20.5 Evolution

Question 1

What does epistasis mean

Answer 1

When the expression of the alleles is masked by another allele

Question 2

What is the expected ratio for an epistatic gene when a recessive epistatic allele is involved, YYRR and yyrr are crossed?

Answer 2

9;3;4

Question 3

What is the expected ratio for an epistatic gene when a dominant epistatic allele is involved, and YYRR and yyrr are crossed?

Answer 3

12;3;1

Question 4

Whats evolution

Answer 4

The change in allele frequency

Question 5

Whats stabilising selection

Answer 5

When the alleles are more towards the middle of the range due to minimal change to the environment. It reduces the possible phenotypes

Question 6

Whats directional selection

Answer 6

When a change in the environment means that there is a shift in the allele frequency so that the members of the population in minority for allele frequency are more likely to survive

Question 7

Whats genetic drift

Answer 7

When a change in the environment means that there is a shift in the allele frequency so that the members of the population in minority for allele frequency are more likely to sruvive

Question 8

Whats the genetic bottleneck

Answer 8

An event which causes a big reduction in population so gene pool is reduced eg; a natural disaster

Question 9

Whats founders effect

Answer 9

When a few organisms start a new population so there’s only a small gene pool eg; the migration of a species

Question 10

What does the hardy Weinberg principle predict and what conditions are needed for it to be true

Answer 10

In a stable population with no disturbing factors the allele frequencies will remain constant from one generation to the next

A large population, no migration, no natural disasters, no mutations and no natural selection

Question 11

What do p and a equal in the hardy Weinberg equations
And what’s the equations for the frequency of an allele
And the equation for the frequency of the genotype

Answer 11

P is the frequency of the dominant allele and q is the frequency of the recessive allele

Allele ; p + q = 1

Genotype p^2 + 2pq +q^2 = 1

Question 12

What the gene pool

Answer 12

The sum total of all the genes within a population at any given time

Question 13

Whats allele frequency

Answer 13

The relative frequency of a particular allele in a population

Question 14

Factors affecting evolution

Answer 14

-mutation is necessary for the existence of different alleles in the first place and the formation of new alleles leads to genetic variation

• sexual selection leads to increase in frequency of alleles that code for characteristics which improve mating success
• gene flow movement of alleles between populations eg immigration

-genetic drift in small populations the appearance of a new allele will have a greater impact

• natural selection leads to an increase in the number of individuals that have characteristics that improve their chances of survival

Question 15

Whats disruptive selection (diversifying selection)

Answer 15

The extremes are selected for and the norm selected against

Question 16

What is the sizes of a population affected by

Answer 16

1. Density dependent factors eg. Competition communicable diseases
2. Density independent factors eg immigration.climate change natural disaster and human activities

Question 17

Why does genetic drift have a bigger effect in larger populations

Answer 17

As each individuals genetic contribution to the next generation is more influential as there’s a smaller gene pool so losing alleles/ a reduction in the gene pool can have a much greater effect on genetic diversity