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

Oct 18, 2020

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

Biological basis of life and Mendel

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Page 2: Biological basis of life and Mendel - WordPress.com · Modern synthesis in the later 1920s-early 30s. Evolution now defined in two stages 1. Variation - inherited differences among

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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Page 3: Biological basis of life and Mendel - WordPress.com · Modern synthesis in the later 1920s-early 30s. Evolution now defined in two stages 1. Variation - inherited differences among

Quiz 1Probably have them up tonight

NEXT quiz

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Page 4: Biological basis of life and Mendel - WordPress.com · Modern synthesis in the later 1920s-early 30s. Evolution now defined in two stages 1. Variation - inherited differences among

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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Page 5: Biological basis of life and Mendel - WordPress.com · Modern synthesis in the later 1920s-early 30s. Evolution now defined in two stages 1. Variation - inherited differences among

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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Page 6: Biological basis of life and Mendel - WordPress.com · Modern synthesis in the later 1920s-early 30s. Evolution now defined in two stages 1. Variation - inherited differences among

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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Page 7: Biological basis of life and Mendel - WordPress.com · Modern synthesis in the later 1920s-early 30s. Evolution now defined in two stages 1. Variation - inherited differences among

GeneticsGenetics studies gene structure and action

Genetic mechanisms undergird evolutionary change

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Page 8: Biological basis of life and Mendel - WordPress.com · Modern synthesis in the later 1920s-early 30s. Evolution now defined in two stages 1. Variation - inherited differences among

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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Page 9: Biological basis of life and Mendel - WordPress.com · Modern synthesis in the later 1920s-early 30s. Evolution now defined in two stages 1. Variation - inherited differences among

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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Page 10: Biological basis of life and Mendel - WordPress.com · Modern synthesis in the later 1920s-early 30s. Evolution now defined in two stages 1. Variation - inherited differences among

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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Page 11: Biological basis of life and Mendel - WordPress.com · Modern synthesis in the later 1920s-early 30s. Evolution now defined in two stages 1. Variation - inherited differences among

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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Page 12: Biological basis of life and Mendel - WordPress.com · Modern synthesis in the later 1920s-early 30s. Evolution now defined in two stages 1. Variation - inherited differences among

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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Page 13: Biological basis of life and Mendel - WordPress.com · Modern synthesis in the later 1920s-early 30s. Evolution now defined in two stages 1. Variation - inherited differences among

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

Page 14: Biological basis of life and Mendel - WordPress.com · Modern synthesis in the later 1920s-early 30s. Evolution now defined in two stages 1. Variation - inherited differences among

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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Page 15: Biological basis of life and Mendel - WordPress.com · Modern synthesis in the later 1920s-early 30s. Evolution now defined in two stages 1. Variation - inherited differences among

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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Page 16: Biological basis of life and Mendel - WordPress.com · Modern synthesis in the later 1920s-early 30s. Evolution now defined in two stages 1. Variation - inherited differences among

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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Page 17: Biological basis of life and Mendel - WordPress.com · Modern synthesis in the later 1920s-early 30s. Evolution now defined in two stages 1. Variation - inherited differences among

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

Page 18: Biological basis of life and Mendel - WordPress.com · Modern synthesis in the later 1920s-early 30s. Evolution now defined in two stages 1. Variation - inherited differences among

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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Page 19: Biological basis of life and Mendel - WordPress.com · Modern synthesis in the later 1920s-early 30s. Evolution now defined in two stages 1. Variation - inherited differences among

ChromosomesHumans have 46 chromosomes, whereas gorillas and chimpanzees have 48.

