1=Adaptaion Chapter by Natural Selection
Darwins Theory of Adaptation
(The struggle for existence, variation in fitness, and the inheritance of variation)
1. The ability of a population to expand is infinite, environmental support is finite
(because sources are finite, not all individuals will be able to survive and reproduce; organisms reproduce until
environment can no longer sustain them)
2. Organisms within populations vary, and this variation allows for survival and reproduction
(some will possess traits that help them reproduce more successfully-adaptations)
3. This variation is transmitted from parent to offspring (inherited)
(If traits heritable they will be passed on to offspring and be more common in successive generations)
Natural Selection-evolution by variation and selective retention
An Example of Adaptation by Natural Selection
*Finches
Supply of food was not sufficient to sustain population; beak depth varied among finches and affected birds survival (large
beaked birds ^ small beaked birds decreased; average beak depth increased (small beaked birds died)
Morphology-an organisms size, shape and composition
Selection preserves the status quo when the most common type is best adapted
(birds with large beaks less likely to survive juvenile period-require more food)
Equilibrium-neither gene frequencies nor phenotypes change
Stabilizing selection-process that produces equilibrium
Populations characteristics susceptible to change as well =)
Species-dynamic population of individuals that may or may not change over time
Stasis/not natural state of species but prevalent when the most favored type is most common-favored by stabilizing selection
INDIVIDUAL SELECTION
Adaptation results from the competition among individuals, not between the entire populations or species
Selection produces adaptation that benefits individuals
(often selection leads to changes in behavior/morphology that increase the reproductive success of individuals but decreases that
of the group, population, species)
*organisms produce more offspring than necessary to maintain species (individual vs. group)
i.e. 10 babies, two good enough to reproduce, other 8 waste of resources to population, reproduction does not decrease for better
of group but ^ because natural selection favored for females who produce more offspring
fecundity-ability to produce offspring
high producing baby makes ^ deplete resources faster and thus species has increased likelihood of becoming extinct
THE EVOLUTION OF COMPLEX ADAPTATIONS
WHY SMALL VARIATIONS ARE IMPORTANT?
Continuous variation- i.e. height (short to tall)
Discontinuous variation- distinct types with no intermediate forms
Achondroplasia-genetic disorder that causes people to be really short (short arms and legs)
Discontinuous variants-rare in nature (unlikely that complex things will arise in a single jump)
Complex adaptations can arise through the accumulation of small random variations by natural selection
Continuous variation essential for complex adaptations-cumulative
Why Intermediate Steps Are Favored by Natural Selection?
Evolution of complex adaptations needs intermediate steps to be favored by natural selection as well
Steps like a tinkerer
*does not predict that every possible adaptation or most will even occur
Sometimes unrelated species have independently evolved the same complex adaptation, that the evolution of complex adaptations
by natural selection is not a matter of mere chance
Convergence- the evolution of similar adaptations in unrelated groups of animals
i.e. marsupial and placental fauna (placental fauna)
RATES OF EVOLUTIONARY CHANGE
more complex changes usu. Take longer to evolve but evidence for complex changes in shorter life spans in remarkable short
periods of time
*artificial selection of plants and animals---human manipulated within a few hundred years
Organisms with shorter lifespans evolve more slowly than those with longer lifespans
Darwins Difficulties Explaining Variation
*blending inheritance model- a model of inheritance that assumes that the mother and father each contribute a hereditary
substance that mixes or blends
Same intermediates with blending, no variation
Selection works to blend things out and deplete variation required for adaptations-dominant recessive and genes*
Chapter 2=Genetics
Mendelian Genetics
FO, F1, F2 Generations
1. Heritable traits from mother and father genes
2. Each gene is equally likely to be inherited when gametes are formedindependent assortment
Cell Division and The Role of Chromosomes in Inheritance
Chromosomes-small linear bodies contained in every cell and replicated during cell division; replicated in a special way that
creates gametes
Mitosis and Meiosis
Nucleus divide when cells divide=mitosis
Diploid organisms-chromosomes come in homologous pairs, vary in amount that cells have
1. Original set of chromosomes duplicated
2. Chromosomes present even when cell not divided
Meiosis-produces gametes
Gametes-only contain 1 copy of each chromosome-haploid egg and sperm unite to form diploid zygote
Chromosomes and Mendels Experimental Results
Alleles-varieties of genes that have the same effect on the same organism
Homozygous-two copies of same allele
Heterozygous- different copies of same allele
Genotype, phenotype, dominant, recessive,
Linkage and Recombination
Recombination-variety of genes caused by genetic shuffling-extremely important for maintaining variation
Locus-site where specific genes are on a particular chromosome
Genome-all of the genes carried on all of the chromosomes are referred to as the genome
*traits may not segregate independently if they are affected by genes on the same chromosome
Loci for different traits appear on same chromosome-linked
Loci on different chromosomes-unlinked
Molecular Genetics
Chromosomes contain protein and DNA
Genes are DNA
DNA in protein coding genes-specify the structure of proteins; many proteins are enzymes which regulate much of the
biochemical machinery of organisms
Regulatory genes-determines the conditions under which the message encoded in protein coding gene will be expressedshaping differentiation of cells during development
Proteins=are made of amino acids
Primary Structure-determined by sequence
Tertiary structure-essential for catalytic function
Codons code for amino acids (three-letter combinations)
Facsimile of one of the strands of DNA-RNA-Before DNA is translated into proteins its message is first transcribed into
messenger RNA; amino acid s bound to a different kind of RNA called transfer RNA-triplet of bases called anticodon (each
type of tRNA bound to amino acid whose codon bonds to another anticodon (tRNA anticodon binds to mRNA codon until
all of mRNA molecule passes through the ribosome)
Prokaryotes do not have a chromosome or cell nucleus, eukaryotes do!!!!! DNA sequence that codes for protein is
uninterruptedl coding sequence in eukaryotes interrupted by noncoding regions called introns vs. exons
Alternative splicing allows the same DNA sequence to code for more than one protein
(entire DNA sequence transcribed into RNA and the introns are removed, exons are included in same order but not all)allowing for different proteins to be produced
Regulatory Sequences Control Gene Expression
DNA sequence in regulatory genes determines when protein coding genes are expressed
Repressor-protein that decreases transcription of a regulated gene
Activator-protein that increases transcription of a regulated gene
Sequences of regulatory genes control whether or not repressor and activator proteins that control transcription bind to
DNA-thus creates phenotype and variation
Combinatorial control-the control of gene expression in which more than one regulatory protein is used and expression Is
allowed only in a specific combination of conditions
NOT ALL DNA CARRIES A MESSAGE
Some RNA molecules bind together with proteins to performs a variety of cellular functions
Splicesomes(ribosomes)-organelles that splice the mRNA after introns have been snipped out
Noncoding RNA-RNA that does not code for anything-one form of short segments called microRNA (miRNA)-plays an
important role in regulating the translation of mRNA into a protein; DNA sequences occur between coding sequences and
introns; sequence is transcribed and moves out of nucleus binds to complementary RNA and prevents them from being
translated into a protein-provides an alternate form of regulation
Chromosomes contain long sequences that do not code for anything just long simple repeats