BIOL204 Cons Gen Session 3

Question 1

What is the Census Population Size = Nc

Answer 1

Nc = a head count, you are sure you’ve counted 100% of population without statistics

Question 2

What is the Effective population size = Ne, ?

Answer 2

the number of successful breeders, (strictly the number of individuals in a theoretically ideal population having the same magnitude of random genetic drift as the actual population). Number of breeding individual, this excludes juveniles and non breeding adults

Question 3

What factors are needed for a population to be genetically viable?

Answer 3

be large enough to avoid inbreeding

retain sufficient genetic diversity for adaptation in response to environmental change

be large enough to avoid accumulating new deleterious mutations

Question 4

What should Ne be in order to avoid serious inbreeding depression?

Answer 4

Ne >50 Ne= Effective population size

however it is species specific and there is no one answer, that’s what conservationists need to work out.

Question 5

What is the IUCN?

Answer 5

The International Union for Conservation of Nature

The “red list” presents a measure for endangerment

Uses Nc not Ne

Question 6

What is a population bottleneck?

what does their effect on genetic diversity depend on? (2)

Answer 6

A large and sudden reduction in the size of a population, often due to demographic stochasticity, causes or increases the strength of genetic drift.

• how large the pop was before
• the duration of the effect - if small pop for many generations the effects of drift will be extreme.

Question 7

How can heterozygote excess be detected in a population?

Answer 7

by using the Hardy-Weinberg model

Question 8

What is the relationship between strength of genetic drift and population size?

Answer 8

Strength of drift will be negligible on large populations & will go up the smaller the pop, so an inverse relationship.

Question 9

Ht         (  1   -   1    ) t
----    =  (         ----   )
H0        (      2Ne   )
In the above equation what do Ht, H0, Ne and t mean?
what does this calculate?

Answer 9

Ht = heterozygosity at time t 
H0 = heterozygosity at time 0
Ne = effective population size
t = time (in generations) 
it calculates the STRENGTH of genetic drift

Question 10

How can you estimate effective population? Ne

Answer 10

Genetic marker data make estimates possible: a number of different approaches can be used but these tend to work from the same principle of measuring changes in heterozygosity through time i.e. measuring the strength of genetic drift as the strength of drift has a predictable trend with Ne

Ne = (4NmNf)/(Nm + Nf)

Question 11

in a pop bottleneck what alleles are less likely to survive? and what alleles will there be less of after a recent bottleneck?

Answer 11

the least frequent alleles

rare alleles

Question 12

In a population bottleneck what will happen to allelic diversity and heterozygosity initially?

Answer 12

allelic diversity will decrease steadily
there will be higher than expected heterozygosity H0>He
This can be calculated by HW model