Biological basis of life and Mendel 1
Biological basis of life and Mendel
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Agenda1. Explain Quiz 1 (take home)2. Good short answer questions and good essays3. (Very brief description of topics so far)4. Modern examples of evolution in action5. Early issues with Darwin's theory of natural selection6. Rival hypotheses - why intelligent design isn't science
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Quiz 1Probably have them up tonight
NEXT quiz
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Natural Selection in ActionReproductive success: Favorable traits are inherited at a higher frequency while unfavorable traits decrease over time.
Selective pressures: Environmental influences on reproductive success.
Fitness: Relative measure of reproductive success.
Adaptations: The evolutionary shifts in the variation of traits in a population in response to environmental changes.
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Natural Selection - Insights Gained from examples
1. Traits are inherited: otherwise natural selection cannot act
2. Populations have biological variation of characteristics-Selection only works on pre-existing variation
3. Fitness is relative: it changes relative to environmental change-Finch beak size correlates with long periods of drought
4. Natural selection only acts on traits affecting reproduction
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Natural Selection - Main Points*Darwin recognized that it was variation among the individuals of a population that contributed to the change in a species over time.
Natural selection operates on individuals but the population evolves
Unit of Natural Selection - Individual
Unit of Evolution - Population
Populations genetically change over time
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GeneticsGenetics studies gene structure and action
Genetic mechanisms undergird evolutionary change
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Cells - fundamental units of life in all biological organisms
Eukaryotic cells - composed of proteins, lipids, nucleic acids, and carbohydrates
Proteins - molecules (structures with ≤ 2 atoms) serving different functions due to their binding to other molecules.
Protein synthesis - DNA-directed manufacturing chains of amino acids to function into protein molecules
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Cells - General CompositionOrganelles - substructures in the cell performing various functionsE.g., protein synthesis, energy storage, waste disposal, etc.
Nucleus - contains DNA and RNA
Ribosomes - organelles in part made up of RNA; involved in protein synthesis
Mitochondria - powerhouse of the cell - produces energy; think: cell's engines; also has DNA: mtDNA
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Cells - Two typesSomatic cells - body tissues e.g., organs, brain, bone, and muscle
Sex cells (gametes) - unites with another gamete from each parent which forms a zygote. They transmit genetic information from parents to offspring.
Zygote - Potential to develop into a new organism, contains all the chromosomes (46 for us)
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ProteinsFunction - attach to various molecules to perform different functions
Hemoglobin (Hb) - binds w/ oxygen and transports it around the body
Collagen - (tissue composition) - most common protein in the body
Enzymes - regulate chemical reactions; E.g., digestive enzyme lactase breaks down lactose into simpler sugars.
Hormones - affect different tissues and organs. E.g., Insulin made by specialized pancreas cells causes the absorption of glucose in liver cells
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DNADNA (deoxyribonucleic acid) - Double-stranded host of the genetic code
RNA (ribonucleic acid) - single-stranded molecule messenger (mRNA)transfer (tRNA)
DNA + RNA contain the genetic information controlling the cell's functions
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DNAStructure-nucleotides stacked on top of each other form the double-stranded twisted ladder-like structure
Nucleotides: composed of a sugar, a phosphate (sides), and a nitrogenous base (rungs)
Bases - form complementary bonds
Adenine bonds with Thymine
Guanine bonds with Cytosine13
Protein SynthesisDNA determines the structure and function of proteins
Proteins: made of chains of amino acids
Function is determined by the number and arrangement of amino acids making up the chain
Amino acids - building blocks of proteins
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Protein Synthesis - Two stages1. Transcription (in the nucleus)-complementary strand of mRNA produced from DNA strand-m(essenger)RNA has Uracil instead of Thymine
2. Translation (in the ribosomes)-ribosomes 'read' mRNA three bases at a time (codons)-t(ransfer)RNA binds with matching codons creating amino acid chain
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DNA ReplicationGrowth and healing/repairing tissue is possible because cells are able to multiply and make exact copies of themselves.
The new copies (daughter cells) have their own DNA, which is also replicated
Process of DNA replication1. Enzymes 'unzip' bonds between the bases2. Separated nucleotide chains act as templates for the formation of a new nucleotide strand3. Unattached nucleotides pair with complementary bases
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Genes - structures and functions"a sequence of DNA bases that specifies the order of amino acids in an entire protein, a portion of a protein, or any functional product [like RNA]" (58p)
Structure
Composition: 100s-1000s of nucleotide basesOrganization: coding and noncoding segments
FunctionRegulatory genes - to switch on/off other DNA segments.E.g., Hox genes - direct body plan development and embryonic tissue segmentation. 17
ChromosomesAfter DNA replication, DNA becomes tightly coiled to form chromosomes
ChromosomesStructure - single-stranded during normal cell functioning and double-stranded during cell division
Types of chromosomesAutosomes - govern all physical characteristics minus sex determinationSex chromosomes - X and YXX - mammal femalesXY - mammal males
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ChromosomesHumans have 46 chromosomes, whereas gorillas and chimpanzees have 48.
