topic 6

Question 1

can evolution happen wo variation

Answer 1

NO

Question 2

key questions in evolution?

Answer 2

• Variation is universal
○ What maintains it
○ How variation is shaped by selections and other evolutionary factors

Question 3

what makes up our genetic code? stop and start codons?

Answer 3

• 4 bases, 20 amino acids
64 diff types of codon - represent 20 amino acids
start = ATG(methinonine)
stop = TAA,TAG,TGA

Question 4

two typed of codon changes

Answer 4

• Synonymous - silent- changes/mutations - do not alter amino acids
Nonsynonymous - replacement - changes alter amino acids

Question 5

how do genetic changes occur in pops? who came up w mutation

Answer 5

○ Proposed by dutch botanist Hugo de Vries in 1886
○ Observed plant species w new characters appearing that had no history in previous generations
○ From latin word mutatio - to change
• Necessary ingredient for change

Question 6

what are gene mutations? what do they lead to? when do they have evolutionary consequences?

Answer 6

Process of alteration of a gene or 
chromosome 
Product of the alteration 
	• Lead to New change in morphology, survivor, 
	behaviour, or some heritable traits 
Have evolutionary consequences only if 
they are transmitted to succeeding 
generations

Question 7

how do the nucleotides pair?

Answer 7

purine: A and G
pyrimidine: C and T
AT and CG
hydrogen bonds

Question 8

describe point mutations

Answer 8

Alterations of a single base pair
Change of a single nucleotide in a DNA template strand
can lead to the production of an abnormal protein

Question 9

two types of point mutations

Answer 9

• Base pair substitutions
— Replacement of one base pair by another at a specific DNA site in
a population or a species
• Frameshifts
— An insertion or deletion of base pairs in a DNA sequence that
alters the reading frame, resulting in multiple changes

Question 10

types of base pair mutations

Answer 10

• 
	• Transition 
		○ Substitution 
		○ A purine for a purine (a-g) 
		○ A pyrimidine for a pyrimidine (c-t)
		○ 
	• Transversions 
		○ Substitution 
		○ Purings for pyrimidines or vice versa 
		○ A or G - C or T 
		○ Eight possibilities

Question 11

look at diagram of transitions vs transversions. which is more common? why ?

Answer 11

Transitions are more common than transversions because
DNA repair enzymes can recognize wrong insertion representing a
a transition better than a transversion

Question 12

how do frame shift mutations work

Answer 12

• Alteration of reading frame = many changes downstream
  
  • Insertions and deletions (indels)

Question 13

describe indels

Answer 13

A single base pair or many 
Triplet reading frame shifted by 
one nucleotide or more-> 
downstream triplets are read as 
different codons -> different 
amino acids 
frequent compared to base 
pair substitutions

Question 14

how does recombination lead to sequence changes. caused by?

Answer 14

• Typically based on precise alignment of
DNA sequences
• Intragenic recombination due to difference
in sequence at two or more base pairs
○ Generates new DNA sequences
Due to gene conversion

Question 15

what is gene conversion

Answer 15

When a damaged DNA strand of one
chromosome repaired by enzymes inserting
bases complementary to sequence on
undamaged homologue

Question 16

describe unequal cross over . look at diagram

Answer 16

• Imperfect alignment - unequal exchange btwn two homologous sequences or chromosomes
Results:
Tandem (identical) duplication on one recombination
product & a deletion on the other
Length of affected region may range from a single base
pair to a large block of loci

Question 17

sickle cell anaemia ex.

Answer 17

• A single base change in DNA results 
	in a change in one RNA codon, 
	causing production of abnormal 
	hemoglobin called HbS 
	• 

	• Enough to disrupt normal action of 
	02-carrying globular Hb mols & 
	hence, of the RBCs 
	• Painful episodes 
	• How does it happen? 
Change of a "T" to "A" results in 
making of valine instead of normal 
glutamic acid on ß-subunit of Hb 
protein

Question 18

why is sickle cell maintained?

Answer 18

Sickle Hb confers a survival advantage to
individuals living in malaria infested areas
—7% of people of African descent carry an
allele

Question 19

cysticfibrosis- how does it happwn?

Answer 19

mos \t common in NA, NEUR, SW AFR
appens bc mutations in gene encoding Na- channel protein Two frameshift mutations — one caused by a two-nucleotide insertion and
the other by a one-nucleotide deletion
Mutations predicted to shift the reading frame of the protein and to
introduce a terminal codon
> 500 other base pair substitutions in this gene
Doesn’t allow whole protein to develop - introduces a stop codon

Question 20

how high are mutation rates

Answer 20

• Generally speaking, low per locus 
		○ Species with larger 
		genomes tend to have 
		higher mutation rates per 
		base pair per generation 
		Doesn't hold for viruses; 
		○ mutation rates in RNA 
		viruses (AIDS, Ebola, 
		influenza) 1000's X higher 
Hence, favours for rapid 
evolution to evade host 
defenses

Typi y ranges
10-5 — 10-9

Question 21

implications of gene mutation rate bacteria vs humans

Answer 21

• Although slow per locus, summed over all genes - has considerable effect
In bacterial in general:
1 mutation/100 million genes/generation
ex. ecoli 10 mil new mutations/day
In humans, in a population of 500,000, there’re
more than 2 million new mutations
A small fraction could have a substantial effect

Question 22

describe somatic mutations

Answer 22

Occur in non-reproductive cells 
Cannot be passed on to offspring 
Do not matter for evolution 
Rarely noticed, except when there's health 
impact

Question 23

describe germline mutations

Answer 23

○ Mutations in reproductive cells such as eggs

and sperms

Question 24

Effects of germline - range of effects possible

Answer 24

No change in phenotype
Occurred in a stretch of DNA with no function
-Occurred in a protein-coding regions but had no effect on amino acid sequence
Small change in phenotype
Backward curl of cat’s ears: single
mutation

BIG change in phenotype
DDT resistance in insects
Could even be lethal

Question 25

what are control genes? when are mutations on them worse?

Answer 25

• A control gene regulates expression of other genes

* Bigger the “control” larger the “effect:

Question 26

homoeotic mutations (on control gene)

Answer 26

May alter 1 or more phenotypic characters
Body size, colouration, action of an enzyme
Effecting survival/reproduction & in turn, fitness
Homeotic genes regulate development of anatomical structures
e.g., mutations in Antennapedia gene complex cause legs to develop in
place of antenna

Question 27

limitations to mutationa?

Answer 27

• Majority of mutations alter pre-existing
traits
• Can alter developmental processes but NOT
developmental foundations
• Ex, Just because they need one, great apes
cannot be able to develop monkey’s tail!
• We are dictated by our phylogenetic
constraints!
• Mutations occur at random
○ Chance that a particular mutation will occur is
not influenced by whether the organism is in an
environment in which that mutation would be
advantageous