Inheritance Flashcards
Many populations of insect pest have become resistant to insecticides. Explain how selection can result in an insect population which is resistant to insecticides?
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
Crop management preventing resistant moths increasing
Resistant moths are homozygous recessive
Moths from untreated fields survive
Crossing produces heterozygotes
Mom resistant are susceptible and die
Explain why this programme would not work if the resistant allele were dominant
All heterozygotes would survive
And be able to breed
Pass on dominant allele
Increasing frequency
Assumptions of HW equation
No selection Random mating Large population No emigration No mutation Equally viable gametes Generations do not overlap
Suggest reason why gene therapy for cystic fibrosis is not successful yet
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
Suggest high incidence of Huntington’s disease in this population
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
Why Huntington disease has not been eliminated
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
How to measure allele frequency
Find frequency
Square root
Hw equation
What is meant by directional selection
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
Geographical isolation
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
Sex linked
Only seen in males/not females
Caused by recessive alleles
Unaffected parent or mother
Stabilising selection
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
Resistance to antibiotic becomes widespread
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
Speciation
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
The allele for nail patella is dominant
3 and 4 produce unaffected male so must carry recessive
But both affected by nail patella which must be dominant
Gene is not sex linked
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
How CN syndrome becomes common in closed community
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
CN SYNDROME INCREASE IN FUTURE GENERATIONS
Individuals survive to reproduce
Greater chance of allele being passed on
Higher frequency of allele being passed on
Reasons for low frequency of t allele found at carloforte
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
Explain why observed ratios are not the same as expected ratios
Random fusion of gametes Small sample size Differential mortality(got to die sometime)- death rate
During meiosis when the x and Y chromosomes pair up, they do not form a typical bivalent. Explain why?
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
Discontinuous variation
As discrete groups
