selection and evolution

witerally need to pass this for pookie bear brown

what does sexual reproduction produce?

genetic variation among the individuals in a population

what is genetic variation caused by

• independent assortment of chromosomes during MEIOSIS

• crossing over between chromatids of homologous chromosomes

• random mating (same species)

• random fertilization of gametes

• mutation

when do mutations occur?

if a mistake occurs in DNA replication

what do mutations produce?

completely new alleles

what type of cells do mutations produce?

somatic cells and cells found in ovaries and testes

mutations in somatic cells

• no effect on organism

• cant be passed down via sexual reproduction

mutations in ovary or teste cell

• can be inherited by offspring

• mutated cell can form a gamete (will contain mutation)

genetic variation

differences in the DNA among a population

variation in environment

NOT passed down

discontinuous variation

• qualitive differences, fall into distinct categories (ex: blood groups)

• different alleles at a single locus have LARGE effects on the phenotype

• different genes = different effects

continuous variation

• quantitative differences with a range between extremes (ex: height)

• different alleles at a single locus have SMALL effects on phenotype

• different genes = same effect

• may have polygenes

polygene

many genes have combined effect on a particular phenotypic trait

environmental facts that affect gene expression

diet, temperature, oxygen levels, humidity, light cycles, presence of mutagens

natural selection

effects of selection pressures on frequency of alleles in a population (organisms that are more adapted = more likely to survive & reproduce)

survival

live long enough to reproduce and pass genetics to next generation

fitness

how well an organism can survive in its environment

selection pressure

causes or events in nature that will increase or decrease the chances of alleles being passed on

environmental factors of selection pressure can be

biotic or abiotic

biotic

living aspects of environment (predators, competition for food, water, mates, or shelter)

abiotic

non living aspects of environment (natural disasters, availability of resources, human interference, temperature, sunlight)

evolution

change in heritable characteristics of populations over many generations, passed on through reproduction

3 ways natural selection can affect genetic drift in a population

stabilizing, directional, disruptive

stabilizing selection

genetic diversity decreases as population stabilizes on a specific trait that is neutral

directional selection

conditions favor individuals with extreme traits or reproduce more on ONE side (triggered by change in environment or intro of new alleles)

disruptive selection

conditions favor both extremes within a population, acts against neutral phenotypes (triggered by change in environment or intro of new alleles)

hardy weinberg equilibrium

used to compare allele frequencies in a given population over a period of time (never fr occurs)

rules for equilibrium

1. no gene mutations

2. no migration

3. random mating MUST occur

4. no genetic drift

5. no natural selection

artificial selection

the intentional selection pressure on an organism by humans for specific characteristics (controlled by humans)

selective breeding

individuals showing one or more of these desired features to a larger degree than others chose for breeding

darwin wallace theory of evolution observations

1. organisms produce more offspring than needed to replace parents

2. natural populations tend to remain stable in size over long periods

3. variation among individuals of one species

theory deductions

1. competition for survival

2. best adapted variants will be selected for (natural selection will occur)

speciation

how new species arise

reproductive isolation (prezygotic)

• individuals don’t recognize each other as potential mates

• animals physically unable to mate

• male gamete unable to fuse w female gamete

reproductive isolation (postzygotic)

• failure of cell division in zygote

• nonviable offspring

• viable but sterile offspring

allopatric speciation

when 2 populations are separated from each other geographically

geographical barriers

mountains, bodies of water

sympatric speciation

2 populations living together separate from each other

(occurs through polyploidy)

polyploidy

organism with MORE than two complete sets of chromosomes

when does polyploidy happen

incomplete division of chromosomes during meiosis

are polyploidy organism considered a separate species from parent?

yes because they cannot reproduce with them

tetraploid

• organisms with 4 sets of chromosomes

• sterile

• can reproduce asexually

• common in plants, rare in animals

how does a tetraploid form?

during meiosis the 4 sets of chromosomes all try to pair up and can’t divide properly

triploid

• organisms with 3 sets of chromosomes

• sterile (cant split 3 sets)

• can reproduce asexually

how does a triploid form

diploid gamete and haploid gamete fuse to form a triploid

autopolyploid

• 4 sets of chromosomes from same species

• sterile

allopolyploid

• 2 sets of chromosomes from 1 species, and 2 from another

• fertile (can’t mate with parent species)

2 methods of comparison between species

• comparing amino acid sequences of proteins

• comparing nucleotide sequences of mitochondrial dna