 (DR:Dr:dR:dr)

Question 23

What is the expected phenotypic ratio of the offspring of homozygous recessive and homozygous dominant parents in a monohybrid cross?

Answer 23

>F1 = 100% heterozygous
>F2 = 3:1 (dominant:recessive)

Question 24

What is the primary source of genetic variation?

Answer 24

Gene mutation, i.e. a change to the sequence of DNA nucleotide bases, leading to production of new alleles

Question 25

What may be the result of reproductive separation?

Answer 25

> New species arise from existing species (speciation)

>When genetic differences => inability of members of the populations to interbreed + produce fertile offspring

Question 26

What may cause a change in allele frequency?

Answer 26

>Mate-selection
>Migration
>Natural selection
>Genetic drift - random change in allele frequency due to chance
>Mutation

Question 27

What may individuals within a population of a species show?

Answer 27

> A wide range of variation in phenotype

>Due to genetic and environmental factors

Question 28

What would be the expected phenotypic ratio of a dihybrid cross involving a dominant epistatic allele?

Answer 28

> At least one copy of dominant epistatic allele masks expression of other gene
Heterozygous x heterozygous = 12:3:1 (dd:dr:rr)

Question 29

What would be the expected phenotypic ratio of a dihybrid cross involving a recessive epistatic allele?

Answer 29

> Two copies of recessive allele masks expression of other gene
Heterozygous x heterozygous = 9:3:4 (dd:dr:rr)
Example: lack of melanin masks expression of pigment colour

Question 30

When are quadrats used for estimating the size of a population?

Answer 30

For slow-moving or non-motile organisms