Variation and Mutation

Question 1

where does variation come from? (3)

Answer 1

environmental variation: individuals can possess diff phenotypes as result of exposure to diff env, despite identical genotypes

genetic variation: individuals can possess diff phenotypes as result of diff genotypes, transmitted from parents to offspring

genotype by environment interaction: individuals can possess diff phenotypes as a result of interaction of genotypes w environment

Question 2

phenotypic plasticity

Answer 2

genetically identical individuals can have diff phenotypes in diff environmental conditions

Question 3

reaction norm

Answer 3

pattern or range of phenotypes that same genotype can possess as result of diff environment

Question 4

mutation

Answer 4

• ultimate source of genetic variability
• a change in DNA base sequence
• discovered by T.H. Morgan (fruit flies)
• generally classed single gene mutations OR chromosomal mutations (which affect many genes)
• initially, new mutation at diploid locus is 1/(2N), where N = pop size

Question 5

mutagens

Answer 5

can cause mutations

Question 6

DNA structure

Answer 6

G-C (3 H bonds)
A-T (2 H bonds)

phosphodiester linkage
sugar-phosphate backbone

Question 7

flow of genetic info

Answer 7

DNA -> mRNA -> protein

transcription translation

64 possible codons, 20 possible AAs

Question 8

stop codon

Answer 8

UAA/UGA/UAG

Question 9

start codon

Answer 9

AUG (methionine)

Question 10

DNA mutation

Answer 10

due to DNA alteration
due to DNA copying error (most common in repeating sequences)

Question 11

point mutations

Answer 11

• single base pair changes
• results in new alleles
• transitions more common than transversions

Question 12

transition and transversion

Answer 12

transition - purine to purine or pyrimidine to pyrimidine
transversion - purine to pyrimidine or vice versa

Question 13

3 potential impacts (point mutation)

Answer 13

(1) synonymous (silent) mutations - no change in AA
(2) non-synonymous mutations - change in AA
(3) non sense mutations - premature stop (often produces non-functional proteins)

Question 14

insertions or deletions

Answer 14

• like point mutations, can vary in effect
• any non-multiple of 3 (insertion/deletion) will shift codon reading frame

Question 15

fitness impacts of mutation

Answer 15

mutation may result in phenotypic changes
- neutral - no impact
- deleterious (disease-causing) - reduces individual fitness
- beneficial - increases individual fitness
- lethal - organism death before reproduction

Question 16

sickle cell anemia

Answer 16

• deleterious allele persistent in pop
• homozygous mutant allele: sickle-cell anemia
• homozygous normal allele: susceptible to malaria
• heterozygous: resistance to malaria (heterozygote superiority maintains mutant allele)

Question 17

where do new genes come from?

Answer 17

gene duplication via 2 mechanisms:
(1) duplication by unequal crossing over (meiosis)
- homologous chromosomes align incorrectly
- inner chromatids cross over at non-allelic repeat loci
(2) duplication by retroposition
- introns spliced out (processed mRNA) -> reverse transcription
- this copy can be inserted into genome (same exons, no introns => new gene); often non-functional

Question 17

exon/intron

Answer 17

exon - coding region
intron - non-coding region

Question 18

pseudogene

Answer 18

non-functional; no regulatory sequences for transcription to RNA

Question 19

comparison of unequal crossing over and retroposition

Answer 19

unequal crossing over - genes have same introns as original genes, typically occur in tandem with original genes on same chromosome

retroposition - genes typically lack introns, may be found far from original gene

Question 20

DNA derived from scratch

Answer 20

derived from non-coding regions of DNA (e.g. removed stop codon)

Question 21

chromosome mutations

Answer 21

may affect only gene order and organization and/r produce duplication or deletions that affect large amount of genetic material

Question 22

chromosome mutations types (2)

Answer 22

inversions (loop over, breaks, reanneal)
- drosophila: suggests due to linkage, higher fitness for certain inversions
- genes closer together on chromosomes are closer linked

polyploidy
- diploid gametes
- 1st gen can self-fertilize, mate w 4n sibling, or backcross w parent
- tetraploid 2nd gen individuals

Question 23

mutation rates & natural selection

Answer 23

• the rate at which mutations occur subject to natural selection
• heritable variation exists in accuracy of enzymes that synthesize and repair DNA
• there is variation in fitness among variants in particular environments
• individuals w higher mutation rates have higher fitness ONLY when exposed to novel, highly variable environments