Karyotype - Chromosomes are visible during cell division

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Page 20: Biological basis of life and Mendel - WordPress.com · Modern synthesis in the later 1920s-early 30s. Evolution now defined in two stages 1. Variation - inherited differences among

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

Page 21: Biological basis of life and Mendel - WordPress.com · Modern synthesis in the later 1920s-early 30s. Evolution now defined in two stages 1. Variation - inherited differences among

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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Page 22: Biological basis of life and Mendel - WordPress.com · Modern synthesis in the later 1920s-early 30s. Evolution now defined in two stages 1. Variation - inherited differences among

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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Page 23: Biological basis of life and Mendel - WordPress.com · Modern synthesis in the later 1920s-early 30s. Evolution now defined in two stages 1. Variation - inherited differences among

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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Page 24: Biological basis of life and Mendel - WordPress.com · Modern synthesis in the later 1920s-early 30s. Evolution now defined in two stages 1. Variation - inherited differences among

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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Page 25: Biological basis of life and Mendel - WordPress.com · Modern synthesis in the later 1920s-early 30s. Evolution now defined in two stages 1. Variation - inherited differences among

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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Page 26: Biological basis of life and Mendel - WordPress.com · Modern synthesis in the later 1920s-early 30s. Evolution now defined in two stages 1. Variation - inherited differences among

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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Page 27: Biological basis of life and Mendel - WordPress.com · Modern synthesis in the later 1920s-early 30s. Evolution now defined in two stages 1. Variation - inherited differences among

Chapter Four Mendel and Modern Evo

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Page 28: Biological basis of life and Mendel - WordPress.com · Modern synthesis in the later 1920s-early 30s. Evolution now defined in two stages 1. Variation - inherited differences among

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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Page 29: Biological basis of life and Mendel - WordPress.com · Modern synthesis in the later 1920s-early 30s. Evolution now defined in two stages 1. Variation - inherited differences among

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

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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Page 31: Biological basis of life and Mendel - WordPress.com · Modern synthesis in the later 1920s-early 30s. Evolution now defined in two stages 1. Variation - inherited differences among

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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Page 32: Biological basis of life and Mendel - WordPress.com · Modern synthesis in the later 1920s-early 30s. Evolution now defined in two stages 1. Variation - inherited differences among

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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Page 33: Biological basis of life and Mendel - WordPress.com · Modern synthesis in the later 1920s-early 30s. Evolution now defined in two stages 1. Variation - inherited differences among

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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Page 34: Biological basis of life and Mendel - WordPress.com · Modern synthesis in the later 1920s-early 30s. Evolution now defined in two stages 1. Variation - inherited differences among

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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Page 35: Biological basis of life and Mendel - WordPress.com · Modern synthesis in the later 1920s-early 30s. Evolution now defined in two stages 1. Variation - inherited differences among

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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Page 36: Biological basis of life and Mendel - WordPress.com · Modern synthesis in the later 1920s-early 30s. Evolution now defined in two stages 1. Variation - inherited differences among

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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Page 37: Biological basis of life and Mendel - WordPress.com · Modern synthesis in the later 1920s-early 30s. Evolution now defined in two stages 1. Variation - inherited differences among

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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Page 38: Biological basis of life and Mendel - WordPress.com · Modern synthesis in the later 1920s-early 30s. Evolution now defined in two stages 1. Variation - inherited differences among

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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Page 39: Biological basis of life and Mendel - WordPress.com · Modern synthesis in the later 1920s-early 30s. Evolution now defined in two stages 1. Variation - inherited differences among

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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Page 40: Biological basis of life and Mendel - WordPress.com · Modern synthesis in the later 1920s-early 30s. Evolution now defined in two stages 1. Variation - inherited differences among

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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Page 41: Biological basis of life and Mendel - WordPress.com · Modern synthesis in the later 1920s-early 30s. Evolution now defined in two stages 1. Variation - inherited differences among

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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Page 42: Biological basis of life and Mendel - WordPress.com · Modern synthesis in the later 1920s-early 30s. Evolution now defined in two stages 1. Variation - inherited differences among

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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Page 43: Biological basis of life and Mendel - WordPress.com · Modern synthesis in the later 1920s-early 30s. Evolution now defined in two stages 1. Variation - inherited differences among

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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Page 44: Biological basis of life and Mendel - WordPress.com · Modern synthesis in the later 1920s-early 30s. Evolution now defined in two stages 1. Variation - inherited differences among

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

Page 45: Biological basis of life and Mendel - WordPress.com · Modern synthesis in the later 1920s-early 30s. Evolution now defined in two stages 1. Variation - inherited differences among

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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