4: Mutation, variation & genome organisation

Question 1

Describe Jean Baptiste de Lamarck’s theory of inheritance

Answer 1

→ First theory of inheritance
→ organs that are used most grow bigger and offspring inherit these characteristics
→ we now know this is incorrect, still important because it began the search for the mechanism for inheritance

Question 2

What are mutations?

Answer 2

Failure to replicate genetic info faithfully
Can affect whole chromosome/single genes
Can be spontaneous / induced
Can be harmful, neutral or beneficial
Are the source of all genetic variation
Are necessary for natural selection and evolution

Question 3

Give some causes of mutation

Answer 3

Induced → radiation, UV, X rays
Mutagen → any agent that increases the mutation rate
E.g Chernobyl = ‘natural lab’ for testing the effects of radiation on mutation rates

Question 4

Describe polyploidy in humans

Answer 4

if you had greater than 2 sets e.g dispermy
= 3 complete sets of chromosomes, 3n = 69
Happens in 1-3% of conceptions - always lethal

Question 5

Give some examples of chromosome variation

Answer 5

Polyploidy
Aneuploidy
Translocations
Deletions
Inversions

Question 6

What are the polyploidy rates like in plants, compared to humans?

Answer 6

much higher - common

Question 7

Define aneuploidy

Answer 7

→ when one set of chromosomes is incomplete
E.g a chromosome is missing, an extra chromosome is present

Question 8

Define nullisomy

Answer 8

both members of a pair are missing - lethal

Question 9

Define monosomy

Answer 9

one member of a pair is missing - lethal

Question 10

Define trisomy + example

Answer 10

one extra chromosome, usually lethal
e.g Trisomy 21 0 Down’s syndrome

Question 11

Define translocation

Answer 11

→ exchange of parts between nonhomologous chromosomes
Carriers are unaffected
Offspring can have the wrong no. of copies of each chromosome → usually lethal

Question 12

Define deletion mutations

Answer 12

Part of chromosome missing
Severity depends on size of missing region

Question 13

Describe a paracentric inversion mutation

Answer 13

→ doesn’t include centromere
Often no problems in meiosis - a balanced rearrangement

Question 14

Describe a pericentric inversion mutation

Answer 14

→ include a centromere (both sides of it)
- Causes unbalanced gametes in meiosis that carry deletions, insertions and either 0 or 2 centromeres

Question 15

What was Crick’s 2nd great discovery?

Answer 15

3 nucleotides - a codon
Every codon codes for 1 amino acid
An amino acid can be encoded by more than 1 codon = code is degenerate

Question 16

What % of the human genome encodes proteins?

Answer 16

1.5%

Question 17

describe substitution mutations in coding regions

Answer 17

Silent / synonymous
Replacement / nonsynonymous (if in 2nd position in a codon will always change amino acid)

Question 18

Describe insertion/deletion mutations in coding regions

Answer 18

(indels)
Results in a completely different (probably faulty) protein
Because all amino acids downstream are changed

Question 19

Give some examples of Phenotypic polymorphisms due to mutation in 1 nucleotide

Answer 19

Albinism → Tyrosinase

Sheep in outer hebrides, light/ dark wool → Tyrosinase related protein 1

Sickle cell anaemia → haemoglobin beta gene
GAA (Glutamic acid) changed to GTA (Valine)

Question 20

What are SNPs?

Answer 20

Single nucleotide polymorphisms
95% of the genome not involved in protein coding / expression
Variation in these parts is very useful

Question 21

Describe satellite DNA

Answer 21

(simple tandem repeats)
Simple motif of DNA
Prone to errors in replication = diff no.s of copies
Nearly always harmless
Widely used in (1990s, 2000s) in finding diseases, conservation genetics, evo genetics, agricultural improvement