BIS 2B Midterm 2 --practice questions

Last lecture we talked about r-selected and k-selected organisms. These terms come from the equations for population growth, in which r represents ___ __and K represents__ ___

r=growth rate, k=carrying capacity

For a population of 500 individuals, with r=0.25, what will the population be after 10 years?

Nt = Noe^(rt), 6091

Alcohol is produced as a byproduct of fermentation of sugar by yeast. The maximum ABV% that a solution can achieve is \~15% because yeast cannot survive in higher concentrations of waste products. Is this an example of density independent or density dependent control?

Density dependent. more individuals will produce more waste.

Is wildfire density dependent or density independent?

if you are a tree: density dependent, more trees closer together = fire easier to spread. if you are a human: density independent: doesn’t matter how many humans are in a fire, you will still burn.

What type of selection occurred in the fox farm experiment?

directional (shift towards tameness)

The e coli genome is 87.7% protein coding (compared to 1.5% in humans). . which of the following would you expect to be true?

mutations are more likely to be deleterious in e coli because the mutations are more likely to land in those protein coding regions

True or False: If the frequencies of genotypes in a given population add up to 1, then the population is in Hardy Weinberg equilibrium.

False

Which of the following is not a violation of Hardy-Weinberg assumptions?

there are ten different alleles at a particular locus

In many large mammal populations, highways can be barriers to movement- individuals rarely cross them. One solution to this problem has been to install overhead bridges for wildlife to safely cross. the goal is to increase gene flow between the populations on either side of the highway. Which of the following would you expect to see if the bridge is successful in its goal?

The two populations would become more genetically similar.

Genotype

The alleles you carry

Phenotype

An organism's physical appearance, or visible traits.

Homozygous

An organism that has two identical alleles for a trait

Heterozygous

An organism that has two different alleles for a trait

Medel's hypothesis

When to contrasting traits are bred, their characteristics are irreversibly blended in succeeding generations

Why pea plants? (2)

Influence their reproduction
Lots of offspring, fast

Did Mendel reject or except his initial hypothesis? Why?

Reject
It is reversible
Not always a blend

Medel's phenotype and genotype ratios for breeding of two hetero

pheno: 3:1
geno: 1:2:1

Why did Mendel cross a unknown parent with a homo-recessive plant to determine the unknown?

we have to give the recessive allele the chance to be shown

Mendel's laws

law of segregation
law of independent assortment

Law of segregation

when any individuals produce gametes, the two copies of a gene separate so that each gamete receives only one copy

Law of independent assortment

alleles of different genes assort independently of one another during gamete formation

mitosis vs. meiosis

mitosis: normal cell division
meiosis: crossovers and gamete formation

Due to independent assortment how many different gametes can a single human produce? (we have 23 chromosomes)

2^23

Steps for Inheritance problems

1) What are the pheno and genotypes of each parent?
2) What gamete(s) can each produce?
3) Draw Punnett square
4) Determine the phenotype of each offspring genotype
5) Calculate expected ratios or percentages of offspring geno and phenotypes

Types of dominance

complete
incomplete
codominance

Complete dominance

a single dominant allele produces the dominant phenotype (masks the recessive)

Incomplete dominance

the heterozygote phenotype is intermediate between the two homozygous phenotypes (blended)

Codominance

the heterozygote shows both the homozygous phenotypes

If you want the most incomplete dominance offsprings what combination of parents should you breed?

homozygous dominant and homozygous recessive

pedigree

A diagram that shows the occurrence of a genetic trait in several generations of a family.

What to be careful of when looking at a pedigree

pheno vs genotype

How does meiosis contradict Medel's law of independence

Meiosis indicates that entire chromosomes (with hundreds of thousands of genes) are inherited as a single unit

Which is correct? Law of independence or meiosis?

When recombination and crossovers occur (chromosomes are next to each other) then it is independent but when they do not crossover, they are dependent (they are both right and wrong)

The farther apart genes are the \________ they will recombine

more likely (because if they're very close the chromosomes have to crossover in a specific area)

Morgan and linkage: hypothesis and results

researched flies and two traits
Hypothesis: the two traits will be inherited independently (all phenotypes would be 1/4)
Results: genes didn't assort independently, but are linked (on the same chromosome)

Why did Morgan's flies have different proportions of phenotypes than expected?

Some of the traits recombined and some did not

How often does recombination produce gametes with chromosomes different than the parent's chromosome?

recombinants/total offspring

Linkage mapping

recombination frequency for many genes lets us map each genes location on the chromosome.

What to look for in terms of frequency/proportions for linked traits in a homozygous and heterozygous breeding?

If the traits are not as expected (not evenly distributed).

Which phenotypes should be most common? (expected for linkage)

parental phenotypes

Which phenotypes should be least common? (expected for linkage)

the ones that require two crossovers

What does the least common phenotype for linkage mapping tell us? How?

which gene is in the middle. Look at the least common phenotype and see which gene is different than the other two (which one changes)

1% recombination \=

1 map unit

percent recombination \=

\# recombinant offspring/total \# offspring

How to calculate distance between linked traits?

1) ignore parental phenotypes
2) for a and b recombinant look at the ones where a and b are different
3) do the same for a and c
4) divide those values by total \# offspring
5) to determine the distance between the two outside traits (b and c) simply add the two other values together

Why doesn't the Y chromosome contain anything critical to life?

females don't have it so if it contained critical information females would not do so hot

Why can women be carriers of an x-linked trait and men cannot?

men have no other x chromosome to "cover" it

pedigree (which ones are male or females)

squares are usually males. if sex linked, the carriers will be female

How to write sex linked genotype?

