Week 4 Selection, Gene Flow and Mutation Flashcards Preview

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Flashcards in Week 4 Selection, Gene Flow and Mutation Deck (44)
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1


If an allele is dominant then the heterozygote has the same phenotype as the ...... for the dominant allele

If an allele is dominant then the heterozygote has the same phenotype as the homozygote for the dominant allele


2

If an allele is recessive then the heterozygote has the same phenotype as the ..... 

If an allele is recessive then the heterozygote has the same phenotype as the other homozygote


3

If A is dominant then the heterozygote has the same fitness as the ..... for that allele 

If A is dominant then the heterozygote has the same fitness as the homozygote for that allele 


4

If A is recessive then the heterozygote has the same fitness as the ......

If A is recessive then the heterozygote has the same fitness as the other homozygote 


5

What is additive fitness?

If A is dominant but the traits have “additive fitness” then the heterozygote has a fitness value that is intermediate between the two homozygoes


6

What is Directional Selection

one allele is favoured 

7

What is Disruptive Selection

extremes of a trait are
favoured 

8

What is Stabilizing Selection

variation is reduced 

9

What is Balancing Selection

multiple alleles are maintained in the population 

10

What is Fluctuating Selection

the direction of selection changes over time 

11

How can we explain the shape of this curve? 


Fitness point of view?

What does this mean for deleterious recessive allels? Examples of this?

When A is at high frequency B is rare, and therefore B is most often present in heterozygotes

There is nothing to differentiate fitness of AA from AB individuals, and so there is very little phenotypic variation for selection to operate on

It is difficult to eliminate deleterious recessive alleles from a population (Ellis-van Creveld syndrome)

12

How can we explain the shape of this curve? 
Fitness point of view?

What does this mean for dominant discorders compared to recessive ones? Examples of this?

Even when the A allele is at high frequency the B allele is always ‚Äòvisible‚Äô 

From a fitness point of view, selection is always acting to drive out B alleles 

Dominant disorders can be driven out of a population more easily than recessive disorders, and hence there are less of them around (marfan syndrome)

13

What is heterozygote advantage (overdominace)? 

14

What is the graph curve for heterozygote advantage?

15

Heterozygote advantage: 

How can we explain the shape of this curve? 

There is a balance of the selection for A and against A

16

What is an example of heterozygote advantage?

Sickle-cell anemia
The sickle-cell allele (HbS) is autosomal recessive; meaning only homozygotes are affected 

However, HbS also confers partial resistance to malaria, meaning in certain parts of the world the heterozygote has the highest fitness 

17

What is the graph curve for heterozygote advantage when taking into account fitness?

18

What is heterozygote disadvantage (underdominance)?

19

What is the graph curve for heterozygote disadvantage?

20

What is frequency dependent selection?

when the fitness of a genotype depends on the frequency of the genotype in the population 

21

Frequency dependent selection: A genotype is favoured when it is common or rare? 

rare

22

Frequency dependent selection: When the genotype is favoured, the frequency of
alleles which contribute to it increase or decrease?

Increase

23

Frequency Dependent Selection: As these alleles increase in frequency, the genotype
increases or decrease in frequency?

increase

24

Frequency Dependent Selection: The fitness of the genotype decreases as it becomes more common or rare?

common

25

Frequency Dependent Selection: The decrease in fitness causes the alleles which contribute to the genotype to increase or decrease?

decrease

26

What is gene flow?

the processes by which individuals genes (or alleles) move from one population to another

- Gene flow can be one-directional or multi-directional
- Movement of individuals does not necessarily imply movement of genes

27

In the absence of gene flow populations tend to become genetically .... from one another 

genetically differentiated from one another 

28

What is panmixia?

random mating

A panmictic population is one where all individuals are potential partners

29

What is barrier to gene flow?

30

What is differentiation ?

Mainly visible in neutral loci, which are evoluing under drift alone