Lecture 02: Variation

Question 1

Holotypes

Answer 1

It´s a single specimen/organism, used to describe a particular species.

Question 2

What causes genetic variation?

Answer 2

• Mutation
• Recombination
• Horizontal gene transfer

Without variation that can be inherited: no evolution

Question 3

Mutations- Point mutation

Answer 3

Point mutation
Nucleotide change at a single position in a DNA or RNA sequence

• Often errors that occur during DNA replication during cell division
• In Germ-line and somatic cells in animals
• are random with respect of their effect on fitness, but not equally probably
• Mutation rates in prokaryotes much faster than in eukaryotes, because of the mutator alleles as fast track to adaptive evolution in prokaryotes
  -> Mutators can increase adaptation in changing environments (different selection pressures, coevolutionary race with virus)
• Can be caused by (ionizing) radiation e.g. Offspring after Chernobyle accident

Question 4

Mutations- chromosom mutation

Answer 4

Mutations in which the structure of a chromosome is altered. They occur due to rare but regularly occurring chromosome breaks, in which structural rearrangements are possible. (Deletion, insertion, duplication, translocation…)

-example: Neo-sex chromosomes in Black muntjac (new sex chromosomes) (last 0.5 mill. years)

Question 5

Mutations- Polyploidization

Answer 5

Polypolidization describes the process of numerical multiplication of chromosomes. This can affect individual chromosomes or entire chromosome sets in some or all of an individual’s tissues.

example: Chromosome numbers in sturgeons (several polyploidizations, evolution towards diploidization)

Question 6

Müllers ratchet

Answer 6

Müllers ratchet: inevitable accumulation of detrimental mutations in natural populations of limited size, with moderately high to high mutation rates, in the absence of recombination.

=> Mutation is under selection:
-> in higher eukaryotes selection against mutation (proofreading polymerase cuts off mutations) (like skin protects from radiation)
-> in prokaryotes, bacteria, viruses and unicellular eukaryotes selection in favour of mutation for faster adaptation

zwangsläufige Akkumulation nachteiliger Mutationen in natürlichen Populationen begrenzter Größe, bei moderat hohen bis hohen Mutationsraten, in Abwesenheit von Rekombination.

Question 7

Recombination

Answer 7

1) sexual recombination

• Randomizes the combinations of alleles at 2 loci
• in meiosis

(Picture: Locus 1: oval
Locus 2: diamond
Allele 1: red (inherited from mother)
Allele 2: blue (inherited from father))

Gametes (sperm) in offspring:
* Not recombined
* Recombined: combines the allele inherited
from the mother in one locus with the allele
inherited from the father in another locus.

Example:
1) Hybridisation & recombination after secondary contact
(Atlantic sea sturgeon and European sturgeon)
2) Lack of recombination under parthenogenesis by Amazon mollies (Poecilia)

2) other types of recombination??

• repair mechanisms,mutation
  transposable elements etc.
• ?(unisexual reproduction by Bdelloidea (Rotifers)
  *only females known
  *no genetic exchange among lineages
  *genetic depletion
  *+/- identical offspring (occasional point mutations))

Genetic recombination is the exchange of genetic material between different organisms which leads to production of offspring with combinations of traits that differ from those found in either parent.

Question 8

Horizontal gene transfer

Answer 8

HGT/ lateral gene transfer s the non-sexual movement of genetic information between genomes.
- in microbes (e.g. Viruses)
- at the origin of eukaryotes