Heritable Traits and Evolution

• Species change over time through evolution, but these changes must be heritable.
• Acquired characteristics develop during an individual's lifetime and occur in somatic cells.
• Heritable characteristics must occur in gametic cells, such as sperm and eggs.

Mechanisms for Heritable Changes

• Crossing over
• Independent assortment
• Fusion of gametes
• Mutations

Mutation

• The only mechanism of variation for single-celled organisms (silent mutations count).

Crossing Over

• Occurs during prophase of meiosis.

Independent Assortment

• Occurs during metaphase 1 of meiosis.

Fusion of Gametes

• Creates new combinations of alleles.
• LUCA: Last Universal Common Ancestor.

Fossils and Radioactive Dating

• Fossils found in various layers were different, allowing for a sequence of events to be deduced.
• Radioactive dating, such as with Carbon-14 (C14), calculates the age of rocks and fossils.

Carbon Dating

• C12 is the majority of elements.
• C14 is an unstable/radioactive form with 6 protons, 6 electrons, and 8 neutrons.
• C14 decays, emits energy in the form of radiation until the nucleosis is stable (C14 -> N14).
• Carbon is used in dating because it is ingested by living organisms via carbon compounds.
• In C14, Nitrogen 14 (N14) has 7 protons and 7 neutrons, but it is unstable.
• The extra neutron pushes into N14, causing it to lose a proton and become C14.
• When an animal dies, it stops ingesting C14, making it a timestamp.
• Plants undergo photosynthesis, herbivores eat plants, ingesting carbon.

Half-Life and Fossil Dating

• C14 has a half-life of approximately 5,730 years.
• Fossils can be dated back ~75,000 years.
• Uranium 238 (U238) in rocks surrounding fossils decays to Lead 206 (Pb206) with a half-life of 4.5 billion years.
• mya = millions of years ago.

Timeline of Species (Most Recent to Oldest)

• Placental: 110 mya
• Birds: 250 mya
• Reptiles: 320 mya
• Amphibians: 340 mya
• Bony Fish: 420 mya
• Land Vertebrates
• Worms
• Fungi, bacteria, simple amoeba

Fossils as Evidence

• Intermediate structures/species should be seen in the fossil record if heritable changes lead to new species:
• Equus family includes horses, donkeys, and zebras
• Rhinos and tapirs diverged approximately 60 mya.

Analogous vs. Homologous Structures

• Analogous structures have the same function but different origins (e.g., bird wings vs. bee wings) and lead to convergent evolution.
• Homologous structures may look different and may or may not perform the same function, but they originate from the same common ancestor and lead to divergent evolution.
• Pentadactyl limbs: All forelimbs have the same bones in the same relative order.

Artificial Selection & Vestigial Organs

• Artificial selection occurs when humans modify other species over generations by selecting for a desired trait.
• Species change faster than normal.
• Vestigial organs: Function is no longer needed, so it is selected against.
• Examples are the appendix, baby teeth in beluga whales, and pelvis/small thigh bones in snakes and whales.

Breeding & Hybrids

• Interbreeding occurs when two members of the same species mate and produce fertile offspring.
• Cross-breeding occurs when members of two different species mate, producing infertile offspring.

Genes & Environment

• The location of a gene on a chromosome is called a locus.
• The environment influences the types of species that exist in an area, often driven by food availability.
• Population variation always exists.
• A change in the environment can occur.
• Foxes with keen eyesight can spot the tails of mice.
• Either short or long tails may be advantageous for mice.
• The environment's change does not cause a change in the individual to become better adapted as adaptation must be in the gametic cell (not somatic).
• Variation is healthy for a population because it can withstand selection pressure and still survive.

Mechanisms of Adaptation

• Mutation changes the DNA sequence, producing new alleles and enlarging the gene pool.
• Gene pool = total number of alleles in a population.
• Meiosis produces new allele combinations by breaking up existing combinations in diploid cells through crossing over and independent assortment.
• Sexual reproduction is the fusion of gametes from two different parents.
• Darwin described descent with modification where descent refers to generation to generation and modification refers to adaptations.
• Variation exists because of different alleles.
• Changes in the environment create selection pressure.
• Individuals who are better adapted have a better chance of survival and passing down their genes.
• Individuals who are less well-adapted eventually die off.
• Progressive changes in the population occur over time.
• If mice were separated on two different islands and adapted to the new environment, if the two populations can still reproduce together then they are the same species.