Chapter 23 Evolution of Populations (microevolution)

Question 1

What makes evolution possible?

Answer 1

Genetic variations.

Question 2

What is the source of new variations? (3)

Answer 2

1. Mutation in germ lines => new alleles
2. Chromosomal changes (meiosis)
3. Sexual reproduction

Question 3

What causes the banding patterns in a karyotype?

Answer 3

Banding patterns result from staining techniques that reveal differences in chromatin structure and base composition.

Question 4

How do base compositions affect staining?

Answer 4

1. AT-rich regions stain darker
2. GC-rich regions stain lighter

Question 5

What happens when homologous chromosomes align during meiosis?

Answer 5

They pair up to form a bivalent (or tetrad), bringing non-sister chromatids close together.

Question 6

What is crossing over?

Answer 6

At chiasmata, non-sister chromatids exchange segments, mixing alleles from both parents. *HELPS with genetic diversity

Question 7

(Prophase I)?

Answer 7

recombination/crossing over

Question 8

(Metaphase I & Anaphase I)

Answer 8

independent assortment

Question 9

What happens to homologous chromosomes during metaphase I of meiosis?

Answer 9

Tetrads (maternal & paternal homologs) line up randomly on the metaphase plate.

Question 10

How many combinations are possible in humans?

Answer 10

With n = 23, there are 2²³ ≈ 8.4 million combinations per gamete — or ~70 trillion combinations when combining two gametes! ***2^46

Question 11

How to measure heterozygosity?

Answer 11

IF 2: (H) = 2pq -> measure of population variation/ diversity at a single locus
IF 3: 1-(p^2)+(q^2)+(r^2)

Question 12

What is equation for genotypic frequency?

Answer 12

2: (p+q)2 = p2 + 2pq +q2
3: (p + q + r)2 = p2 + q2 + r2 + 2pq + 2pr + 2qr

Question 13

How is heterogeneity measured?

Answer 13

need heterozygosity averaged over many loci -> ‘average heterozygosity’ (Have)

Question 14

What is A?

Answer 14

allelic allelic diversity, pop. measure of average number of alleles per locus

Question 15

What is the Hardy-Weinberg Equilibrium?

Answer 15

The values of the allele frequencies (p & q) stay the same from one generation to the next, to the next, to the next…

Question 16

What is happening when the Hardy-Weinberg Equilibrium is compromised?

Answer 16

Changing allele frequencies between generations is evolution at work, specifically, microevolution.

Question 17

Mechanisms (5)

Answer 17

(1) mutations
(2) gene flow
(3) genetic drift
(4) natural selection
(5) nonrandom mating/inbreeding

Question 18

Mutation mechanism?

Answer 18

• changes in heritable DNA
• odds 1:50 to 1:5 any individual
• sperm carries mutation, mutation can be neutral, deleterious, lethal, advantageous

Question 19

Gene flow mechanism definition?

Answer 19

Movement of alleles between populations.

Question 20

Gene flow mechanism?

Answer 20

Through migration of individuals or gametes (e.g., pollen).
Increases genetic diversity; can make populations more genetically similar.

Question 21

Genetic drift definition?

Answer 21

Random changes in allele frequencies due to chance events.

Question 22

Genetic drift mechanism?

Answer 22

Especially strong in small populations (e.g., bottleneck or founder effect). Can lead to loss of genetic variation and fixation/loss of alleles.

Question 23

How did the Pleistocene Ice Age affect cheetah populations?

Answer 23

Glaciations caused habitat loss and a severe population bottleneck, drastically reducing cheetah genetic diversity.

Question 24

How does habitat fragmentation affect genetic diversity?

Answer 24

Isolated populations experience reduced gene flow and more inbreeding, which can lower genetic variation and fitness.

Question 25

What is the founder effect?

Answer 25

When a new population is started by a small number of individuals, leading to a limited gene pool.

Question 26

Natural selection definition?

Answer 26

Differential survival and reproduction based on inherited traits.

Question 27

Natural selection mechanism?

Answer 27

Individuals with traits better suited to the environment leave more offspring. Increases frequency of advantageous alleles, driving adaptation.

Question 28

What is adaptive evolution?

Answer 28

A process whereby traits that enhance reproduction or survival tend to increase in frequency over time.

Question 29

What is F?

Answer 29

Inbreeding coefficient.

Question 30

What is Ho and He?

Answer 30

Ho: 2pq(1-F) He: 2pq

Question 31

What is equation for F?

Answer 31

F = 1 - Ho/He

Question 32

What are the three ways natural survival increases these frequencies?

Answer 32

1. Directional selection 2. Stabilizing selection 3. Disruptive selection

Question 33

What is directional selection?

Answer 33

Favors one extreme phenotype over others. Shifts the overall trait distribution in one direction.

Question 34

What is stabilizing selection?

Answer 34

Favors the intermediate phenotype, against both extremes. Reduces variation and maintains the status quo.

Question 35

What is disruptive selection?

Answer 35

Favors both extremes, but not the intermediate trait. Can lead to two distinct forms in the population.

Question 36

Two ways to reduce unfavourable traits, but rarity occurs?

Answer 36

1. Diploidy 2. Balancing selection

Question 37

What is diploidy?

Answer 37

Organisms have two sets of chromosomes—one from each parent. It allows recessive alleles to be hidden in heterozygotes, preserving genetic variation in a population even if the allele isn’t currently beneficial.

Question 38

What are three subgroups of balancing selection?

Answer 38

1. heterozygous advantage 2. habitat selection 3. frequency-dependent selection

Question 39

What is balancing selection?

Answer 39

two or more phenotypes maintained in stable proportions

Question 40

What is heterozygous advantage?

Answer 40

Heterozygotes have a higher fitness than either homozygote.

Question 41

What is habitat selection?

Answer 41

Individuals choose environments where they survive or reproduce best. Can lead to genetic divergence if subgroups prefer different habitats (a step toward speciation).

Question 42

What is frequency-dependent selection?

Answer 42

The fitness of a trait depends on how common it is in the population.

Question 43

Negative and Positive of F-D selection?

Answer 43

Negative: Rare traits are favored (e.g., predator avoids unfamiliar prey colors). Positive: Common traits are favored (e.g., mimicry where survival improves if many share the same warning color).