11.1 - changing allele frequencies

variation in traits and genes in a population can be influenced by

many factors and changes over time

gene

sequence of DNA that codes for a specific characteristic or trait

slight variations in gene can result in

different forms of trait (alleles)

alleles

variations of genes

various combinations of alleles in individual make up its..

genotype

genotype + environment determines organism’s…

phenotype - observable characteristics of organism

genetic diversity/genetic variation

variation in genes or alleles within population or species

gene pool

total genetic diversity in population

* all dem alleles

allele frequencies within a gene pool….

change over time

4 main processes that contribute to evolution

* mutation
* natural selection
* gene flow
* genetic drift

allele frequency

relative proportion of particular allele in population

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homozygotes will have ___ copy

heterozygotes will have ___ copy

* homozygotes → 2 copies of allel
* heterozygotes → 1 copy of allele

all genetic diversity between species & individuals of the same species is a result of…

mutation

define mutations

changes in DNA which are the source of new alleles in a species or population

* can have a beneficial or harmful effect, or no effect at all
* change to DNA composition of a cell or organism that generally results in changed phenotype

2 types of mutations

* gene point mutation
* chromosome mutation/abnormality

gene mutation

random change in base sequence within a specific gene generally resulting in a changed phenotype

2 types of gene mutations

* substitution
* silent - affected codon still codes for same amino acid
* missense - codes for different amino acid
* nonsense - changes to stop codon, truncating protein
* frameshift
* insertion
* deletion

chromomal/block mutations

• affects structure of chromosomes

• result of errors in meiosis

• leads to sgnificant changes in genes

types of block mutations

• duplication: gene sequence repeated

• inversion: chromosome segment breaks off, flips around backwards and reattaches

• deletion: due to breakage, piece of chromsome lost

• translocation: involves 2 chromosomes that aren’t homologous where part of 1 chromosome is transferred to another chromosome

chromosomal abnormalities

involve addition or absence of an entire chromsome

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aneuploidy

addition or absence of a chromsome

polyploidy

addition of entire sets of chromsomes

what are mutagons + give examples

factors that induce mutations

* different forms of radiation → UV radiation can cause mutations in skin cells that results in skin cancer

somatic mutations

occur in body cells & only affect that individual

germline mutations

are heritable as they impact gametes (sperm & egg cells) & can be passed to offspring

* may bring new allele in gene pool, potentially influencing allele frequencies

what is natural selection

applies when selective agent removes unsuited individuals from the population. suitable phenotypes survive and then breed and have offspring, increasing those alleles in each generation

• genetic diversity between individuals in a populations results from different phenotypes (traits) having varying advantages for survival and reproduction

• individuals well suited to their environment are more likely to survive & reproduce

the alleles that survive and reproduce will..

persist in population & increase in frequency

what is selection pressures

an environmental factor that affects the survival & reproductive successes of an individual based on their phenotype

2 types of selection pressures

* natural environmental pressures
* artificial pressures brought about by humans through selective breeding

examples of selection pressures

* climactic conditions → extreme temp changes, drought
* competition for resources → food & water, competition for shelter
* mate availability
* predator abundance

high adaptive value

some phenotypes have a high adaptive value → give organism advantage over individuals with phenotypes of low adaptive value

* individual is more likely to survive to reproduce & pass alleles to next generation

adaptations

traits that are well suited to an organism’s environment

gene flow

transfer of alleles between populations & can result in changes in allele frequencies in gene pool

* individuals from different populations interbreed
* individuals enter (immigration) or leave (emmigration) a population
* results in new alleles being introduced or lost, increasing or decreasing genetic diversity of population

genetic drift

random change in allele frequencies due to chance events (births, deaths, natural disasters)

why is a reduced genetic diversity bad?

• inbreeding: keeps harmful genes in gene pool

• lower adaptive potential - populations become vulnerable to new selection pressures that could challenge or wip out entire population due to absence of advantageous alleles

2 types of genetic drift

* population bottleneck
* founder effect

population bottle neck

drastic reduction in population due to random chance event

* ex) natural disaster, human activities (hunting, land clearance)

what happens in bottleneck

* reduced population size → possible reproductive pairings are limited, leading to inbreeding
* inbreeding results in reduced genetic diversity in population & increase in numbers of homozygous individuals
* vulnerable to environmental change & dying out

high & low level of genetic diversity reaction to change

* high level of genetic diversity → populations adapt to new or changing environment
* low level of genetic diversity → species or populations go through genetic bottleneck, increasing risk of extinction

founder effect

occurs when a small group of individuals is genetically isolated from larger population, either by migration, geographic barriers or habitat fragmentation

what happens in founder effect

* small portion of alleles of original population & therefore lower genetic diversity
* increased inbreeding & loss of alleles due to genetic drift

natural selection theory

1. born with pre-existing genetic variation
2. selection pressure
3. selective disadvantage


1. won’t survive until reproduction - alleles won’t be passed down to next gen
2. allele frequency decreases - no reproduction
4. selective advantage


1. can access food & survive until reproduction
2. can produce viable, fertile offspring
3. allele frequency increases