The National Academy of Sciences In everyday usage: "theory" often refers to a hunch or a speculation. The word, “theory” is often used when drawing a conclusion based on inconclusive evidence. The formal scientific definition of theory: It refers to a comprehensive explanation of some aspect of nature that is supported by a vast body of evidence.

National Academy of Sciences “Scientific theories are so well-established that no new evidence is likely to alter them substantially.” Example: No New Evidence will Demonstrate:Example: No New Evidence will Demonstrate: –that the Earth does not orbit around the sun (heliocentric theory) –that living things are not made of cells (cell theory) –that matter is not composed of atoms (atomic theory) –that the surface of the Earth is not divided into solid plates that have moved over geological timescales (the theory of plate tectonics) How does this relate to the theory of evolution?How does this relate to the theory of evolution? –It is supported by so many observations and confirming experiments that the basic components of the theory will not be overturned by new evidence. –However, like all scientific theories, the theory of evolution is subject to continuing refinement as new areas of science emerge or as new technologies enable observations and experiments that were not possible previously.

Micro-Evolution Chapter 17

Individual organisms DO NOT evolve. Populations of organisms do. Micro-Evolution is one way that evolution occurs. Micro-Evolution simply refers to a change in allelic frequency within a population of organisms

PopulationPopulation – a group of individuals belonging to the same species, occupying the same given area They exhibit variation among the individual members, but they also hold certain morphological (structural), physiological (functional), and behavioral traits in common.

–Alleles –Alleles – each gene exists in 2 or more slightly different molecular forms. Offspring inherit the parent’s alleles and express them in their phenotypes. Bb b B

Section 10.1 Summary – pages Chromosome # 1 Inherited from mom Gene for Hair Texture Chromosome # 1 Inherited from dad Gene for Hair Texture Mom’s allele codes for Straight hair Dad’s allele codes for Curly hair

Section 15.2 Summary– pages Picture all of the alleles of a population as being together in a large pool called a gene pool. The percentage of any specific allele in the gene pool is called the allelic frequency. Look around the room…. What is the gene pool for hair color??? What is the allelic frequency of people with blonde hair?

5 Factors that affect the mix of alleles during gamete formation and fertilization Gene mutations create new allelesGene mutations create new alleles Crossing over and genetic recombination are normal results of meiosis (sex cell creation).Crossing over and genetic recombination are normal results of meiosis (sex cell creation). Independent assortment of chromosomes occurs in meiosis (when sex cells are created).Independent assortment of chromosomes occurs in meiosis (when sex cells are created). Fertilization between genetically varied gametes produces “new” combinations of genesFertilization between genetically varied gametes produces “new” combinations of genes Abnormal changes in chromosome structure or number can occur.Abnormal changes in chromosome structure or number can occur.

MutationsMutations – heritable changes in DNA that can alter gene expression. Mutations are random and the phenotypic outcome may be neutral, beneficial, harmful, or lethal to the individual depending on other interactions

The Effect of Mutations Lethal MutationLethal Mutation an expression of a gene that results in death Neutral MutationNeutral Mutation have no effect on survival and reproduction regardless of whether or not they are expressed in a phenotype Beneficial MutationsBeneficial Mutations provide some survival advantage

Mutation: Remix Mutations are the ONLY source of NEW alleles. This is the genetic foundation for biological diversity.

Recombination & Crossing Over Chromosomal crossover - recombination between the paired chromosomes inherited from each of one's parents, generally occurring during meiosis. Homologous sites on two chromatids can mesh with one another, and may exchange genetic information

Crossing-Over Crossing over can occur at any location on a chromosome, and it can occur at several locations at the same time. This causes the traits found in each gamete varied. This is why siblings of the same parents can look so different from each other.

FROM MOM FROM DAD This chromosome inherited by mom could code for straight hair, brown hair, and green eyes… This chromosome inherited by dad could code for curly hair, black hair, and brown eyes… After crossing-over Now one chromosome passed on to offspring could have traits from both homologous… curly hair, brown hair, and green eyes…

Section 10.1 Summary – pages genes for different traits—(for example, eye shape and eye color)— are inherited independently of each other. The Law of Independent Assortment Bb bb rrRR Bb Rr

Section 10.2 Summary – pages Fertilization Zygote

Chromosomal Abnormalities

Micro-Evolution Those factors lead to variation and change in alleles before birth. Change in allele frequencies within a population can also be brought about by non-genetic factors: genetic drift, gene flow, and natural selection.

Genetic Drift Genetic DriftGenetic Drift – the random fluctuation in allele frequencies over time, due to chance occurrences alone It is when few individuals rebuild a population It increases the chance of any given allele becoming more or less prevalent

Bottleneck EffectBottleneck Effect – When a disturbance greatly reduces the size of a population leaving a few individuals to reestablish the population Disease/Pollution Habitat loss Predation/Hunting Deforestation in the Amazon

Founder EffectFounder Effect – a few individuals leave the original population to establish a new one. They may or may not carry phenotypes that are common to other members of the original population Speciation may occur rapidly due to chance allelic frequencies of the “founder” organisms that differ from the original population.

Inbreeding: Possible bad side to genetic drift Mating among closely related individuals It tends to increase deleterious homozygous recessive conditions, thus leading to lower viability and survival rates. Reduced fertility both in litter size and sperm viabilityfertilitysperm Increased genetic disordersgenetic disorders Fluctuating facial asymmetryfacial asymmetry Higher infant mortalityinfant mortality Slower growth rategrowth rate Smaller adult sizeadult Loss of immune system functionimmune system

The problem that all endangered or threatened species encounter is this tendency to be forced to “inbreed”. When there are only 100 of a species left, and they are forced to inbreed…then the tendency is for genetic diversity to diminish even further. So what??? Why is genetic diversity important? Another consequence of inbreeding in small populations is that recessive and possibly fatal combinations of alleles becomes greater. Ethiopian Wolf Genetic diversity gives species the chance to evolve. It provides enough variation for possible positive evolutionary outcomes.. The smaller the population, the less likely that is to occur.

Gene Flow Genes move with individuals when they move (emigrate or immigrate) into and out of a population…and it changes the gene pool

Essence of Darwin’s Ideas (1)Variation exists in natural populations (2) Many more offspring are born each season than can possibly survive to maturity (3) As a result, there is a struggle for existence - competition - competition (4) Characteristics beneficialin the struggle for existence will tend to become more common in the population, changing the average characteristics of the population over time. (4) Characteristics beneficial in the struggle for existence will tend to become more common in the population, changing the average characteristics of the population over time.

Natural Selection Accounts for more changes in allele frequencies than any other micro-evolutionary process When organisms with the most beneficial traits in a population are the ones that survive and reproduce, and pass those traits on…