Variation and Linkage

Question 1

What are the structural classes of mutation?

Answer 1

Mutations are spontaneous changes in the DNA.
1. Point mutations (SNP): mutation in which a single nucleotide (A, T, C, or
G) is altered. (LCT expression)
- Most common form of genetic variation; >35’000’000 in humans
- Typically bi-allelic, as probability of repeat mutation is small
- Most SNPs are neutral, i.e. they do not have a (measurable) phenotypic effect, but some have positive or negative effects
- SNPs are often used in genome-wide association studies (GWAS)
2. Indels
3. Structural mutations:
a. VNTRs: sequences in which a shorter or longer core sequence is
repeated a variable number of times (D4 dopamine receptors)
- Microsatellite: short core sequence, e.g. (CTA)n
- Minisatellite: core sequence >100 bp
VNTRs are often located in non-coding regions and the number of
repeats is highly variable, indicating neutral evolution
b. Inversions, Translocations, Duplications, Deletion, Insertions

Question 2

How related are chromosomal mutations to reproductive isolation?

Answer 2

Different numbers of chromosomes prevent the production of fertile hybrid offspring, due to problems with synaptic pairing during meiosis.

Question 3

What is the Hardy-Weinberg equilibrium? How are the conditions under which it can actually occur?

Answer 3

Hardy-Weinberg rule describes the equilibrium between allele and genotype frequencies:

p2+2pq+q2=1

Conditions:

1. Large population
2. Panmixis
3. No migration
4. No mutation
5. No selection

Question 4

What is linkage equilibrium? Linkage disequilibrium?

Answer 4

Loci that are located in close proximity on the chromosome are genetically linked due to genetic linkage, resulting in linkage disequilibrium.

Linkage equilibrium:

• The frequencies in which the alleles of two loci end up in the gametes are independent of each other
• The loci are on separate chromosomes
• High recombination rate between the two loci

Linkage disequilibrium:
- Higher frequency of specific allelic combinations in the gametes, whereas other combinations are underrepresented

Question 5

What is the role of linkage disequilibrium in genetic hitchhiking?

Answer 5

Explains persistent combinations of phenotypic traits