Inheritance Flashcards Preview

Ppqs > Inheritance > Flashcards

Flashcards in Inheritance Deck (23):

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



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



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