Genetics and Evolution Flashcards
Independent Assortment
these genes separate and recombine independently of one another, with every combo of alleles having the same likelihood of occurring
division of genes during meiosis is random and therefore no 2 gametes will have same combo of genetic info, all combos have equal chance
Law of Segregation
genes separate into distinct alleles during gamete formation
Monohybrid and dihybrid
purpose is to isolate and study traits
monohybrid: P generation is selected based on one particular trait, one parent has dominant trait and other has recessive
dihybrid: P generation is selected for 2 traits that differ bw parents
Pedigree Analysis
diagram of familial genetic history and traces inherited traits from one generation to next
circles-females
squares-males
homozygous dominant- filled in
heterozygous dominant- partially filled in
Linkage
genes close together on chromosome are more likely to be inherited together
not found close- not inherited together
Sex-Linked Inheritance
traits that differ bw males and females
located on sex chromosome
genes on Y chromosomes only expressed in males
Y chr is smaller and has fewer genes
X chromosome larger and found in males and females
- -males have one allele for every X gene so this is the trait that will be expressed regardless if dominant or recessive
- -females have 2 X chromosomes so the dominant allele will express itself for X linked traits
Multiple alleles, codominance, and incomplete dominance
- -many genes have multiple alleles
- -multiple alleles means higher genetic diversity, more complex rules of dominance, and more combos of phenotypes
- codominance: appearance of 2 dominant alleles, both dominant genes are expressed
- incomplete dominance: one allele is not completely dominant over the other
Polygenic inheritance, epistasis, and pleiotropy
polygenic: traits determined by multiple genes, observed in continuous variation
epistasis: one gene suppresses the expressed phenotype of another gene
- -these are not alleles for the same trait
- -phenotype expressed by one gene dependent on modifier gene that masks the trait
pleiotropy: one gene can have multiple effects, one gene influences many traits
Organelle Inheritance
within mitochondria or chloroplasts
passed from parent to offspring
primary type of organelle inheritance from extranuclear organelles is called uniparental inheritance bc comes from mother
- most common in eukaryotic animals that undergo sexual reproduction
- -most important is mitochondrial inheritance
- —-major energy producers
- —-genetic material within this replicates independently of the material within the nucleus
- —at fertilization the egg provides a copy of the mothers mitochondrial DNA and this is passed on to offspring
Changes in Chr #
euploidy: equal # of chromosomes that is exact multiple of the haploid number
monoploid: half the normal number of chromosomes
- -monoploid in adult state
- -plants and fungi, insects
- -sterile non reproducing
polyploid: more than 2 pairs of chromosomes
- -flowering plants: exist and reproduce at increasingly higher ploidy levels
- -humans with this, rare and lethal
nondisjunction: results in chromosome abnormalities, which is the failure of one or more chromosomes to fully separate
monosomy: nondisjunction results in loss of single chromosome
trisomy: chromosome is added
Turner syndrome: monosomy that does not result in death or miscarriage, when females are missing X chromosome
Down syndrome: excess genetic material on chromosome 21
Changes in Chr Sruct
deletion: section of chromosome is lost during cell division
duplication: sections are duplicated, occurs when homologous chromosomes exchange unequal amounts of info during recombination or DNA is copied onto incorrect strand (Huntington’s)
translocation: nonhomologous chromosomes exchange info within a cell, normal set of traits but can be infertile
inversion: section of chromosome breaks off, becomes inverted, and reattaches to same chromosome
- -not usually genetic abnormalities unless accompanied with duplication or deletion
Common Genetic Disorders
cystic fibrosis- autosomal recessive, deletion of protein producing material on CFTR gene
–inherited by having 2 parents as carriers of mutated gene
huntingtons: degenerative disease, breaks down nerve cells in brain, presents later in life
- -duplication of genetic material causing large amts of huntingtons protein
- -autosomal dominant
- -parents have 50% chance of passing it on
sickle cell anemia: autosomal recessive
- -beta globin substituted
- -red blood cells sickle shape
- -cells break easily, low blood counts as result
muscular dystrophy: degeneration of skeletal muscle tissue
- -mutation in gene that prevents proper production of dystrophin–builds and repairs muscle
- -gene defect on X chromosome therefore X linked recessive
PKU: gene defect leads to increased phenylalanine levels which is amino acid in proteins
- -autosomal recessive
- -mutation in PAH gene which prevents amino acid from breaking down
