CHANGE OVER TIME
(Chapters 12, 15, & 16)
1. Millions of species alive today are only a small fraction of all species that ever
existed. Fossil records reveal that about 99% of ancient species are extinct.
2. Fossils are relics or impressions of ancient organisms & include skeletons,
shells, seeds, insects trapped in amber, imprints of organisms, organisms
frozen in ice (wooly mammoth), or trapped in tar pits (saber-toothed tiger).
3. Fossils provide a record of biodiversity, behavior, & environment of ancient life
on Earth. They provide evidence of how organisms have gradually changed or
evolved over time.
4. Other evidence of the history of species can be found in:
a) homologous structures are similar in different organisms (forelimbs of
penguins, human, crocodile, bat)
b) vestigial structures - body parts with no function in present-day
organisms but probably were useful to their ancestors (ostrich wings,
eyes of blind mole rats, human tailbone)
c) similarities in the embryo stage of development in fish, reptiles, birds, &
mammals
d) biochemical similarities in the DNA of different species is the best way
to establish relationship
e) physical factors, such as location of continents, determine where a
species can spread (marsupials in Australia)
5. Organisms evolve by means of natural selection (“survival of the fittest”). This
means that when there are changes in a specific environment, individuals with
traits best suited for these changes have a better chance of surviving &
reproducing to pass these desirable traits from generation to generation.
Extinction will occur when previous traits are no longer suited to the new
environment.
6. Brand new species are able to evolve in a process called speciation. This can
occur when a population experiences geographic isolation or a mutation in
genetic material that creates new traits in the offspring.
7. When individuals within a species develop new traits, it is due to changes in the
DNA of the individual & is called a mutation. This may involve an entire
chromosome or a single DNA nucleotide. A genetic mutation can be lethal &
cause death before birth. Some mutations result in phenotypes that are
beneficial to the organism.
a) germ cell mutations occur in sperm or egg & do not affect organism, but
may be passed to offspring
b) somatic mutations occur in body cells & do affect organism (cancer)
8. Mutations may be mistakes during DNA replication. Many are caused by
environmental factors called mutagens. (UV light, x-rays, tobacco, asbestos.
9. Chromosome mutations are changes in chromosome structure or number:
a) deletion – chromosomal breakage causes loss of a piece of chromosome &
all information carried by it (Angelman Syndrome, Cri du Chat)
b) inversion – chromosomal segment breaks off & then reattaches in reverse
orientation to the same chromosome (familial deafness)
c) translocation – chromosomal segment breaks off & reattaches to another
chromosome (chronic myelogenous leukemia)
d) nondisjunction – the failure of a pair of chromosomes to separate during
meiosis causing 1 gamete to receive an extra copy of a chromosome & the
other gamete to lack a chromosome entirely (Down’s Syndrome)
e) point mutations – the substitution, addition, or removal of a single
nucleotide within a codon
THE DOG BIT THE CAT
THE DOB ITT HEC AT
10. Species adaptations for survival develop over many generations – types of
adaptations include:
a) structural - help species build better homes, defend against predators,
find food, etc. (mole rat claws & large teeth, porcupine quills, rattlesnake
heat-sensitive pits, spider webs, frog’s bright colors warn of toxicity)
b) mimicry - enables a species to resemble another species (monarch/viceroy
butterflies, coral snake/banded king snake)
c) camouflage - enables species to blend with surroundings (tiger’s stripes,
walking stick, chameleon, octopus)
d) dormancy - temporary escape from unfavorable environments:
1) hibernation - bears, reptiles, & amphibians hide underground in
extreme cold of winter when food is scarce - body processes such as
heart rate slow down & their lack of activity conserves energy &
reduces their need for food
2) estivation toads & box turtles - hide underground during summer
heat when ponds dry up – some species of desert reptiles & insects
hide during heat of day & are active at night (nocturnal)
e) migration - seasonal travel to more favorable environment (hummingbirds,
robins, ducks, sea turtles, elk, whales, & monarch butterflies)