Week 5

Question 1

Sympatric Speciation

Answer 1

Natural selection overcomes gene flow and causes speciation of populations despite no physical isolation

Question 2

Assortative Mating

Answer 2

Favor individuals with similar characteristics to others

Question 3

What are the two mechanisms of sympatric speciations

Answer 3

disruptive selection and polyploidization

Question 4

Disruptive selection as a mechanism of sympatric speciation

Answer 4

natural selection for different habitats or resources cause divergence - must be coupled with assortative mating

Question 5

Polyploidization

Answer 5

genetic isolation is created by formation of polyploid individuals that can breed only with each other

Question 6

Types of polyploidization

Answer 6

Autopolyploidy and allopolyploidy

Question 7

Autopolyploidy

Answer 7

polyploids have duplicate chromosome sets from same species (e.g. a chromosome doubling to produce a tetraploid)

Question 8

Allopolyploidy

Answer 8

polyploids have chromosome sets from different species (they originate with a hybridization event, followed by chromosome doubling)

Question 9

Explain the example of the Soapberry bug for disruptive selection

Answer 9

-bugs use beaks to reach seeds inside fruits
-variation in fruit size between nonnative (small) and native (large) causes the population to diverge into a short beaked population and a long beaked population

Question 10

Explain the example of the maidenhair fern as it relates to polyploids

Answer 10

-Example of autopolyploidy
-this species contains diploid and tetraploid individuals
-tetraploids are the offspring of a diploid gamete that is self fertilized
-tetraploid individuals can breed with other tetraploids but not diploids

Question 11

How do allopolyploid species form

Answer 11

-species 1 and 2 undergo meiosis and produce a hybrid individual
-hybrid individual have less efficient homologous pair recognition causing an increase in chance for error during meiosis
-an error in meiosis causes the formation of an allopolyploid cell which has two copies of each chromosome
-a gamete with the same number of cells as the hybrid individual fuses with another identical cell to form a offspring with twice the ancestral genome (diploid to tetraploid)
-leads to reproductive isolation

Question 12

How does a polyploid cell lead to isolated reproduction

Answer 12

if the polyploid and the original species attempt to mate they will produce a species with an odd number of chromosomes whose gametes rarely contain the same number of each type of chromosome causing dysfunctional number of chromosomes and the inability to reproduce

Question 13

Why is speciation by polyploidization more common in plants than animals

Answer 13

somatic cells of plants that have undergone many rounds of mitosis may then undergo meiosis and produce a polyploid gamete, also self fertilization is more common in plants

Question 14

Adaptive introgression

Answer 14

process in which advantageous genetic variation is transferred from one species (or populatiom) to another

Question 15

Homogenization

Answer 15

When gene flow occurs and may erase distinctions between two populations

Question 16

Possible outcomes of hybridization

Answer 16

homogenization, adaptive introgression, reinforcement, development of hybrid zones and speciation by hybridization

Question 17

What happens when isolated populations come into contact

Answer 17

when prezygotic isolation dose not exist, populations may interbreed to produce hybrids

Question 18

Reinforcement

Answer 18

Selection for traits that isolate populations reproductively - assortative mating
-occurs because of natural selection
-If two populations of differenct speices are extensively diverged, their hybrid offspring may have lower fitness - incomplete postzygotic isolation

Question 19

Explain the Wolf example from lecture on hybrid speciation

Answer 19

Red wolves have mitochondrial DNA that is derived from either the gray wolf or coyotes, they could either be from hybrid origin or there could have been extensive gene flow for mtDNA
-Some wolves have a percentage of coyote DNA
-Red wolves are 24% wolf and 76% coyote
-coyotes are a combination of coyote, wolf and dog DNA

Question 20

Internal Nodes on Phylogenetic tree

Answer 20

represent ancestors of the descendant taxa

Question 21

Ancestral Node/ root on phylogenetic tree

Answer 21

represents oldest ancestor on tree

Question 22

Polytomy

Answer 22

3 way split on a phylogenetic tree where there is not enough data to further classify

Question 23

Homology

Answer 23

occurs when traits are similar due to shared ancestry

Question 24

Homoplasy

Answer 24

when traits are similar for reasons other than common ancestry

Question 25

Convergent evolution

Answer 25

when natural selection favors similar solutions to the problems posed by a similar way of life - common cause of homoplasy

Question 26

How do researchers estimate phylogenies

Answer 26

they analyze characteristics of species to infer phylogenetic relationships among species

Question 27

Strategies for estimation trees

Answer 27

phenetic (distance), cladistic (maximum parsimony), maximum likelihood and bayesian

Question 28

Synapomorphy

Answer 28

a novel trait that a clade of organisms have and that others outside this clade lack

Question 29

What is the purpose of Hox genes

Answer 29

to regulate differentiation within the adult and embryo

Question 30

How do we know that Hox genes of humans and fruit flies are homologous

Answer 30

similar DNA sequence, similar genomic organization, similar expression patterns during development similar function, other species closely related to fruit flies and humans also have Hox genes Max

Question 31

Maximum parsimony

Answer 31

logic that assumes that the best explanation or pattern is the one that implies the least amount of change

Question 32

Cryptic species

Answer 32

Many species are not easily distinguished by morphology animal and plant parts also sometimes not easily identified, most diverse parts of the world are least known

Question 33

DNA barcoding

Answer 33

-inventory of biodiversity -automate and expeditated species identification -classifies based on DNA sequence of one gene

Question 34

Atavism

Answer 34

an ancestral characteristic that is lost but then re-emerges during evolution

Question 35

In situ diversification

Answer 35

single ancestor disprses across islands and then diversifies -each species exploits different aspects of the environment -Not overly diverse

Question 36

Ecotypes

Answer 36

genetic variation within a species that allows it to exploit a particular environment

Question 37

Frog dispersal onto island

Answer 37

mainland frogs dispersed and then under went adaptive radiation into different ecotypes

Question 38

Parental care in fanged frogs

Answer 38

some carry tadpoles on back others guard eggs, some use internal incubation

Question 39

Did fanged frogs undergo an adaptive radiation

Answer 39

-diverse and closely related species that vary in useful trait -trait variation is correlated with environmental variation -some adaptive radiations exhibit species for species matching