Inheritance

Question 1

Many populations of insect pest have become resistant to insecticides. Explain how selection can result in an insect population which is resistant to insecticides?

Answer 1

Insecticide resistance already present in population
Resulting from mutation
Resistant insects are not killed by insecticide/survive
And are able to reproduce/breed
Passing on the relevant allele/gene to the next generation
Resulting in an increase in frequency of resistant allele in population

Question 2

Crop management preventing resistant moths increasing

Answer 2

Resistant moths are homozygous recessive
Moths from untreated fields survive
Crossing produces heterozygotes
Mom resistant are susceptible and die

Question 3

Explain why this programme would not work if the resistant allele were dominant

Answer 3

All heterozygotes would survive
And be able to breed
Pass on dominant allele
Increasing frequency

Question 4

Assumptions of HW equation

Answer 4

No selection 
Random mating
Large population 
No emigration 
No mutation 
Equally viable gametes 
Generations do not overlap

Question 5

Suggest reason why gene therapy for cystic fibrosis is not successful yet

Answer 5

Difficult to get DNA into sufficient cells/DNA may be inserted but not expressed
Body cells not at gamete/zygote stage
DNA only inserted into differentiated cells
Treatment must be repeated

Question 6

Suggest high incidence of Huntington’s disease in this population

Answer 6

Small founder population/common ancestor
Genetic isolation/small gene pool
No migration/inbreeding
High probability of mating with person with H allele
Reproduction occurs before symptoms are apparent
No survival/selective disadvantage

Question 7

Why Huntington disease has not been eliminated

Answer 7

Time interval of 1 month/too long
-Large no of mice born/die
- 12 hours is too short a time for mice to mix with population
Non seed years- no of mice is small

Question 8

How to measure allele frequency

Answer 8

Find frequency
Square root
Hw equation

Question 9

What is meant by directional selection

Answer 9

Variation in size is genetic 
Selection for/against an extreme 
For large mice/against small mice 
Only large survive and breed 
Leads to an increase in mean mass 
In cold conditions

Question 10

Geographical isolation

Answer 10

Populations separated by a physical barrier
No mixing of gene pools 
Different selection pressures
Become adapted to local environment 
Survive and reproduce 
Mutation in one group
Change in allele frequencies
Directional selection 
Isolated population/new species cannot interbreed

Question 11

Sex linked

Answer 11

Only seen in males/not females

Question 12

Caused by recessive alleles

Answer 12

Unaffected parent or mother

Question 13

Stabilising selection

Answer 13

Occurs in an unchanging environment
Initial range in values in which mean is best adapted
Selection against extremes
Mean/median/mode unaltered
Range/SD reduces
Repeated over many generations
Increasing proportions of populations become well adapted to environment

Question 14

Resistance to antibiotic becomes widespread

Answer 14

Frequent use of antibiotic kills bacteria/creates selection presses
Bacteria with mutation/resistance have selective advantage
Survive to reproduce more than other types
Pass on advantageous allele
Frequency of advantageous allele increases in future generations
Frequency of resistant types increases in subsequent generations

Question 15

Speciation

Answer 15

Isolated population/no gene flow/mixing of gene pools
Variation due to mutation
Some able to use new food
So less competition
Survive and reproduce to give new population

Question 16

The allele for nail patella is dominant

Answer 16

3 and 4 produce unaffected male so must carry recessive

But both affected by nail patella which must be dominant

Question 17

Gene is not sex linked

Answer 17

3 inherits X from mother, who is not affected, if sex linked, 3 would have nail patella on X chromosome and pass to female offspring, 10 is recessive female, so gene is not sexy linked

Question 18

How CN syndrome becomes common in closed community

Answer 18

Individuals with CN syndrome allele present in founder community
In closed community higher frequency of allele than in general population/ higher frequency of carriers
Greater chance of inbreeding
Greater chance of two recessive alleles coming together

Question 19

CN SYNDROME INCREASE IN FUTURE GENERATIONS

Answer 19

Individuals survive to reproduce
Greater chance of allele being passed on
Higher frequency of allele being passed on

Question 20

Reasons for low frequency of t allele found at carloforte

Answer 20

Mainland Italians didn’t bring allele
Hadn’t been exposed previously to malaria
Malaria less of a factor in Sardinia since calforte establishes
Insufficient time/generations for selection to operate

Question 21

Explain why observed ratios are not the same as expected ratios

Answer 21

Random fusion of gametes
Small sample size
Differential mortality(got to die sometime)- death rate

Question 22

During meiosis when the x and Y chromosomes pair up, they do not form a typical bivalent. Explain why?

Answer 22

X and Y chromosomes are different sizes/shapes
Chromatids unable to line up and form a bivalent
Short pairing region/most of length not homologous

Question 23

Discontinuous variation

Answer 23

As discrete groups