Lecture 4 - Population Genetics

Question 1

Population

Answer 1

a group of individuals interbreeding and producing fertile offspring

Question 2

Explain how a drought effected the finches of the Galapagos, specifically their beak size and explain why this occured

Answer 2

• > a catastrophic drough left only 180 of 1200 birds alive
• > the majority of the remaining birds had large beaks and they had a greater chance of survival during the drought because larger, harder seeds are more prominant during a drought
• > this event influences the next generation as there were more individuals with larger beaks

Question 3

Genetic Variation

Answer 3

• > alternative versions of genes (alleles; one from mom, one from dad) account for variations in inherited characters

Question 4

Law of segregation

Answer 4

two alleles of a single trait will separate randomly, meaning that there is a 50% either allele will end up in either gamete

Question 5

Law of independnat assortment

Answer 5

the allele of one gene separates independently of an allele of another gene.

Question 6

What are the sources of genetic variation

Answer 6

• > sexual recombination
• > mutations

Question 7

Sexual recombination

Answer 7

When there is no change in allele frequencies but there are different combination of genes (law of independant assortment)

Question 8

Allele Frequencies

Answer 8

a measure of the relative frequency of an allele on a genetic locus in a population

• > 2/homozygous + 1/ heterozygous % total number of alleles

(p and q represent frequencies)

*p + q = 1*

Question 9

Hardy - Weinberg Principle

Answer 9

*p^2 + 2pq + q^2*

• > the Hardy - Weinberg equation calculates the expected frequency of genotypes from allele frequency

H-W Principle

• frequencies of alleles and genotypes in a population remain constant from generation to generation

• > if gametes contribute to the next generation randomly, allele frequencies will not change
• > the principle describes a population that is not evolving, this principle does not hold if it is evolving

Question 10

5 conditions for non-evolving populations rarely met in nature

Answer 10

1. No mutations
2. Random mating
3. Large population size
4. No gene flow
5. No natural selection

Question 11

In real populations, do allele and genotype frequencies change over time?

Answer 11

Yes

Question 12

3 factors that bring about most evolutionary change

Answer 12

1. Natural Selection
2. Genetic Drift
3. Genetic flow

Question 13

Natural selection acts upon what?

Answer 13

acts on phenotype

• > favors certain genotypes by acting on phenotypes

adaptive evolution

Question 14

Genetic Drift

Answer 14

allele frequency is changed by chance

• > reduces genetic variation through loss of alleles
• > important for small populations

Question 15

How are small populations created

Answer 15

1. the founder effect (finches)
   - > a few individuals isolated from larger population
   - > allele frequency in founder population different from parent population
2. the bottleneck effect
   - > sudden reduction in population size (i.e. fire or flood)
   - > resulting gene pool different from parent population

Question 16

Gene flow

Answer 16

the transfer of genetic variation from one population to another (i.e. pollen carried by wind)

• > genetic flow reduces variation among populations over time