Bio 204 Module 4

Natural selection

when certain alleles are favored and therefore increase in frequency, while others are not and decrease in frequency
-produces an adaptation which increases fitness

Genetic drift

random changes in allele frequencies from one generation to another which impacts small populations

4 main evolutionary processes

1. Natural Selection

2. Genetic Drift

3. Gene Flow

4. Mutation

Founder effect

Implication of genetic drift where drift occurs due to population isolation (could be thru migration); diversity decreases

Bottleneck

Implication of genetic drift which is a loss in diversity due to rapid population decline

Gene flow

Movement of alleles between populations, and depending on the allele fitness/variation can increase or decrease

Immigrant

Gene flow: bring alleles into a population, increasing variation

Emigrant

Gene flow: removes alleles from a population, decreasing variation

Mutation

The random production of new alleles which increases genetic variation

Directional selection

peak shifts to either right or left being more or less favored

Stabilizing selection

peak narrows inward

Disruptive selection

only the extreme ends survive (two peaks at both extremes)

Biological species

When different species dont breed and dont produce offspring also known as reproductive isolation

Morphospecies

Morphologically distinct populations (physical trait differences)

Polymorphism

Same species, but different morphologies/physical traits

Characteristics of speciation

genetic isolation and genetic divergence

Genetic isolation

Absence of gene flow

Genetic divergence

Mutation, genetic drift, natural selection

Allopatry

geographic isolation

Sympatry

reproductive isolation without geographic isolation

Allopatric speciation

A geographic barrier which occurs either from rafting (creating distance) or vicariance

Vicariance

a physical barrier between populations which prevents travel or interbreeding

Rafting

The dispersal and colonization of a species- individuals disperse and colonize a new habitat and then go through genetic isolation and divergence

Sympatric speciation

reproductive barrier of species living in the same region, where nonrandom mating within a population causes genetic isolation and divergence

Temporal isolation

breeding at different times

Habitat isolation

breeding at different habitats

Behavioral isolation

different courtship displays

Mechanical isolation

incompatible reproductive structures

Gametic barrier

egg and sperm are incompatible

Post zygotic reproductive isolation

hybrid inviability: offspring die

hybrid sterility: offspring cannot reproduce

polyploidy

when two individuals with different numbers of chromosomes cannot reproduce; a sympatric speciation mechanism

autopolyploid

a cell that starts with 2n chromosomes and ends with 4n

allopolyploid

two cells with differing numbers of chromosomes to begin with

ring species

organisms of connected neighboring populations that can breed with those next to them, but the two end populations are too genetically distinct to interbreed with one another

Model systems

Organisms whose development patterns are of useful comparison to humans since they are highly conserved

Examples of model organisms for development

-echinoderms

-frogs

-fruit flies

-worms

-chickens

Cell division breakdown

1. Cleavage= cell division without growth

2. Cytokinesis= actin myosin ring pulls the plasma membrane inward, creating a cleavage furrow to divide the cell

Cell signaling

A signal molecule, known as the ligand, binds to the receptor to initiate a response

autocrine

cell targets itself

paracrine

cell targets a nearby cell

endocrine

cell targets a distant cell through the bloodstream

hydrophobic signaling molecules

-cannot enter the cell

-receptors are intracellular

-receptors are transcription factors once the ligand binds to it

hydrophilic signaling molecules

-cannot enter cells

-receptors are on the cell surface

-signal transduction cascade

Cell differentiation meaning

all differentiated cells contain the same DNA/genes, but what makes them different is their combination of regulatory transcription factors which are responsible for turning specific genes on and off

Types of cell differentiation

1.cytoplasmic determents for protostomes and invertebrates

2. induction for mammals

cytoplasmic determinants

the determinants are produced by the mothers gene and are unevenly distributed, creating a concentration of varying molecules or factors in different regions of the cytoplasm, which then get divided up in the daughter cells

epigenetics

changes in phenotype due to changes in gene use without changing DNA sequence; used to clone organisms using a donor-specified cell + egg

totipotency

cloning of organisms

chromatin remodeling

reorganizing histones to make DNA accessible

methylation

DNA and histones cause nucleosomes to be highly packed meaning transcription factors cannot bind and genes are not expressed

acetylation

loose packing of nucleosomes, allowing transcription factors to bind and genes to be expressed

metastatic

cells that move when they shouldn’t

gastrulation

development from a single layer to a complex multi layer structure

single layered development organism

blastula

multi germ layer

gastrula

layers in gastrulation

-ectoderm (outer)

-mesoderm (middle)

-endoderm (inner)

what is comprised in the mesoderm

skeleton, muscle, circulatory system

what is comprised in ectoderm

nervous sytem

neurulation

formation of the central nervous system (brain and spinal cord)

Steps of nuerulation

1. form the notochord

2. notochord induces the formation of the nervous system

3. formation and differentiation of somites

somite

clusters in the mesoderm which make up different parts the body such as skin layers or back muscles

neural crest cells

the precursor to bones and beaks

bicoid

a regulatory transcription factor that controls the development of the head and thorax in fruit flies, more specifically creates the anterior structure

morphogen

a substance whose non-uniform distribution governs the pattern of tissue development

mutant bicoid gene

no anterior structures created, and may have two posterior structures

maternal effect gene

bicoid- a recessive gene where the phenotype depends on the genotype of the mother and not of the organism itself

gap genes

define the general position of the head, thorax, and abdomen

pair-rule genes

demarcates the edges of individual segments

segment-polarity genes

mark the boundaries within the segments

hox genes

responsible for fruit fly body plan: the combination expressed in fruit fly bodily segments that determines segment identity, such as wings or antenna

homeotic mutation

when the pattern of hox genes are altered; transforms one structure into another such as legs instead of antennae

Bmp

a growth factor found in short deep beaks

CaM

a growth factor found in long shallow beaks

what are beaks made of

bone with a layer of keratin

what is a growth factor

a signaling molecule which binds to a receptor to initiate a change in gene expression