Karyotype - Chromosomes are visible during cell division
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Mitosis - cell division for somatic cells-occurs during growth and repair of tissue
Phase 1: DNA replication - 46 single-stranded chromosomes become 46 double-stranded chromosomes.
Phase 2: Cell division - 46 double-stranded chromosomes split to comprise the genetic material in two daughter cells.
-Daughter cells are identical - 46 single-strandedhttps://www.microscopyu.com/gallery-images/mitosis-in-pig-kidney-epithelial-cells 20
Meiosis - specialized cells found in the ovaries and testes
-two cell divisions give four daughter cells -23 single-stranded chromosomes
Recombination-partner chromosomes exchange genetic info-results in non-identical daughter cells -variation is introduced into reproducing populations of organisms
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Mitosis and Meiosis - types of cell division RecapMitosis-Somatic cells (i.e., body cells - skin, hair, muscle, etc.) are duplicated-ONE division produces cells with all 46 chromosomesResults: two daughter cells, genetically identical to parents and siblings
Meiosis-Gametes (sex cells like sperm and ova in humans)-TWO divisions produces cells with only 23 chromosomesResults: four daughter cells, not genetically identical
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Unlike mitosis, meiosis involves...-Gametes transmit genetic info from parent to offspring
Crossing over: chromosomes break and reconnect onto different chromosomes which results in...
Recombination: new combinations of genetic information is created-Every generation has new genetic combinations = additional variation
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Cell Division - Complications in meiosis and Sex Chromosomes
Complications with meiosis
98% of newborns have correct numbers of chromosomes50% of pregnancies end in miscarriages. 70% of those miscarriages result from abnormal chromosome numbers.
-nondisjunction - homologous chromosomes [strands] fail to separate during meiosis - results: monosomy or trisomy Ex. Down syndrome (trisomy 21) occurs when chromosome 21 is copied three times in an individual, a phenomenon occurring 1/1000 births.
Sex chromosomes-nondisjunctions yield karyotypes XXY, XO, XXX, and XYY. Results in mental dysfunction, sterility, or lethal because - impossible to survive without an X chromosome.
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MutationsAny change in DNA e.g., point mutations - (DNA bases-changes), changes in chromosome number or structure,...
Potential effects-stop the creation of a protein-result in the creation of a defective protein, ultimately corrupting the function of a cell.
-important evolutionary consequences if they are inherited from the parent generation.
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NEW genetic information?Recombination generates new combinations of genetic information
But…
Mutations - changes in the nucleotide sequence of DNA-Only way NEW genetic variation is introduced
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Chapter Four Mendel and Modern Evo
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Natural selection and geneticsNatural selection - Traits making reproductive success more likely given environmental pressures will appear in higher frequencies from generation to generation.
Sources of Variation
*Mutations - new genetic information*Meiosis (recombination) - new combinations of genetic information
Result: new variation in every generation of sexually reproducing populations
Now we know how the variation NS needs to act on is created. (Thanks science!)
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Mendel - 1860s Monk experimenting with peasRecall: Cross-breeding - artificial selection, farmers...metaphor for natural selection
Missing in Darwin's theory of NS: a mechanism governing how traits were inherited
Background
-Mendel cross-bred pea plants-Observed the traits individual plants possessed over thousands of generations
Inferred the Principles of Inheritance
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Mendel - Cross-breeding pea plantsMendel inferred: regularity governed by a mechanism of inheritance; specifically,
*Inheritance is determined by a 'unit' (gene) offspring receive from their parents
*Individuals inherit one 'unit' from each parent for each trait
*Traits might not be expressed in an individual but can still be passed on to the next generation
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Mendel - overview-Cross-bred pea plants for thousands of generations-different trait expressions controlled by discrete units (genes)
alleles - the different expressions of a gene
The principles of inheritance
1. Segregation - for a trait, the pair of expressions from each parent separate and only one passes from parent to offspring.Meiosis - NOW we know this principle is Meiosis
2. Independent Assortment - different pairs of alleles are inherited by offspring independent from one another.
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Mendel - inferences from observationsNote: Parent plants = pureblood = homozygous for seed color
I.e., each parent had identical expressions of the 'unit' (now gene) for this trait
E.g., trait: seed color; expression: yellow or green. Y = yellow allele and G = green allele.
