Chapter 20 - Genes within Populations

Question 1

Basis of evolutionary change

Answer 1

Genetic variation

Question 2

Evolution

Answer 2

change in the genetic makeup of a population over time

Question 3

Jean Baptist Lamark (1802)

Answer 3

Inheritance of acquired characteristics - use and disuse
Theory: variation is acquired
Ex. Proposed ancestor of giraffes has characteristics of modern-day okapi. The giraffe ancestor lengthened its neck by stretching to reach tree leaves, then passed the change to offspring.

Question 4

Charles Darwin

Answer 4

Descent with modification “Natural Selection”
* Organisms produce more offspring than will survive - resources are limited, the more fit individuals will survive
* Populations are highly variable
* Variability is inherited - not acquired, genetic make-up of the population will change
* Resources are limited so there is a struggle to survive - if there are unlimited resources, there is no driving force for change, if carrying capacity is reached, the fight to survive is reached
* Animals best adapted survive and reproduce
* Inherited traits become more prevalent in the population - change in the genetic make-up overtime
Theory: variation is inherited
Ex. Some individuals born happen to have longer necks. Over many generations, longer-necked individuals are more successful, perhaps because they can feed on taller trees, and pass the long-neck trait to their offspring.

Question 5

How does genetic variation arise?

Answer 5

• Mutation - ultimate source of variation - can happen spontaneously, chemicals, or just random
• Crossing over and random assortment in meiosis
• Sexual reproduction results in new genetic combinations - bringing haploid together and forming new genetic combinations, faster evolution than asexual reproduction

Question 6

Population genetics

Answer 6

study of properties of genes in a population

Question 7

Gene pool

Answer 7

sum of all the alleles of all genes in a population

Question 8

Alleles

Answer 8

alternate form of a gene

Question 9

If a gene has two alleles then what is the sum of the frequency of the alleles?

Answer 9

1

Question 10

Hardy – Weinberg Principle

Answer 10

helps determine allele frequencies by using the following equation:

• p2 + 2pq + q2 = 1 ; p + q = 1
• p2 = homozygous dominant
• 2pq = heterozygous
• q2 = homozygous recessive

Question 11

Hardy – Weinberg Principle

Answer 11

helps determine allele frequencies by using the following equation:

• p2 + 2pq + q2 = 1 ; p + q = 1
• p2 = homozygous dominant
• 2pq = heterozygous
• q2 = homozygous recessive

gives us a base line to measure change in a population

Question 12

Hardy – Weinberg Principle conditions

Answer 12

• Large population size
• Random mating occurs
• No mutation
• No gene flow
• No selection

Question 13

5 agents of evolutionary change

Answer 13

Mutation
Gene flow
Nonrandom mating
Genetic Drift
Natural Selection

Question 14

Mutation

Answer 14

new forms of DNA occur - increase in variation - alleles will change

Question 15

Gene flow

Answer 15

exchange of genes between populations - (same species) population A and population B exchanging, movement of species

Question 16

Nonrandom mating

Answer 16

mate selection - selecting mates depending on traits wanted or needed, inbreeding

Question 17

Genetic Drift

Answer 17

change in allele frequency of small populations - small populations are greatly affected by movement, likelihood of extinction, inbreed, complications

Question 18

Founder effect

Answer 18

Sometimes one or a few individuals disperse and become the founder of a new, isolate population at some distance from their place of origin. Common in islands, migration from one location to another because of some event, starting a new “colony”

Question 19

Bottleneck effect

Answer 19

Even if organisms do not move from place to place, occasionally their populations may be drastically reduced in size. Result from flooding, drought, disease, etc. small population, chance event, genetic make-up becomes limited

Question 20

Natural Selection

Answer 20

• Variation in populations - natural selection works by favoring individuals with some traits over individuals with alternative traits
• Differential reproductive success of individuals - some individuals are more successful than others in producing offspring
• Variation is inherited

Question 21

Fitness

Answer 21

• Reproductive success, leaving behind the most offspring

* Is a combination of survival, mating success, and # of offspring/mating

Question 22

Mutation vs. natural selection

Answer 22

mutation rates are rarely high enough to overcome the effect of natural selection - doesn’t have high rate of mutation to beat natural selection but it can happen

Question 23

Genetic drift vs. natural selection

Answer 23

drift may by its nature reduce or remove adaptive genes from a population - rare genes or abundant genes can be removed

Question 24

Gene flow vs. natural selection

Answer 24

gene flow may be a constructive or constraining force on natural selection

Question 25

Frequency

Answer 25

Natural selection’s role in maintaining variation
dependent selection
Fitness of a phenotype depends upon its frequency

Question 26

Negative frequency

Answer 26

dependent - rare phenotypes are preyed upon less, variation is maintained - animals, predators have search images, they look for what they usually eat and ignore the odd, the odd survives
Ex. search image

Question 27

Positive frequency

Answer 27

dependent selection has the opposite effect. Rare phenotypes eaten, reducing variation - rare doesn’t usually survive, can be easily preyed upon
Ex. oddballs, attracts attention

Question 28

Oscillating Selection

Answer 28

selection that favors one phenotype at one time, and another phenotype at other times
Ex. Galapagos finches, drought (more large seeds)

Question 29

Heterozygote Advantage

Answer 29

• individuals with copies of both alleles are favored
  Ex. Sickle cell anemia - malaria infects red blood cells, sickle cells protection from malaria, heterozygote have an advantage

Question 30

Forms of Selection

Answer 30

How selection changes a population depends on which genotypes are favored

Question 31

Disruptive Selection

Answer 31

diversifying selection, large and small are favored but not medium
Ex. bird beaks, small and large seeds only

Question 32

Directional Selection

Answer 32

moving towards one direction

Question 33

Stabilizing Selection

Answer 33

extreme are not favored, selecting middle

Ex. Babies birth weight, mortality