genetics & evolution

Question 1

penetrance

Answer 1

proportion of individuals with an allele that express the phenotype associated with the allele

Question 2

expressivity

Answer 2

varying phenotypes despite identical genotypes; may be a range of possible phenotypes

Question 3

Mendel’s first law- of segregation

Answer 3

an organism has two alleles for each gene, one inherited from each parent; if two alleles are different, only dominant will be expressed

Question 4

law of independent assortment

Answer 4

inheritance of one gene does not affect inheritance of another gene; doesn’t account for linked genes

Question 5

Griffith study with rough (not virulent) and smooth (virulent/disease causing) pneumonia strains

Answer 5

If inject rough/non-virulent strain– mouse lives
If inject smooth strain– mouse dies
If inject heat killed smooth strain– mouse lives
If inject rough strain and heat-killed smooth strain–mouse dies– transformation: the live, nonvirulent bacteria acquired ability to form smooth capsules from dead, virulent bacteria

Question 6

Transposons

Answer 6

elements that can insert and remove themselves from the genome; if it inserts into the middle of a coding sequence, will disrupt the gene

Question 7

Inborn errors of metabolism

Answer 7

mutations that cause defects in genes required for metabolism

Question 8

genetic leakage

Answer 8

flow of genes between species

Question 9

genetic drift

Answer 9

changes in the composition of the gene pool due to chance

Question 10

founder effect

Answer 10

small population of a species ends up in reproductive isolation due to natural barriers or catastrophic events; as a result- inbreeding may occur, causes reduction in genetic diversity

Question 11

Monohybrid cross

Answer 11

only one trait is being studied

Question 12

Test cross

Answer 12

used to determine an unknown genotype; unknown genotype is crossed with homozygous recessive organism; if all dominant offspring- it was homozygous dominant, if 1:1 ratio, then it was heterozygous

Question 13

Dihybrid cross

Answer 13

consider two traits; observe a 9:3:3:1 ratio if cross two heterozygotes; easiest to solve by making two separate punnett squares

Question 14

sex-linked crosses

Answer 14

Use X and Y to symbolize the chromosomes, subscripts to represent alleles; males only need one recessive allele to express a sex-linked disease

Question 15

chiasma

Answer 15

point of crossing over during recombination

Question 16

recombination frequency

Answer 16

likelihood that two alleles will separate from each other during recombination, increases with distance of separation

Question 17

genetic mapping

Answer 17

one map unit/centimorgan corresponds to 1% chance of recombination occurring between two genes

Question 18

allele frequency

Answer 18

how often an allele appears in a population; ex. if you had 50 plants, you would have 100 alleles; if 75 of them were dominant, allele frequency= 75/100

Question 19

Hardy Weinberg Equilibrium conditions

Answer 19

large population size; no mutations in gene pool; random mating within population; no migration into or out of population; genes in pool are equally successful at reproducing

Question 20

Hardy Weinberg equations for a trait with two alleles, where p is dominant and q is recessive

Answer 20

p+q=1 (where p and q indicate allele frequencies)
p^2 + 2pq +q^2 = 1 (can get equation by squaring top one)
sum of p^2 and 2pq would represent dominant phenotype frequency

Question 21

modern synthesis model of evolution (neo- Darwinism)

Answer 21

updated form of Darwinism; when mutations occur that are favorable to the organism, the change is likely to be passed on to the next generation; it is the GENE POOL that evolves over time- populations evolve, not individuals

Question 22

Inclusive fitness

Answer 22

organism’s success in a population, based on number of offspring and ability to support offspring

Question 23

Altruistic behavior

Answer 23

may threaten an individual’s life, but can improve the success of the population as a whole by helping others

Question 24

Punctuated equilibrium

Answer 24

pattern of evolutionary change where long periods pass with little change followed by a brief period of rapid change; changes occur in short bursts

Question 25

Stabilizing selection

Answer 25

keeps phenotypes within a specific range by selecting against the extremes; ex. birth weight- fetus wont survive if too small or too large

Question 26

directional selection

Answer 26

dominance of an initially extreme phenotype; ex. emergence of bacteria that are resistant to antibiotics promotes survival

Question 27

disruptive selection

Answer 27

two extreme phenotypes are selected over the norm; ex. birds with either really long or really short beaks that can eat large or small seeds

Question 28

polymorphisms

Answer 28

naturally occurring differences between members of same population

Question 29

adaptive radiation

Answer 29

rapid rise of many different species from a common ancestor

Question 30

bottleneck effect

Answer 30

occurs when there is a disaster of some sort that reduces a population to a small handful, which rarely represents the actual genetic makeup of the initial population. This leaves smaller variation among the surviving individuals

Question 31

Prezygotic mechanisms of reproductive isolation

Answer 31

prevent formation of zygotes between two populations that had initially been same species; ex: breed at different times, lack of attraction between members of two species

Question 32

postzygotic mechanisms

Answer 32

allow for gamete fusion but yield nonviable offspring

Question 33

Divergent evolution

Answer 33

more than one lineage that share a common ancestor diverge into different characteristics due to exposure to different environments

Question 34

parallel evolution

Answer 34

related species evolve in similar ways in response to similar environmental pressures

Question 35

convergent evolution

Answer 35

multiple unrelated species develop similar characteristics in response to similar environmental pressures

Question 36

molecular clock model

Answer 36

the more similar the genomes between two species, the more recently the two separated from a common ancestor