Tay-Sachs: degenerative nerve disease, destroys brain and spinal cord cells
- -autosomal recessive
- -mutation in HEXA gene which makes enzymes that break down and remove toxins
Albinism: lacks proper amt of melanin
- -autosomal recessive
- -others passed thru X chromosome
- -mutation in TYR gene
Polydactyly: extra fingers or toes
- -mutation in GL13 gene
- -autosomal recessive or dominant
Hemophilia: X linked recessive, primarily in males
–linked to deleted or defected gene that produces blood clotting protein
Red green color blindness: X linked, mutation in genes that produce proteins in the retina to detect certain colors
Mutation
- -can have no effect or be harmful
- -some can cause variation in traits
–DNA mutations in gametes are passed on
genetic variation is more complex in eukaryotes that undergo sexual reproduction
–asexually reproducing organisms make offspring by replicating exact copies of DNA from one parent, this limits genetic variation
Crossing Over
also called recombination
happens during meiosis
source of genetic variation among eukaryotes
is during prophase 1
Genetic Exchange
bacteria and archaebacteria (protozoa and algae) exchange genetic info by the 3 methods below:
- -which creates variation
- -these below allow them to make new DNA sequences
transduction: host bacterium is infected by a bacterial virus or phage, that absorbs genetic info from the host to its own genetic code
transformation: bacterium takes up DNA from a source oustide the cell, this exogenous DNA is absorbed thru the membrane, must be in a state of competence for this (sufficiently permeable to receive info)
conjugation: genetic exchange in bacteria that requires cell to cell contact
- -plasmids are exchanged over a connection bw 2 diff bacteria
- -plasmids are small extrachromosal DNA from within bacteria
- –these plasmids replciate independently from the DNA in a chromosome
- –conjugation begins when bacterium produces sex pilus
- -portion of DNA is transferred thru pilus
- -the genetic info transferred can recombine with the genetic info within that new cell (host)
Sexual Reproduction
division of genes during meiosis happens randomly and independently of gene division in other gametes
therefore no 2 gametes will contain the exact same combo of genetic info and all combos of genetic info have an equal chance of occurring
Distrib and Mvmnt of Alleles w/in Pop
genetic drift: changes to allele distribution within pop
- -variation in gene frequency, accounts for random nature in which traits are passed on
- -affects small pop
- -exposed to natural disaster or disease
nonrandom mating: probability of 2 members of a pop. will mate is not equal to others in pop.
sexual selection (form of nonrandom mating): choose mates based on advantageous characteristics
Distrib and Mvmnt of Alleles bw Pop
gene flow: movement of alleles from one pop to another via migration
- -can introduce new alleles and gene combos
- -increases genetic diversity
- -alters frequency of alleles
Conditions of HW equilibrium
- pop large in size and no genetic drift
- isolated pop., no immigration or emigration
- no genetic mutations
- mating is random
- no natural selection
Calculating allele frequencies using HW equation
genotype: p2+2pq+q2=1
- p is dominant allele
- q is recessive allele
- p2: frequency of homozygous dominant
q2: frequency of homozygous recessive
2pq: frequency of heterozygous
sum of p and q must equal 1
p+q=1 : allele frequency in a pop.
==totals are divided by the total number of alleles
Natural and Artificial Selection
natural selection: members of a pop. best adapted to environment survive and reproduce (fitness)
–favorable traits passed on
4 basic conditions for nat selection to occur:
- -inherited variation
- -overproduction of offspring
- -fitness to environment
- -differential reproduction
differential reproduction: biologically fit animals alter gene pool of pop. so not all membranes reproduce at same rate
Artificial selection: intentionally breed organisms with the same desirable traits thru selective breeding
Sexual Selection
intersexual reproduction: select mates based on visual cues
Genetic Drift
does not involve survival of fittest, is random
alters alleles and traits in gene pool
can happen due to humans, disease, or natural disasters
bottleneck effect: survival is random, results in less genetic diversity, descendants of same small population and genetically similar
founder effect: small pop. becomes isolated from large pop. thru migration
–small pop has led genetic diversity
Coevolution
–evolution of one organism affects that of another
–typically happens bw those that have close
–interdependent ecological relationship
also predator prey likely to evolve together
competition drives evolution
- -occurs when 2 species share niche (space and role) and compete for same limited resource
- -one species will become extinct
mutualism: both species benefit
Adaptive Radiation
- -rapid diversification of gene pool when the species is introduced to new environments
- -leads to new species coming from original pop.
