VL 1 The foundations of evolutionary genetics

Question 1

Define phenotype and genotype

Answer 1

Phenotype
the set of observable characteristics of an individual resulting from the interaction of its genotype with the environment

Genotype
is the combination of alleles at a genetic locus or the genetic constitution of an individual organism.

Question 2

What is an allele and a genetic locus and a gene?

Answer 2

An allele is a variant of a gene.

A genetic locus is a specific location on the genome. (can be a single or many basepairs)

Gene: a stretch of DNA coding for a protein or functional RNA

Question 3

Who is associated with the theory of evolution through natural selection and what did he lack understanding of?

Answer 3

Charles Darwin; he lacked understanding of the unit of inheritance. (DNA was not known)

Question 4

What did Gregor Mendel discover and with what organism?

Answer 4

Mendel discovered the basic principles of inheritance using peas.

Question 5

What is genetic drift?

Answer 5

Genetic drift is the random fluctuation of allele frequencies in a population., even in the absece of selection.

Question 6

What does the adaptive landscape concept illustrate?

Answer 6

It illustrates fitness peaks and valleys in evolutionary fitness.

A certain phenotype can have multiple fitness peaks, but it is difficult to cross the fitness valley in between the peaks.

Question 7

“The modern synthesis” (4 points)

Answer 7

Mendel und Darwin combined.
1. Evolution is a gradual process – at least relative to the generation time of the organism in question.
2. Understanding evolution requires population genetics thinking – that means mathematics in general and statistics specifically.
3. Natural selection is the dominant force in evolution – at least regarding phenotypic traits.
4. Evolution acts the same way on all evolutionary levels, no matter if we compare individuals within a population or from different species.

Question 8

What are the key points of the neutral theory of molecular evolution proposed by Mooto Kimura in 1983?

Answer 8

It argues that most genetic variation at the molecular level is selectively neutral, maintained by mutation and genetic drift.

1. Most segregating alleles (genetic variations within a population) are neutral and do not affect an organism’s fitness.
2. Deleterious mutations are harmful and are quickly removed from the population by natural selection.
3. Beneficial mutations are rare but can spread through the population by positive selection.
4. The rate at which a new mutation becomes fixed (substitution rate) in a population depends on the effective population size (𝑁e) and the mutation rate (𝜇).
   -> This means that the substitution rate is equal to the mutation rate (𝜇), regardless of the population size.

Formula:
2𝑁𝑒𝜇 × 1/(2𝑁𝑒) =𝜇

Question 9

Name genetic markers used to study genetic diversity

Answer 9

• Allozymes – variation on the protein level
• Microsatellites – short tandem repeats on the DNA level
• SNPs (single nucleotide polymorphisms)
• RADs (restriction-site associated DNA markers)
• DNA sequence analysis (“full re-sequencing”)

Question 10

How does the Wright-Fisher model explain allele frequency changes?

Answer 10

It shows that allele frequencies fluctuate due to genetic drift, even without selection.

Question 11

Summary Slide of Lecture 1

Answer 11

• Ultimately, heritable organismal variability is always based on the process of mutation.
• Reduced to its simplest form, evolution can be understood as changes in allele frequencies.
• Within a population, such changes are driven by selection and drift.
• Thus, understanding the genetic basis of evolution ideally requires full
  genome sequencing.
• This has become achievable due to progress in sequencing technology.
• To perform meaningful analyses, it is necessary to understand the theory and the mathematical principle behind the processes any analysis tries to reveal.