lecture 13 - natural selection cont

Question 1

• Ex -kermode bear polymorphism

Answer 1

• Adaptation for salmon feeding - why was the white coat color fixed?
  
  • Researchers pretended to be bears by wearing white cloak vs black cloak to see how salmon interact
  • Salmon seemed to approach more when white cloak was on
  • Adaptation- the white coat was fixed even though it was recessive as it benefitted them for feeding

Question 2

what does mean fitness account for

Answer 2

○ Accounts for allele frequencies and relative fitness
○ Selection is occurring

Question 3

describe antibiotic resistance

Answer 3

• Bacteria mutates to resist antibiotics
  
  • Due to overuse of antibiotics
  • Humans have mutations that make antibiotics not work? Wrong!!! It is the bacteria that mutate

Question 4

types of natural selection

Answer 4

1. Selection against the recessive homozygote
   
   2. Selection against dominant alleles
2. Selection with codominant alleles

Question 5

selection against recessive homozygote?

Answer 5

• Selection coefficient (s)= the probability of not surviving and reproducing - the exact opposite of fitness
  ○ w+ s = 1
  ○ w= 1-s
  
  • This type of selection is common with a number of genetic disorders where having the two copies of a harmful recessive allele lowers an individual’s fitness
  • In extreme cases - ex. When the recessive allele is lethal - fitness = 0
  • Models of natural selection are best understood when using the selection coefficient

Question 6

• Selection against the recessive homozygote - not lethal

Answer 6

• wAA= 1
  
  • wAa= 1
  • Waa= 1-s

Question 7

can an allele be removed in one generation?

Answer 7

• It is possible for the dominant allele to be removed in one generation
  ○ This happens when the dominant allele is lethal - the only way that selection can remove an allele in a single generation
  ○ Very different from selection against recessive alleles
  ○ Shows us how important the selection coefficient is

Question 8

recessive allele removal?

Answer 8

Even when a recessive allele is lethal, it takes time to
remove it from the population.”
○ Bc of heterozygotes
* Possibility of the recessive allele increasing due to genetic drift and mutation
* Higher values of s can result in faster changes over time

Question 9

selection w co dom alleles?

Answer 9

• The heterozygotes will show the effect of both alleles
  
  • Ex. Blood groups
    Also known as intermediate fitness to the heterozygotes

Question 10

describe selection sweep

Answer 10

• Polymorphisms shown on a chromosome before and after selection
  
  • Ancestral alleles in grey
  • Derived non ancestral alleles show in blue
  • A new allele (red) is going to rise in frequency specifically if it is linked to other alleles on the chromosome
    Selective sweep refers to a process by which a new advantageous mutation eliminates or reduces variation in linked neutral sites as it increases in frequency in the population

Question 11

other types of selection to consider?

Answer 11

• Selection and mutation
  
  • Selection against a mutation
  • Selection and genetic drift
    Selection and inbreeding

Question 12

how is evolution a two step process

Answer 12

• When a mutation is beneficial, it is more likely to be passed on
  
  • When lethal, it still can be passed via heterozygotes
  • Evolution is a two-step process: first, random genetic mutations appear in a population
    Then, the environment screens the organisms that carry them

Question 13

when is a mutation selected for?

Answer 13

• • Selected for when beneficial for fitness

Question 14

• Selection against a mutation?

Answer 14

• Unfavorable mutation - selected against bc unable to survive or reproduce
  
  • It might seem reasonable to assume that because allele frequency decreases when there is selection against that allele, selection against a mutation will totally remove the mutation in a population
    ○ Actually, this does not occur. Instead, an equilibrium is reached between selection against the mutation (which removes the allele) and mutation (which adds the allele)