- -each of new pop. of species distinguished by different adaptations to environment
Molecular Evidence
DNA, RNA and proteins found at molecular level are profoundly similar across groups of living organisms
- -structural similarity is known as homology which means they share common ancestry
- -genetic code same for all organisms but structures of DNA sequences vary from sp to sp
Structural and Developmental Evidence
comparative anatomy: similarities and diff in anatomy of diff organisms
– share same basic structure, connected to skeleton or other body parts similarly, and develop in embryonic stage similarly (example: presence of notochord)
Fossil Record
fossil- remnant or impression of early life form perserved in rock
- -can form thru permineralization or casting/molding
- -rare occurence
form in sedimentary rock- formed by layers of sediment depositing on top of another
- -layers act as marker of geologic time
- -layers (strata), studying this is called stratigraphy
- -stratigraphy governed by law of superposition which means top layers are younger and bottom ones are older
- -this law doesnt always apply due to earthquakes, plate movement, volcanic eruptions
- fossils in same layer prob related
radiometric dating: determines age of rocks by measuring rate of decay of radioactive elements in rock
Endosymbiosis
- -first organisms were prokaryotic and eukaryotes came from them
- theory states mitochondria and chloroplasts originated as free living bacteria billions of years ago
- -theory suggests bacteria took up residence in other bacteria, the mitochondria used oxygen of host cell and host received energy
- -over time genetic info came together and the 2 species became one
- -theory is supported by fact that mitochondria and chloroplasts lack cell membrane, reproduce via binary fission, and have circular genomes
- -also lineage that would evolve into plants experienced endosymbiosis with another form of bacteria and became the choroplasts
Convergent vs Divergent Evolution
convergent evolution: 2 unrelated species face similar environments and may evolve similar trait or behavior (analogous structures)
divergent evolution: 2 or more species descend from a common ancestor but evolve dissimilar traits
- -structures differ in appearance and function
- -genetically similar species
Major Evolutionary Trends
–refers to change to trait or structure that occurs in one lineage or across lineages of several groups of organisms
–trends are directional, consistently appear in greater frequency throughout lineage
- -persistent and result in significant change over time
- -can affect one species or be widespread
- -multicellularity: differentiates plants, animals, and fungi from bacteria, protists, and archaebacteria (unicellular)
- -multicellularity: leads to great diversity, these organisms evolved from unicellular ones
- -unicellular means those 3 perform all life functions within single cell
head formation (cephalization): begeins with advent of multicellular nervous tissue (has specialized cells called neurons)
- -cephalization: tendency of nervous tissue to become concentrated at anterior end of organism during embryonic development and this concentrated tissue becomes head
- -bilateral symmetry: cephalization occurs among organisms that display this, this means to have 2 identical sides with distinct head and tail end)
- -larger the mass of nervous tissue the more advanced the organism
Reproductive Isolation
- -no gene flow due to isolation
- -isolated pop may undergo structural or behavioral changes, makes inbreeding no longer possible
prezygotic isolation: occur before gametes are formed thru fertilization, prevents parents from making offspring
–includes the following
=habitat isolation: keeps 2 pop isolated bc their needs are met in diff geographic areas (geographic barriers)
=temporal: organisms only able to reproduce within short window of time
=behavioral: tendencies of certain sp to select a mate for interbreeding, mating rituals and displays (calls or pheromones)
=mechanical: prevent formation of gametes even if they mate, structural changes to the reproductive organs
=gamete: prevents eggs and sperm from coming together even if they are compatible
- -occur among sp that do external fertilization
- -sperm and egg meet but cant fuse
Post zygotic
- after 2 sp have mated and reproduced
- -hybrid: unlikely to survive and reproduce
- -since genetic info is from 2 diff sp they do not have full set of chr that are compatible with one another
- -hybrid infertility
Types of Speciation
—diff pop of same species face diff environments and acquire different adaptations, this results in speciation (single species into two or more distinct species)
speciation: pop. of organisms becoming genetically distinct from parent species which can lead to reproductive isolation or reduction of gene flow
allopatric speciation: result of geographic isolation, physical barriers prevent movement or migration, can occur due to natural events
peripatric speciation: one of the separated pop is very small in number, genetc drift affects this pop.
