Bio 1108 - Unit 1

Slides based on lecture slides and textbook reading

Genes

DNA that code for phenotypes

Gene Expression

regulated and influenced by the environment

Alleles

genetic variants resulting from different DNA sequence (the variations of genes)

Diploid organisms

have 2 alleles for every gene (one from mom one from dad)

Genotype

All the alleles for a particular phenotype

Asexual reproducation results in…

identical offspring

• high degree of genotypic and phenotypic similarity

• Rare DNA mutations can occurs the change DNA sequence

In multicellular organisms, identical DNA is passed from

cell to cell

Sexual Reproduction results in…

offspring with unique recombination of DNA from the parents

• only mutations in sperm ot egg are passed on (not if mutation is only present in parent - somatic cells)

Mutations (non adaptive)

• ultimate source of new allels

• is how the S allele first appeared (sickle cell)

——

• rare (random) event →takes multiple generations to accumulate

  • rates vary among organisms

Recombination

• in sexually reproducing organisms → occurs during meiosis

• (pieces of DNA break and swap to make new combonations of alleles)

Recombination + independent assortment =

each gamete being genetically unique

gametes

sex cells. (like sperm and eggs)

alleles can change in frequency:

bc of phenotype, environment and chance

Gene pool

all the alleles present across all indivisuals in a population (considered hevily when thinking about the molecular definition of evolution)

Genotype frequency in a population =

Number of indivisuals that have a geneotype/number of indivisuals in population

allele frequencey =

number of copies of an allele in population gene pool/ number of copies of ALL alleles in the population gene pool

Evolution

change in the genetic make-up of a population over generations

Hardy-Weinberg

Mathematical null model → allele and genotype frequencies stay constant from generation to generation

• Evolution HAS occurred in a population the is NOT in Hardy-Weinberg Equilibrium

Requires:

No selection, large population, no genetic drift, no migration, no mutations, random mating

AA Aa aa - Genotypes

p² 2pq q² - Genotype frequencies → stay constant

p+q =1 - allele frequency

p² + 2pq + q² = 1 - genotype freq

DNA

genetic material that stores and helps transmit info needed by the cell

Phenotype

expressed physical trait from a genotype.

Sickle Cell anemia

Genotypes:

AA

AS

SS

Genetic drift

random change in allele frequency from generation to generation. Over multiple generation one allele will reach fixation in the population.

• effects are less extreme in larger populations

→ Can remove advantageous alleles from the gene pool

Nonrandom Mating

When indivisuals in a population choose their mate based on genotype. (NOT sexual selection)

• does not change allele frequencies

• changes genotype frequencies (redistribution of alleles)

  • inbreeding: ex. self-pollination in plants

Natural Selection

a mechanism from for evolution

to occur:

• Variation

• Heritability

• Competition

• Mortality

Evolution by Natural Selection

Differntial fitness + survuval and reproduction

Fitness

the relative contribution of an indivisual to the future gene pool

• increased chances of surviving to reproduce/contribute to the next generation

Natural Selction results in

indviduals with adaptations

• they have increased fitness in a specific environment context

• adaptations are heritable → traits become more common over time

Somatic mutations

Not passed down

Germ-line Mutations

passed down from sperm and egg

Positive Selection (single gene)

Natural selection for an allele = increase in frequecy

Negative Selection (single gene)

Natural selction against an elle = decrease in frequency

Balancing Selection (single gene)

favoring variation = multiple alleles maintained

Why is the S allele still present

bc the S allele is “selected” for in certain contexts → high malaria enviornments

• AS has a heterozygous advantage (has the sickle cell blood cells + regular blood cells)

Stablilizing Slection (not single gene traits)

slection against extreme phenotypes

Directional Selction (not single gene traits)

slection for phenotypes above or below the mean - against one extreme (shifts to one extreme)

Disruptive Selections (not single gene traits)

selection against intermediate phenotypes (pushes population to the two “extremes”)

2 peaks

Artifical Selection (form of directional)

Selection is decided by breeder not competition (plants and animals: dogs, farm crops, etc)

Extensive artifical selection results in domestication.