X(subscript b)X(subscript B)

Why are x-linked diseases more common in men?

They only have one x chromosome which they inherit from their mothers but women have two x chromosomes which decreases the chance of being colorblind (must have 2 colorblind alleles)

A man who is color blind and woman who is a carrier have a color blind son. Which parent did he get it from? What about their color blind daughter?

Son - mom
Daughter - both

Pleiotropy

one gene affects multiple traits

Polygenic inheritance

One trait is controlled by many genes

Ex. of polygenic inheritance

skin color, eye color, wheat fruit color

environment can effect traits too (examples)

hydrangea and pH
body size and horn size

Quantitative traits

traits that show continuous variation (most traits, i.e.: height, intelligence, athleticism) Gene x environment

Epistasis

when multiple genes interact to determine the phenotype

Epistasis example

Labrador coat color: black shows complete dominance over brown but their is an extension gene that determines whether the pigment is expressed (homozygous recessive extension gene makes coat yellow no matter the Bb genes)

Labrador example genotypes

Black: must have B and E
Brown: must have homo bb and E
Yellow: must have ee

natural selection acts on \____

individuals (who survives, who reproduces)

populations evolve when there are \____

changes in allele frequencies
changes in mean and variance of traits

genotype frequencies

the proportion of individuals with a particular genotype in a population

allele frequencies

the proportion of a particular allele across all individuals, or in the gametes produced by those individuals

Fundamental question of HW equilibrium

Are genotype frequencies the same from one generation to the next?

Notation for HW

allele:
p\= dominant allele frequency
q\= recessive allele frequency
genotype:
p^2\= homo-dominant frequency
2pq \= heterozygous frequency
q^2 \= homo-recessive frequency

How to calculate genotype frequencies from genotypes (given)

x/100

How to calculate allele frequencies from genotypes (given)

((2 x \# of homozygous for allele) + (\# of heterozygous))/total \# alleles

(total \# alleles \= \# individuals x 2)

How to calculate genotype frequencies from allele frequencies

square p and q

Genotype frequencies might change from the initial generation to the next but if the population isn't evolving than \____

allele frequencies won't change

As long as allele frequencies remain the same and mating is random, genotype frequencies will \_____

remain the same across generations

Hardy-Weinberg equilibrium

In a non-evolving population, genotype and allele frequencies reach equilibrium after one generation and remain constant in subsequent generations

HW calculations for:
2 alleles
3 alleles
4 alleles

(p+q)^2\=p^2 + 2pq + q^2
(p + q + r)^2\= p^2 + 2pq + q^2 +2qr + r^2 + 2pr
(p + q + r + s)^2 ... etc

requirements for HW

no mutations
random mating
no natural selection
no genetic drift (large population size - nearly infinite)
no gene flow (no migration)

Why do we care about HW?

HW is our baseline expectation (null hypothesis)

How to determine in a population is in HW equilibrium

1) determine observed frequency of genotypes
2) calculate the allele frequency
3) calculate expected genotype frequency
4) compare expected to observed
5) if there are deviations, what evolutionary mechanism caused them? which HW assumption might have been violated?

Ancestral vs. later population: in HW

all assumptions are met leading to no change in allele or geno frequency

Ancestral vs. later population: mutation

mutation causes a change in one type of allele leading to a new genetic variant in the population

Ancestral vs. later population: migration (gene flow)

migrating individuals bring a new allele leading to in the immigration of a new allele in the population

Ancestral vs. later population: genetic drift

caused by imperfect sampling leading to the loss of rare alleles

Ancestral vs. later population: non-random mating

no predicted ancestral or future populations because individuals prefer mating with certain phenotypes. With inbreeding: increase in recessive alleles and decrease in heterozygosity

Ancestral vs. later population: natural selection

environmental factors favor alleles leading to an increase in those alleles

What is mutation?

accidental change in DNA

types of mutation

substitution
insertions and deletions
chromosomal rearrangement (unequal)

Are mutations good or bad?

both (it depends on the mutation and where it is)

examples of bad mutations

sickle cell: single substitution
CF: triple deletion

Effects of mutations (example)

lizards in NM (one substitution which makes makes the lizard white)

Mutations and evolution

you can use changes in organisms to try and determine when branching occurred (evolutionary relationships)

Migration (gene flow)

Transfer of alleles through movement of fertile individuals or their gametes

Genetic drift

chance events that cause allele frequencies to fluctuate unpredictably from one generation to the next, especially in small populations

Genetic drift (details - small vs. large pop.)

small population: a rare allele is easily lost "just by chance"
large populations: higher probability of the rare allele persisting in future generations

consequences of genetic drift (4 things)

loss of overall diversity (fixed/lost alleles)
increase in homozygosity
increase in harmful recessive conditions
increased susceptibility to future stressors

Examples of extreme genetic drift

founder effect
genetic bottlenecks

Founder effect

a new population is created with few a few individuals from the initial population (started a new population with very little genetic diversity)

Genetic bottlenecks

when population size is severely reduced due to environmental impacts (elephant seals)

Non-random mating

inbreeding
outbreeding

Inbreeding

mating between relatives with similar genotypes

outbreeding

mating between unrelated individuals with dissimilar genotypes

How to recognize inbreeding on an exam

reduced heterozygosity

Natural selection types (3)

stabilizing
directional
disruptive

Natural selection frequencies when dominant is beneficial

dominant-homo and hetero increaese rapidly