–separated pop physically isolated from larger one and can become new incompatible species
parapatric speciation: not a result of physical barrier. isolated bc they only mate and reproduce with individuals in immediate area
–can happen bw pop that occupy different niches in same habitat
sympatric speciation: no isolation bw pops, no physical barriers, no habitat isolation
- -occur as result of reproductive isolation mechanisms such as behavior, temporal, or mechanical
- -pops in same habitat may reproduce at diff times or respond to diff mating behaviors
- -reduced gene flow, lead to speciation
Gradualism
gradualism: evolution occurs as a result of small changes accumulated over long period of time
- -transitional fossils support this
- -these fossils are missing link bw traits in ancestral groups and descendants
Punctuated Equilibrium
punctuated equilibrium: species unchanged for long periods of time, species in stasis (long period of inactive equilibrium), experience evolution and speciation in short bursts of time
Panspermia
- -life on Earth was seeded by organic cmpds and microscopic life found in outer space
- -cmpds and organisms arrived via meteors
- -known as asteroid seeding
- -believe organic cmpds (contain C) building block of life arrived via meteors
- –examples: lipids, carbs, amino acids
- -also believed life arrived in the form of dormant bacterial spores from meteors or comets rather than life being built from organic cmpds that arrived this way
Abiotic Synthesis of Org Cmpds
–Miller-Urey Experiment: based on theoretical model of chemical evolution that hypothesizes that org. molecules of life formed from inorganic cmpds during atmospheric reduction on Earth which resulted in atmosphere with limited oxygen
- -they made simulation of Earths atmosphere back then
- -simulation was gas mixture and was exposed to heat and electricity
- -gave rise to org. cmpds
- -provided evidence that org. cmpds can arise abiotically
- -they used mixture of various gases that should have been present back then (includes methane, water, ammonia, and hydrogen)
- -recent evidence showed volcanic activity then, and therefore inorganic cmpds like nitrogen and CO2
- -creation of org materials from non living matter has not led to how these building blocks of life came together and formed life
Biological Influences on Atmospheric Composition
- -4 billion yrs ago first life forms much different than now bc atmosphere was different
- -Earth was undergoing extreme volcanism releasing CO2, sulfur dioxide, and nitrogen
- -life was mostly microbes
- -2.5 billion years ago first photosynthetic organisms (blue green algae)
- -took billions of years for oxygen to emerge as major component of atmopshere
- -1.8 bya oxygen was built up and the evolution of life was rapid
- primitive life forms replaced by oxygen tolerant sp
- oxygen driving force of evolution and led to larger more complex organisms
Development of Self Replication
- -believed proteins were the first to evolve self replication
- -RNA now believed to potentially be precursor to all life on Earth
- -RNA unique bc can carry out fns of both DNA and proteins
- –can store genetic info and act as catalyst
- –potentially self replicate
- –existed among early life
- -believed RNA was causing chemical rxns to drive photosynthesis, respiration, metabolism. etc
- –RNA was store and replicating genetic info
- -proteins and DNA evolved to take over and specialize in these fns
Lack of Genetic Diversity
leads to sharp decline in numbers
less likely to adapt to outside influences
small gene pool can lead to interbreeding
interbreeding leads to inc of less desirable or harmful genes
negative impact on species fertility and fitness
Environmental Pressures
- -lead to pop decline, loss of genetic diversity, extinction
- -habitat change
- natural factors: fire, drought, flood
- organisms must travel to suitable habitat or adapt
–habitat change can lead to habitat destruction: complete loss of biological fns, pop becomes fragmented and unable to reproduce, lowers genetic diversity, pop. vulnerable to environmental change
- -climate change: lead to sp loss or extinction
- -global warming: causes habitat loss in cold climates, alters vegetation, flooding
Human Impacts
agriculture and food production
leads to habitat loss and fragmentation
overharvesting of plant and animal sp
more industrialization means more environmental degradation which occurs as result of extraction of fossil fuels and pollutants contaminate air, water and land
human caused climate change due to CO2 emissions from burning of fossil fuels, this leads to inc impact of greenhouse effect
—-greenhouse effect is natural and has been amplified causing Earth temp to rise as more heat is retained
Interspecific Competition
- -humans move and bring new sp
- -non native sp introduced and wreak havoc on natives
- -new sp competing with native species in same habitat is interspecific comp.
- -if non native more successful, natives will decline and go extinct
