Lecture 5: Genetic Variation (models and measurement)

Question 1

Who provided the foundations for “Neo-Darwinism” and the “New Synthesis”?

Answer 1

Fisher, Haldane, and Wright.

Question 2

What is Neo-Darwinism?

Answer 2

An attempt to reconcile mendel’s laws of genetics (which claim organisms do not change) with Darwin’s theory of evolution—which claims they do.

Question 3

What factors influence patterns of genetic diversity and evolution? Which increase diversity and which decrease?

Answer 3

1. mutation (increase)
2. recombination (increase)
3. migration (increase)
4. genetic drift (decrease)
5. Natural selection (decrease/increase)

Question 4

What is the ultimate source of genetic variation?

Answer 4

Mutation which is caused by errors during replication.

Question 5

Purifying/negative selection

Answer 5

mutations that reduce fitness and are removed by natural selection

Question 6

Positive selection (adaptation)

Answer 6

mutations that increase fitness will become fixed in a population

Question 7

Selection favouring diversity

Answer 7

natural selection acting to maintain diversity over long term (heterozygote advantage)

Question 8

How does migration affect diversity?

Answer 8

Gene flow influences the structuring of diversity over a large spatial scale.

Question 9

Polymorphism

Answer 9

Proportion (p) of gene loci that are polymorphic. a gene is polymorphic if more than one allele occupies that gene locus within a population. Each diff. gene must occur at rate of at least 1%.

Question 10

Heterozygosity

Answer 10

Average frequency of heterozygous individuals per gene locus. Heterozygous + the possession of 2 different alleles of a particular gene.

Question 11

Theories of what maintains genetic variation?

Answer 11

1. Mutation-selection balance
2. Selection maintaining variation
3. Variation selectively neutral

Question 12

Mutation-selection balance

Answer 12

Less fit types maintained by repeat mutation

Question 13

Selection maintaining variation

Answer 13

Heterozygote advantage, frequency-dependent selection, fitness varies in space and time.

Question 14

Variation selectively neutral

Answer 14

Theory developed by Motoo Kimura. Different types do not differ in their fitness hence none eliminated by selection.

Question 15

Population Genetic Variation: Classical School

Answer 15

• Morgan and Muller
• negative selection
• low heterozygosity
• low polymorphism
• wild type is normal genotype

Question 16

Population Genetic Variation: Balance School

Answer 16

• Dobzhansky and Ford
• heterozygote advantage
• high heterozygosity
• high polymorphism
• selection favours diversity

Question 17

What was early quantitative evidence for existence of genetic variation?

Answer 17

Artificial selection experiments done on groups of organisms (done on drosophila and maize). Selection responses demonstrate that abundant genetic variation exists for polygenic traits but didn’t give any info on polymorphism or heterozygosity.

Question 18

Who was Richard Lewontin and what did he do?

Answer 18

Used electrophoresis and allozymes to figure out which genes are variable (polymorphic). He initiated large scale surveys of electrophoretic variation in enzymes and proteins in diverse organisms.

Question 19

Define electrophoresis and allozyme.

Answer 19

Electrophor. - technique used to separate charged molecules.
Allozyme - allelic variants of the same protein. Differs by single allele (one mutation) at a single locus. Very useful in identifying differences between species within the same genus.

Question 20

Advantages of enzyme polymorphism?

Answer 20

• many loci can be examined
• can be used in nearly any organism
• loci co-dominant, heterozygotes can be identified
• variation examined close to DNA level
• Provides genetic marker loci for other studies

Question 21

Genetic variation in human population (# genes studied, P, and H)?

Answer 21

71 genes studied, P = 0.28, H = 0.07

Question 22

What is the rate of DNA polymorphism in humans? What about E. coli?

Answer 22

humans - 1 per 1000 base pairs

E. coli - 1 per 20 base pairs

Question 23

Humans show a loss of what with increasing distance from East Africa?

Answer 23

Genetic variation (reflects founder event as humans migrated)

Question 24

Which species has more genetic diversity: Maize or Teosinte?

Answer 24

Teosinte, wild ancestral species of Maize displays more diversity.