ch22-24

Question 1

whats the equation for genotypic frequency?

Answer 1

p^2 + 2pq + q^2 =1

Question 2

whats the equation for allelic frequency?

Answer 2

p + q = 1

Question 3

Describe why it isn’t possible for an individual to evolve in its lifetime.

Answer 3

individuals do not evolve, populations evolve over time. natural selection can only increase or decrease the heritable traits that vary in the population and adaptations vary with different environments.

Question 4

describe why natural selection is not a random process

Answer 4

descent with modification produces diversity through natural selection. its an accumulation of adaptations due to the heritable traits being passed onto more offspring than can survive in the environment which then causes individuals which are more suited to the environment to leave more offspring. overtime these favourable traits accumulate in the population.

Question 5

describe whats required for natural selection to occur

Answer 5

• characters must vary
• variation must be heritable
• more offspring produced than survive
• characters confer differential survival/reproductive benefit

Question 6

describe the difference between homologous features and features that are similar due too homoplasy

Answer 6

homologous features: similarity resulting from common ancestry. vestigial structures.

homoplasy: similar due to convergent evolution (similar selection pressures). convergent evolution refers to the evolution of similar , or analogous features, it does not provide information about ancestry. analogous traits arise when groups independently adapt to similar environments in similar ways.

Question 7

Describe the mechanisms that cause allele frequency change

Answer 7

natural selection, genetic drift, and gene flow can change allele frequency.
natural selection: individuals that have certain inherited traits tend to survive and reproduce at higher rates than other individuals because of those traits.
genetic drift: chance fluctuations in allele frequencies over generations tend to reduce genetic variation.
gene flow:
may introduce alleles that are advantageous or disadvantageous.
both genetic drift and gene flow can increase the frequencies of alleles that enhance survival or reproduction.

Question 8

Explain why variation in heritable traits is a prerequisite for evolution.

Answer 8

genetic vairation among individuals is caused by differences in genes or other DNA segments. it refers to the genetic differences among individuals within a population.

Question 9

Describe what average heterozygosity is, and explain how it is an indicator of
variation within a population.

Answer 9

average heterozygosity: the average percent of loci that are heterozygous in population.
a higher avg heterozygosity suggests more genetic diversity within the population (, individuals within the population have a higher chance of carrying different alleles at various genetic loci)

Question 10

Describe what the sources of genetic variation are.

Answer 10

in sexually reproducing organisms: crossing over, independent assortment of chromosomes, fertilization.
the nucleotide differences that provide the basis for genetic mutation arise by mutation as well as other processes that produce new alleles and new genes

Question 11

Describe the conditions for Hardy-Weinberg

Answer 11

it describes a hypothetical population that’s not evolving.
irl, allele and genotype freqs do change over time.
- no mutations
if there are mutations or if entire genes are deleted/duplicated, gene pool is modified
- random mating
if inbreeding occurs, random mixing of gametes does not occur and so genotype frequencies change
- no natural selection
allele freqs change when individuals with different genotypes show consistent differences in their survival or reproductive success
- extremely large population size
in small pop. , allele freqs fluctuate by chance over time (genetic drift)
- no gene flow
if alleles move in or out of populations, gene flow can alter allele freqs

Question 12

Compare and contrast natural selection, genetic drift, and gene flow.

Answer 12

genetic drift: random, describes how allele frequencies fluctuate unpredictably from one generation to the next. it tends to reduce genetic variation thru losses of alleles.
gene flow:
transfer of genetic material (alleles) from one population to another, occurs when individuals migrate and interbreed with members of another population.
natural selection:
the process by which certain traits confer a reproductive advantage, leading to the increased prevalence of those traits in a population over time, operates based on the differential survival and reproduction of individuals with specific heritable traits.