Parent 1 = YY
Parent 2 = GG
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Mendel's InferencesGenotype - genetic makeup of an individual (e.g., YY, GG, YG, etc)Phenotype - physical expression of an individual's genotype (e.g., yellow, green, tall, short, smooth, wrinkled, etc.)
Mendel observed: Some allele expressions dominated others.
E.g., Pea seed genotype = YG resulted in phenotype yellow so the dominant expression/form/allele = yellow (green is recessive)
E.g., Trait: height; alleles: tall T, short t
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Dominance and recessivenessRecessive - traits that are not expressed in heterozygotes
Dominance - traits that are expressed in heterozygotes AND homozygotes-these traits prevent the expression of recessive alleles in heterozygotes.
Alleles - the different expressions of a gene-genes = segments of DNA -> direct protein synthesis->found at different locus or loci of a chromosomeSince they are paired the dominant allele will be expressed
E.g., H = tall = dominant allele and h = short = recessive allele
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Mendelian traitsMendelian traits - discrete traits determined by alleles at a single genetic locus
Dominant traits = cleft chin, dwarfism;
Recessive = Phenylketonuria (PKU), albinism, sickle-cell anemiaRecessive disorders manifest if homozygous - if heterozygous, a person = unaffected but carrier
More clear with discrete Mendelian traits but gets hairy when we look at the next trait type
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Polygenic TraitsPolygenic - traits influenced by genes at 2 or more loci
E.g., stature, skin, eye, and hair color
Continuous traits - gradiation of difference in several expressions
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Mendelian Traits vs Polygenic TraitsMendelian = discrete categories of variationPolygenic = continuous
Both -determined by Mendelian principles at specific loci-Dominance and recessiveness still a factor
NOTE: Mendelian traits = less likely affected by environmental factorsEx: ABO determined at fertilization and stays constant irrespective of environmental factors.
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Modern Evolutionary TheoryModern synthesis in the later 1920s-early 30s.
Evolution now defined in two stages
1. Variation - inherited differences among organisms is produced and redistributed through various processes
2. Natural selection acts on variation resulting in differential reproductive success (85p).
-Both mutations and natural selection contribute to evolution
Current definition of Evolution:
Change in allele frequency from one generation to the next.
Allele frequencies = indicators of a group/population's genetic composition -Described as proportions or percentages of a total
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Factors that produce and redistribute variation1. Mutation - any change in DNA - bases, chromosome number &/or structure
-Random
Ex. HbS is a different allele of hemoglobin-Only affect evolution if they occur in sex cells - mutations lead to change only if they're inherited
Mutations are "the only way to produce new genes (that is, variation)" (86p).
Evolution solely due to mutation = rareOnly when combined with natural selection do we get significant/rapid evolutionary change
Ex. Point mutations - substitution of one base for another-disrupt protein production or cause production of defective proteins
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Factors that produce and redistribute variation1. Mutation
2. Gene Flow
3. Genetic Drift and Founder Effect
4. Recombination
Microevolution - small genetic changes that occur w/in a species
Macroevolution - large-scale changes that occur in populations over many generations-result in speciation
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Factors that produce and redistribute variation1. Mutation - any change in DNA - bases, chromosome number &/or structure-Random-Source of NEW variation
When combined with natural selection the rate of evolutionary change is more rapid
2. Gene Flow - the exchange of genes between populations-migration-consistent feature of human evolution
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Factors that produce and redistribute variation3. Genetic Drift - occurs solely due to small population size-randomness becomes more significant-rare alleles may disappear from a gene pool
Founder effect - small population of founders leaves a parent group to form a colony elsewhere
4. Recombination - changes the composition of chromosome parts affecting gene action
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Current theory of natural selectionNatural selection provides directional change in allele frequencies relative to specific environmental factors
If the environment changes, then selective pressures change too
If there's long-term directional change, then allele frequencies will shift gradually each generation
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Anthropology connectionsThe Human Genome Project was made possible. -sequenced all 30,000 genes humans have in their genome.
The Neandertal Genome has also been sequenced and same with the Chimpanzee genome...600 other species as well. -compare and contrast the characteristics found among the genomes in order to better understand our own evolutionary history.
Stem cells - Undifferentiated cells > able to divide and differentiate into other cell types (e.g., a cell that could become a blood, liver, or kidney cell)
Need more background but here’s a non-terrible video.https://youtu.be/evH0I7Coc54 44
Key terms and definitionsAmino acids - molecules that are the basic building blocks of proteinsChromosome - structures made up of compacted DNA and protein visible during cell replicationCodon - (also referred to as a triplet) a set of three bases coding for a specific amino acidNucleotide - the basic unit of DNA composed of a sugar, phosphate, and baseGenome - complete genetic makeup of an individual or species
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