• very efficient compared to natural selection (competition)

• done with a goal in mind

Phenotype only matters when…

it results in passing on genetic material to future gene pools

Sexual Selection

(directional selection)

Intrasexual - competition between indivisuals of the same sex

Intersexual - indirect competition → one sex chooses members based on sex based phenotypic criteria (colorful male birds)

Bottleneck

Extreme (usually) temporary reduction in population size →may result in loss of genetic diversity (genetic drift)

Founder Effect

type of genetic drift - occurs when only a few individuals establish a new population

Migration

The movement of organisms in a population from one place to another. Causes gene flow

Gene Flow

The movement of alleles through interbreeding between members of two different population.

• populatios become geneticall similar over time

Inbreeding Depression

inbreeding + genetic drift

Reduction in fitness resulting from breeding among close relatives →causes homozygosity of harmful recessive mutations

Deleterious Mutations

changes that harm the organism’s survival and fitness by disrupting necessary proteins

• ex. Huntington’s, Cystic fibrosis

Advantages Mutations

changes that improve the organism’s fitness

“postive” based on environment

Neutral mutations

changes that neither improve or harm the organism’s fitness, → will not be under selection, changes in alleles frequencies are purely random

Hybridization (goes against “BSC”)

Some closely related species can “interbreed” and reproduce

• natural selection may act agaunst hybrids

• reproductive isolation is incomplete

• can sometimes result in new species forming

  • does NOT work with: asexual or extinct species

    • requires significant study of reproduction

The Biological Species Concept: (BSC)

2 organisms are different species if they are reproductively isolated (has some problems tho)

Morphospecies Concept

organisms that look alike are the same species

Ecological Species Concept

each species is defined by it’s unique ecological role

The Phylogenetic Species Concept (PSC)

all members of a species have desended from a common ancestor and share a common fate.

• useful for asexually reproducing species

BSC explixity ties to reproduction and gene flow:

• populations MUST be reproductively isolated to be considered separate sparate species

Pre-zygotic reproductive isolation

happens before fertilization

Post-zygotic reproductive isolation

happens after fertilization

Initial separation can result in

evolution, drving each population diverging until they are reproductively isolated

Natural selection does NOT

always leads to speciation

Speciation can occur with or without natural selection

Separated population can diverge via genetic drift with no role for natural selection.

allopatric speciation (2 types)

new species develops due to physical or geographic barrier that splits a population

over time the two populations will become genetically distinct from one anouther until speciation occurs

Dispersal (allopatric speciation)

Indivisuals colonize a new area

Vicariance (allopatric speciation)

Geographic barriers arises →a population splits into separate population

“taxa” →groupings of related organisms

should be monophyletic group or clade

monophyletic group

contains a single common ancestor

Polyphyletic group

opposite of mono

Taxonomy → in scientific naming

Life

Domain

Kingdom

Phylum

Class

Order

Family

Genus

Species

Sympactric Speciation

evolution of a new species from a shared ancestral species while both groups continue to live in the same geographic area.

• think: disruptive selection: creates differences without separating a population

Can be driven by hybridization: chromosome number can be different from either parent species → hybrids are reproductively different because of gamete incompatabilities.

Analogous grouping lead to polyhyletic groups

result of convergent evolution

Convergent evolution

when similar characteris appear in distantly related taxa due to similar selective pressure

• common and needs to accounted for when constructing phylogenies

homologous features

physical features or bone layouts in different species that share a common evolutionary ancestor

phylogenetic trees

hypothesis about the evolutionary history of species

shared derived characteristics

characteristics that are shared by all lineages of a particular monophyletic group, but are absent in their sister taxa of the group and in the most recent node they share

Changes in DNA

also constitute a character that can be used to build phylogenies