Biology 12: Genetics and Evolution

Question 1

penetrance

Answer 1

the proportion of individuals in the population carrying the allele who actually express the phenotype

the probability that you express the phenotype if you have the genotype

a population measure

full > high > reduced > low > nonpenetrance

Question 2

expressivity

Answer 2

the different manifestations of the same genotypes across the population

having varying phenotypes despite have the same genotype

individual measure

constant > variable

Question 3

genetic leakage

Answer 3

a flow of genes between species

individuals from closely related species can mate to produce hybrid offspring

Question 4

genetic drift

Answer 4

changes in the composition of the gene pool due to chance

tends to be more pronounced in small populations

Question 5

founder effect

Answer 5

extreme case of genetic drift

a small population of a species is in reproductive isolation from other populations

since breeding group is small, inbreeding may occur

increase in homozygous genotypes - ultimately cause a reduction in genetic diversity

Question 6

inbreeding depression

Answer 6

loss of genetic variation causing reduced fitness of a population

Question 7

outbreeding / outcrossing

Answer 7

the introduction of unrelated individuals into a breeding group

could result in increased variation in a gene pool and increased fitness

Question 8

test cross

Answer 8

used to determine an unknown genotype

organism with an unknown genotype is crossed with an organims known to be homozygous recessive

sometimes called back cross

Question 9

allele frequency

Answer 9

how often an allele appears in a population

Question 10

what are the five conditions for Hardy-Weinberg equilibrium (population not undergoing evolution)?

Answer 10

• population is very large (no genetic drift)
• there are no mutations that affect the gene pool
• mating between individuals is random (no sexual selection)
• no migration of individuals into or out of population
• genes in population are all equally successful at reproducing

Question 11

what are the equations for Hardy-Weinberg equilibrium?

Answer 11

p + q = 1

p² + 2pq + q² = 1

p - T

q - t

p² - TT

2pq - Tt

q² - tt

Question 12

natural selection

Answer 12

survival of the fitness

theory that chance variations exist between individuals; advantageous variations (that increase an individual’s fitness for the environment) afford the most opportunity for reproductive success

Question 13

modern synthesis model / neo-darwinism

Answer 13

accounts for mutation and recombination as mechanisms of variation and considers differential reproduction to be the mechanism of reproductive success

when mutation/recombination results in a favorable change in reproductive success, that change is more likely to be passed on to the next generation

Question 14

inclusive fitness

Answer 14

a measure of an organism’s success in the population

based on # of offspring, sucess in supporting offspring, ability of offspring to support others

Question 15

theory of punctuated equilibrium

Answer 15

theory suggests that changes in some species oveer in rapid bursts rather than evenly over time

Question 16

stabilizing selection

Answer 16

a form of natural selection

keeps phenotypes within a specific range by selecting against extremes

ex. fetuses that weigh too little may be too healthy to survive, and fetuses weighing too much may experience trauma during birth

Question 17

directional selection

Answer 17

a form of natural selection

moves the average phenotype toward one extreme through adaptive pressure

ex. antibiotic resistance

Question 18

disruptive selection

Answer 18

a type of natural selection

two extreme phenotypes are selected over the norm

faciliated by polymorphisms - naturally occuring differences in form between members of the same population

ex. medium sized bird gives rise to birds with large or small beaks that are easier to break large or small nuts

Question 19

adaptive radiation

Answer 19

the rapid rise of a number of different species from a common ancestor

allows various species to occupy different niches

favored by environmental changes or isolation of small groups of the ancestral species

Question 20

niche

Answer 20

a specific environment (habitat, available resources, predators) for which a species can be specifically adapted

Question 21

species

Answer 21

the largest group of organisms capable of breeding to form fertile offspring

Question 22

what is the difference between prezygotic and postzygotic methods of reproductive isolation?

Answer 22

prezygotic mechanisms prevent formation of the zygote completely

ex. breeding at different times (temporal isolation), different niches (ecological isolation), lack of attraction between species (behavioral isolation), incompatible anatomy (reproductive isolation)

postzygotic mechanisms allow for gamete fusion but yield either nonviable or sterile offspring

ex. hybrid inviability (zygote can’t develop to term), hybrid sterility (hybrid can’t reproduce) , hybrid breakdown (first generation an reproduce but second cannot)

Question 23

divergent evolution

Answer 23

the independent development of dissimilar characteristics in two or more lineages sharing a common ancestor

caused by species living in different environments and adapting to different selection pressures while evolving

Question 24

parallel evolution

Answer 24

related species with a common ancestor evolve in similar ways for a long period of time in response to analogous environmental selection pressures

Question 25

convergent evolution

Answer 25

the independent development of **similar characteristics** in two or more lineages **not sharing a recent common ancestor** species evolved certain similar features in similar enviornments

Question 26

molecular clock model

Answer 26

model with proposes that the **degree of difference in the genome** between two species is related to the **amount of time since the two species broke off from a common ancestor**

Question 27

recombination frequency

Answer 27

the likelihood that two alleles are **separated from each other** during crossing over **roughly proportional to the distance between the genes** on the chromosome **tightly linked genes have recombination frequencies close to 0%** **weakly linked genes have recombination frequencies appraching 50%** (expected because of independent assortment)