Question 13

effect of gene flow, genetic drift, and natural selection on genetic variation

Answer 13

genetic drift:
can lead to the loss or fixation of alleles over generations, reducing genetic diversity
gene flow:
tends to homogenize the genetic composition of different populations, reduces genetic differentiation by introducing new alleles and increasing genetic diversity in populations that exchange genes.
natural selection:
can increase or decrease the frequency of alleles in a population depending on their impact on an organism’s fitness, acts to adapt populations to their environments by favoring traits that enhance survival and reproductive success. over time can accumulate advantageous alleles.

Question 14

Explain the statement “Only natural selection can lead to adaptive evolution.”

Answer 14

natural selection consistently leads to the accumulation of traits that improve the survival and reproductive success of individuals in their natural habitats.
evolution by natural selection involves both chance and ‘sorting’:
- new genetic variations arise by chance
- beneficial alleles are ‘sorted’ and favoured by natural selection
only natural selection consistently increases the frequencies of alleles that provide a reproductive advantage - therefore lead to adaptive evolution

Question 15

Give examples of natural selection, genetic drift, and gene flow.

Question 16

Describe directional selection, disruptive selection, and stabilizing selection.

Answer 16

directional selection:
favours individuals at one end of the phenotypic range
disruptive selection:
favours individuals are both extremes of the phenotypic range
stabilizing selection:
favours intermediate variants and acts against extreme phenotypes

Question 17

Give examples of directional selection, disruptive selection, and stabilizing
selection

Question 18

Compare and contrast intersexual selection and intrasexual selection.

Answer 18

intersexual selection: direct competition among individuals of one sex for mates of the opposite sex
intrasexual selection: mate choice, occurs when individuals of one sex (usually females) are choosy in mate selection

Question 19

Describe what is meant by “reproductive isolation”

Answer 19

the existence of biological factors (barriers) that impede two species from producing viable, fertile offspring

Question 20

Describe the five prezygotic barriers discussed in class, and give examples
for each type of barrier.

Answer 20

• habitat isolation
  two species that inhabit the same area but have different habitats may rarely encounter each other, even though they aren’t isolated by physical barriers
• temporal isolation
  species that breed during different times of the day, season, or years can’t mix their gametes
• behavioural isolation
  Courtship rituals attract mates and other behaviors unique to a particular species are effective reproductive barriers, even between closely related species. they enable mate recognition (a way to identify potential mates of the same species)
• mechanical isolation
  when mating is attempted but morphological differences prevent its successful completion
• gametic isolation
  sperm of one species may not be able to fertilize the eggs of another species. sperm may not be able to survive in the reproductive tract of a female, or biomechanisms may prevent the sperm from entering the membrane surrounding the egg.

Question 21

How do prezygotic barriers block fertilization?

Answer 21

prezygotic barriers: block fertilization from occurring by:
- impeding different species attempting to mate
- preventing successful completion of mating
- hindering fertilization if mating is successful

Question 22

Describe the three postzygotic barriers discussed in class, and give
examples for each type of barrier

Answer 22

• reduced hybrid viability
  genes of different parent
  species may interact in ways that impair the hybrid’s development or survival in its environment.
• reduced hybrid fertility
  Even if hybrids are vigorous, they may be sterile. If the chromosomes of the two parent species differ in number or structure, meiosis in the hybrids may fail to produce normal gametes. Since the infertile hybrids cannot
  produce offspring when they mate with either parent species, genes cannot flow freely between the species.
• hybrid breakdown
  Some first-generation hybrids are viable and fertile, but when they mate with one another or
  with either parent species,
  offspring of the next generation are feeble or sterile.

Question 23

How do postzygotic barriers prevent the hybrid zygote from developing in a
viable, fertile adult?

Answer 23

may contribute to reproductive isolation after the hybrid zygote is formed.
developmental errors may reduce survival among hybrid embryos.
problems after birth may also cause hybrids to be infertile or decrease their chance of surviving long enough to reproduce.

Question 24

Be able to look at different representations of phylogenetic trees and identify
ones that depict identical relationships.

Question 25

Draw a phylogenetic tree depicting an adaptive radiation.