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Biological basis of life and Mendel - · PDF file Modern synthesis in the later 1920s-early 30s. Evolution now defined in two stages 1. Variation - inherited differences among organisms

Oct 18, 2020




  • Biological basis of life and Mendel


  • Agenda 1. Explain Quiz 1 (take home) 2. Good short answer questions and good essays 3. (Very brief description of topics so far) 4. Modern examples of evolution in action 5. Early issues with Darwin's theory of natural selection 6. Rival hypotheses - why intelligent design isn't science


  • Quiz 1 Probably have them up tonight

    NEXT quiz


  • Natural Selection in Action Reproductive 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.


  • 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


  • 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


  • Genetics Genetics studies gene structure and action

    Genetic mechanisms undergird evolutionary change


  • 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


  • Cells - General Composition Organelles - substructures in the cell performing various functions E.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


  • Cells - Two types Somatic 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)


  • Proteins Function - 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


  • DNA DNA (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


  • DNA Structure -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 Cytosine 13

  • Protein Synthesis DNA 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


  • Protein Synthesis - Two stages 1. 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


  • DNA Replication Growth 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 replication 1. Enzymes 'unzip' bonds between the bases 2. Separated nucleotide chains act as templates for the formation of a new nucleotide strand 3. Unattached nucleotides pair with complementary bases


  • 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)


    Composition: 100s-1000s of nucleotide bases Organization: coding and noncoding segments

    Function Regulatory genes - to switch on/off other DNA segments. E.g., Hox genes - direct body plan development and embryonic tissue segmentation. 17

  • Chromosomes After DNA replication, DNA becomes tightly coiled to form chromosomes

    Chromosomes Structure - single-stranded during normal cell functioning and double-stranded during cell division

    Types of chromosomes Autosomes - govern all physical characteristics minus sex determination Sex chromosomes - X and Y XX - mammal females XY - mammal males


  • Chromosomes Humans have 46 chromosomes, whereas gorillas and chimpanzees have 48.

    Karyotype - Chromosomes are visible during cell division


  • 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-stranded lls 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


  • Mitosis and Meiosis - types of cell division Recap Mitosis -Somatic cells (i.e., body cells - skin, hair, muscle, etc.) are duplicated -ONE division produces cells with all 46 chromosomes Results: 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 chromosomes Results: four daughter cells, not genetically identical


  • 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


  • Cell Division - Complications in meiosis and Sex Chromosomes Complications with meiosis

    98% of newborns have correct numbers of chromosomes 50% 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.


  • Mutations Any 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.


  • NEW genetic information? Recombination generates new combinations of genetic information


    Mutations - changes in the nucleotide sequence of DNA -Only way NEW genetic variation is introduced


  • Chapter Four Mendel and Modern Evo


  • Natural selection a

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