Evolutionary Biology 12

Question 1

Wat Bill hamilton (evolutionary ecologist) say about genetic conflict within an individual

Answer 1

recognised that an organism does not necessarily stand united in starting towards adaptation - i.e. the genome does not necessarily share the same evolutionary optimism as the individual and different parts of the genome may be working against each other.

Question 2

can selection only occur on individuals

Answer 2

• No, it can also occur within individuals
• A multicellular organism is a hierarchy of replicating units, cell types, organelles and genes that code for them.
• all of these units satisfy the 3 conditions for natural selection + adaptive evolution

Question 3

What are the 3 conditions for natural selection + adaptive evolution

Answer 3

1) variation
2) reproduction
3) heredity

Question 4

An example of selection within an individual

Answer 4

E.g. genes in Y chromosome

• only represented by males
• for y chromosome females are a waste of time
• optimal sex allocation for y chromosomes is 100% male
• will select for genes that bias to male gender being more prolific
• Autosomes and genes on the X chromosome have different optima and are selected to oppose any adaptation of Y to bias allocation towards males

Question 5

can deleterious genes (to the individual) spread in a population

Answer 5

• yes , genes that drive towards their own optima may spread in a population despite negative effects on their carriers fitness
• Every organism consists of genetic elements with differing evolutionary optima

Question 6

Give a hypothetical example of two-level selection with genome conflict.

Answer 6

1) newly formed cell with 2 types of mitochondria (A and a)
2) mitochondira are distributed via segregation at cell division into daughter cells

Scenario 1) - Both mitochondria replicate at same rate and are fairly distributed (no selection)

Scenario 2) - Mitochondria replicate at different rates (A>a) , if “a” benefits the cell more then this is conflict. Selection favours “a” at the cell level but “A” at the mitochondrial level.

Scenario 3) Mitochondria replicate at same rate, but are distributed unequally to daughter cells. as in (S2) conflict arises if segregation favours the mitochondria which is not more beneficial to the cell.

Question 7

Example of two-level conflict

Answer 7

E.G. baker yeast “petite” mitochondrial mutations

-defective mitochondria have 
 metabollic problems + poor 
 growth
- "petite" mutations are often 
 large deletions = allow faster 
 replication of MT genome.
- Clear case of genome 
 conflict , mutation favoured 
 at MT level as rapid 
 replication but deleterious 
 towards the cell.

Question 8

what is the relationship between genome conflict and sex

Answer 8

• genome conflict arises less easily in asexual systems

- sex allows greater scope for genomic conflict

Question 9

What are selfish genes

Answer 9

• selfish genetic elements are
  transmitted at a higher rate
  than the rest of the genome
• Use segregation distortion/ segregation bias (break rules of Mendelian inheritance and are consistently over-represented in offspring)
• drive meiosis away from equality, producing >50% of gametes with the selfish gene (meiotic drive)

Question 10

Segregation distortion

Answer 10

a phenomenon that the observed genotypic frequencies of a locus fall outside the expected Mendelian segregation ratio.

Question 11

Meiotic drive

Answer 11

a type of intragenomic conflict, whereby one or more loci (selfish gene) within a genome will affect the meiotic process in such a way as to favour the transmission of one or more alleles over another.

Question 12

Example of selfish genes

Answer 12

E.G. sex ratio meiotic drive in Drosophila 
- sex chromosome ensures 
 that all sperm carry the 
 selfish genetic elements 
- SR males only produce X- 
 bearing sperm
- gene causes degeneration 
 of Y-bearing sperm. (all 
 offspring of an SR male will 
 be female) - but will carry SR 
 gene to subsequent 
 offspring 
- should result in female- 
 biased population however 
 SR males only produce 1/2 
 as many sperm so poor 
 competition.

Question 13

When does genetic conflict occur

Answer 13

when a trait is selected for at one level but against at another.

Question 14

at what levels can selection occur

Answer 14

can occur at multiple levels, as long as there is scope for variation, reproduction, and heredity.

• can theoretically occur at levels higher then individual organism

Question 15

What can rescue population under sex-linked meiotic drive from extinction E.G. Drosphila

Answer 15

Polyandry

• female multiple mating can reduce frequency of a sex-linked meiotic driver
• may provide wider explanation for existence of polyandry