Gerhart Bis 2B Midterm 2

BIS 2B Midterm 2 for Gerhart - Winter 2025

Microevolution

Changes in allele frequencies across generations; small scale changes over short time

Macroevolution

Accumulation of microevolutionary changes that a new species arises; large scale changes over time frames

Natural Selection

Increased survival and reproduction of some individuals based on their phenotypes

Variation

Varity in traits/phenotype; 1 of the necessary and sufficient conditions for natural selection

Heritability

trait is partially genetic/is able to be passed onto their offspring; 1 of the necessary and sufficient conditions for natural selection

Differential Success

individuals w/ different traits differ in their survival and fitness; 1 of the necessary and sufficient conditions for natural selection

Drivers for natural selection

Species interactions, environmental factors, mate choice

Sexual selection

Selection for traits that enhance reproductive success (even if costly to survival)

Intra-sexual selection

Individuals of the same sex fight for right to mate with other sex

Inter-sexual selection

mate choice, one sex is choosey and chooses based on specific phenotypes regardless of benefits

Altruism

a behavior that reduced individual relative fitness and increases fitness of others

ex.) ground squirrel alarm call: alarm species but risk their own life

Kin selection

selection that favors behaviors that increase relatives reproductive success

Inclusive fitness

the sum of an individuals own fitness and its contribution to the fitness of relatives

Directional selection

phenotypes at one extreme have the highest fitness, mean trends toward that extreme

Stabilizing selection

average phenotype has highest fitness, the mean stays the same but variation is reduced

Disruptive selection

phenotypes at both extremes have higher fitness than the mean, variation increased and bimodal pattern emerges

Positive frequency dependence

the most common phenotype is most benefitted

Negative frequency dependence

that rarest phenotype is most benefitted

Balancing selection: spatial variation

each region has its own more common phenotype to adapt to its environment

Balancing selection: temporal variation

phenotypes adapting to time

ex.) climate change making plants adapt to the rise in temperature

Constraints of Natural selection

Environmental change: depends when/where organism exists

Law of Physics: efficiency of diffusion of oxygen determines body size

Evolution History: ancestors determine phenotypes

Trade Offs: can only maximize one trait, limiting the others (ex. big size, small amount of offspring)

Lack of gene variation: phenotypes can’t be created by natural selection, only work with what’s given

In the equation R=h²S, what does the R mean

Response to selection, found by subtracting the parent mean - offspring mean

In the equation R=h²S, what does the h² mean

Heritability, found by dividing R/S = h²

In the equation R=h²S, what does the S mean

Strength of selection, found by subtracting the new mean (breeder or surviving mean)- original population mean

Diploid

2n (ex. 46 chromosomes)

Haploid

1n (ex. 23 chromosomes, half of original)

Transcription

DNA to RNA (occurs in nucleus)

Translation

RNA to Protein (occurs in cytoplasm w/tRNA)

mRNA strand

Same as sense strand but T’s are replaced with U’s

Simple mutations

All mutations cause genetic variation

Substitution mutation

One or more nucleotides are exchanges, impactful if early stop codon

Insertion mutation

one or more codons are added

Deletion mutation

one or more codons are deleted

Allele

A single version of a gene (B = brown, b = blue)

Genotype

Combination of alleles (ex. Bb, BB, bb)

Law of Segregation

When any individual produces gametes, the two copies of a gene separate so that each gamete receives only one copy; Mendel’s Laws

Law of Independent Assortment

Alleles of different genes assort independently of one another during gamete formation; Mendel’s Laws

Simple/Complete Dominants

A single dominant allele produces dominant phenotype

(Bb, and BB = purple flower because of B being dominant)

Incomplete Dominance

The heterozygote phenotype is combination of two homozygous phenotype

(BB = purple, bb = white, Bb = lavender)

Co-Dominance

The heterozygote phenotype is both the homozygous phenotypes are expressed fully

(BB = Purple, bb = white, Bb = purple and white splotches)

Pleiotropy

One gene affects multiple characteristics

ex.) coat color and blue eyes also affects deafness

Polygenic Inheritance

Multiple genes contribute to same trait (additively)

ex.) more dominant alleles = darker the color gets

Environmental Influences

environment affects the phenotype

ex.) Color in hydrangeas is affected by pH in soil

Epistasis

when multiple genes interact to determine phenotype, one hides the trait of another

ex.) black/brown gene: black is dominant over brown, extension gene: recessive trait lacks pigment (yellow)

Importance of genetic diversity

maintain a healthy population and response to new environmental pressures

Sexual reproduction

shuffles whole genomes of two individuals

Recombination

shuffles alleles on a given chromosome, creates new chromosome combinations different than what the organism inherited

