Chapter 15 | Molecular Evolution

Question 1

define the neutral theory of molecular evolution

Answer 1

the majority of mutations are neutral, and may fix in populations through genetic drift

Question 2

rate of fixation of neutral mutations by genetic drift is

Answer 2

independent of population size

Question 3

rate of fixation is equal to

Answer 3

the neutral mutation rate

Question 4

what is meant by most of mutations are neutral?

Answer 4

they serve no benefit or non-benefit to the survival of the organism

Question 5

to the random fluctuation of allele frequencies in a population from one generation to the next due to chance events

Answer 5

genetic drift

Question 6

if most mutations are neutral, and the mutation rate is constant

Answer 6

macromolecules evolving in different populations should diverge from one another at a constant rate

Question 7

why do most nucleotide changes in coding regions have no effect at the protein level?

Answer 7

most amino acids are specified by more than one codon, often ending up being a silent change

Question 8

a substitution that does not change the amino acid

Answer 8

synonymous or silent substitution

Question 9

a substitution that does cause a change in the amino acid

Answer 9

nonsynonymous substitution (from a missense mutation)

Question 10

nonsynonymous substitutions are often

Answer 10

deleterious

Question 11

protein shape and function is not always altered in nonsynonymous substitutions, so it may be

Answer 11

selectively neutral or possible beneficial

Question 12

which substitution occurs more frequently than the other?

Answer 12

synonymous substitutions

Question 13

are the rates of nonsynonymous substitutions equal in all genes?

Answer 13

no; they vary, and are higher in some genes than others

Question 14

what does a ratio of 1 between synonymous and nonsynonymous substitutions suggest?

Answer 14

the amino acid replacement is neutral

Question 15

copies of genes that are no longer functional

Answer 15

pseudogenes

Question 16

evolutionary rates are

Answer 16

higher in pseudogenes

Question 17

synonymous / nonsynonymous < 1

Answer 17

the amino acid is under position selection for change

Question 18

synonymous / nonsynonymous > 1

Answer 18

the amino acid is under purifying selection

Question 19

what allows scientists to determine history and timing of synonymous and nonsynonymous substitutions?

Answer 19

comparing gene sequences among species

Question 20

defense mechanism against bacteria

Answer 20

lysozyme

Question 21

what is evolutionary convergence?

Answer 21

unrelated organisms develop similar traits or characteristics independently as they adapt to similar environmental challenges

Question 22

the probability of fixation for all three codon positions

Answer 22

are influenced by selection

Question 23

regions of chromosomes can be duplicated through

Answer 23

chromosomal mutations

Question 24

what are some fates of duplicate genes?

Answer 24

(1) both copies retain original function (more product can be made)
(2) one copy becomes nonfunctional and turns into a pseudogene
(3) both copies retain original function but expression diverges in different tissues or at different times
(4) one copy accumulates substitutions that allow it to perform new function

Question 25

genomes contain all the genes needed to form a complete organism, but it must

Answer 25

be expressed at specific times and in specific tissues

Question 26

what can changes in gene expression account for?

Answer 26

a majority of the evolution of diverse body forms

Question 27

genes that control body axis orientation and segmentation during development are

Answer 27

conserved across a diversity of organisms

Question 28

maternal effect genes

Answer 28

set up the major axes of the embryo

Question 29

gap genes

Answer 29

organize broad areas

Question 30

pair rule genes

Answer 30

divide embryo into units of two segments each

Question 31

segment polarity genes

Answer 31

determines boundaries and anterior-posterior organization in individual segments

Question 32

hox genes are expressed

Answer 32

in different combinations along the length of the embryo

Question 33

the expression of hox genes

Answer 33

determines the morphology of each segment

Question 34

hox genes are in two clusters,

Answer 34

ordered the same as their spatial expression in the embryo

Question 35

antennapedia mutation

Answer 35

legs grow in place of antennae

Question 36

bithorax mutation

Answer 36

an extra pair of wings grow

Question 37

a large number of homologous genes

Answer 37

control development in distantly related species

Question 38

genetic toolkit

Answer 38

regulatory genes that govern development processes that have been highly conserved throughout evolution

Question 39

genetic switches that determine where and when genes are expressed

Answer 39

underlie both development and the evolution of differences amongst species

Question 40

what is the Hox gene Ubx involved in?

Answer 40

producing morphological differences in thoracic and abdominal appendages

Question 41

heterometry

Answer 41

altered quantity of gene expression of a developmental gene

Question 42

heterochrony

Answer 42

altered timing of gene expression of a developmental gene

Question 43

heterotopy

Answer 43

altered spatial pattern of gene expression of a developmental gene

Question 44

positive selection

Answer 44

beneficial amino acid changes are being favored and fixed in the population

Question 45

purifying selection

Answer 45

harmful genetic variations are being removed from the population

Question 46

segmentation genes

Answer 46

define segment number and orientation of each segment