Linked genes

Closer 2 genes are on chromosome = more likely to be inherited together and less likely to be separated by recombination therefore frequency of gametes aren’t even

Unlinked genes

Expect to follow law of independent assortment and all offspring have equal frequency of gametes

Hardy-Weinberg Equilibrium

Allele and genotype frequency won’t change IF

1. No genetic drift (random shifts of allele frequency)

2. No natural selection occurs

3. No migration occurs (individuals mating with different populations i.e. Alaska moose mating with moose from Maine)

4. No mutation occurs

5. AND random mating does occur

Violating any = evolution is occurring

Shortcut for finding heterozygous genotype frequency

2 * allele 1 * allele 2; 2pq

Shortcut for finding homozygous genotype frequency

allele² (ex. p² or q²)

Equation for finding one allele frequency in heterozygous pairs

Half the observed number of Xx then add to homozygous pair and divide by total of population

Ex:) SS = 30 Ss= 30 ss = 50

F(S) = 30+ (30/2) =45/110 =0.409

Inbreeding

Preference for similar genotype or phenotypes; reduces heterozygosity

Outbreeding

Preference for different genotypes or phenotypes; increases heterozygosity

The Founder Effect

A new population is created from a few individuals from the initial population; reduce gene pool but original population still exists and can maintain diversity

Genetic Bottlenecks

When a specific total population size is severely reduced; the small population is all the remains and whatever genetic diversity left remains

Consequences of genetic drift

1. Loss in genetic diversity

2. Increase in homozygosity (inbreeding)

3. Increase in deleterious recessive conditions

4. Increase in susceptibility

The Biological Species Concept

A species is a group of potentially interbreeding natural populations that are reproductively isolated from other groups

ex.) horse + donkey = infertile mule

Limits: extinct animals, asexual organisms

The Lineage/Phylogenetic Species Concept

A species is a group of individuales that share evolutionary history and genetic relatedness

ex.) phylogenetic tree sharing a branch

Limits: needs a lot of genetic data

Morphological Species Concept

A species is a group of individuals that share morphological similarity are the same species

Ex.) characterizes on features like body shape

Limits: analogous traits ruin this concept such as birds and bats have wings, fish and penguins have fins

Analogous traits

Similar in different organisms because of similar hábitat or natural selection

Ex.) dolphins and sharks (ones a mammal and ones a fish but both have the same coloring and body shape)

Homologous traits

Similar in different organisms because inherited from common ancestor

Ex.) Amnion (membrane that covers offspring embryo) trait passing to mammals, lizards and snakes, crocodiles, ostriches, and hawks/birds

Prezygotic barriers

Prevent mating or prevent fertilization if mating occurs

Prezygotic Habitat Isolation

No contact, different habitat

(Ex. Lions and tigers living in different parts of the world)

Prezygotic Temporal Isolation

Different breeding times

Ex.) coral releasing gametes at different times

Prezygotic Behavioral Isolation

Dont recognize eachother as possible mates

Ex.) birds having different songs to appeal to only their species

Prezygotic Mechanical Isolation

Physical difference = no mating

Ex.) reproductive organs arent compatible

Prezygotic Gametic Isolation

Sperm cant fertilize egg

Ex.) sperms having different proteins attached where they can’t get into the egg and fertilize

Postzygotic Barriers

Prevent a hybrid zygote from developing into fertile adult

Postzygotic Reduced Hybrid Viability

Hybrid offspring don’t fully develop or have low survival

Postzygotic Reduced Hybrid Fertility

Hybrid offspring are viable but can’t reproduce

Ex.) mules having odd # chromosomes makes the infertile

Postzygotic Hybrid Breakdown

Hybrid offspring viable and fertile but the following generation inviable or sterile

Allopatric

Fully seperated population

Sympatric

Fully connected population

Allopatry through Vicariance (geographical seperation)

Population split about equally for a long time because of a land mass or barrier. Over time they begin to differ because of mutations, genetic drift, mutations, and selection. They become so different they are considered two different species.

Allopatry through the founder effect

A small group of the population colonizes a new area, seperating from the larger population. Over time differences in mutations, selection, drift etc cause formation of new species. Reproductive barriers are then formed and then considered seperate species.

Speciation through sympatry

Genetic change arises in a couple individuals that distribute through the population. Eventually a reproductive barrier is created and two species are formed.

Ex) flies preferring to breed on the same fruit tree their parents did

Monophyletic

A group of organisms that have a common ancestor AND all its descendants