Darwin's theory of natural selection, its rivals, and cells. Week 3 (finish ch 2 and start ch 3)

Transcription

1 Darwin's theory of natural selection, its rivals, and cells Week 3 (finish ch 2 and start ch 3) 1

2 Racap of Darwin's theory of natural selection Natural selection -mechanism explaining evolutionary change -influenced by previous scientists and Darwin's observations. Summary of NS -there's always variation of heritable traits for all members of a species -traits are advantageous (increase reproductive success) relative to environmental context -advantageous traits accumulate over time resulting in new species. -new species can also arise due to geographic isolation. 2

3 Racap of Darwin's theory of natural selection Terms and concepts Reproductive success: number of offspring an individual can produce that live to be reproductively viable. Fitness: the relative measure of reproductive success. Selective pressures: forces in the environment influencing reproductive success. 3

4 Examples of natural selection: Galapagos finches -Local environmental conditions varied from island to island SO: NS led to different populations to diverge from each other *Differences between species = beak size and structure Heavy beaks = exploit seeds and leaves Long stout beaks = exploit insects in trees (like a woodpecker) Long thin beaks = exploit flying insects 4

5 NS ex: Antibiotic resistance in bacteria Recall: environmental pressures make certain variations do better than others. Environmental pressure: advent and extensive use of antibiotics Selection for: advantageous traits like higher resistance to antibiotics -Over many generations, a new resistant bacterial species emerges. 5

6 Conditions for NS to occur Examples highlight important conditions needed for natural selection i. NS only acts on heritable traits ii. NS only acts on already existing variation in heritable traits iii. Fitness is a relative measure that changes as the environment changes iv. NS only acts on traits that affect reproduction 6

7 Example 1: Dog breeding Q: How could you turn a pack of wolves into Chihuahuas? If you're given a pack of wolves to breed, how would you start breeding the wolves to eventually make a Chihuahua? Note: All dogs descended from wolves 7

8 Constraints on Darwin's theory of natural selection First constraint: Didn't know why biological variation occurs in all species. Second constraint: Didn't know how traits were inherited traits -Blending inheritance fails Much later, -advancements in scientific technology -advancements in cell biology and genetics -the rediscovery of Mendel's principles of inheritance...allowed us to overcome these constraints on Darwin's theory 8

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17 Chapter 3: Biological basis of life: genetics, cells, DNA 17

18 Constraints on Darwin's theory of natural selection First constraint: Didn't know why biological variation occurs in all species. Second constraint: Didn't know how traits were inherited traits 18

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23 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 23

24 DNA Structure Structure DNA is made of complementary chains of stacked nucleotides Nucleotides structure: composed of a sugar plus a phosphate (sides), and a nitrogenous base (rungs) Bases: form complementary bonds Adenine bonds with Thymine Guanine bonds with Cytosine 24

25 DNA Replication DNA can make multiple copies of itself to -key to growth and healing/repairing tissue -is needed for cell division Process of DNA replication 1. Enzymes 'unzip' bonds between the bases 2. Exposed bases attract complementary free-floating nucleotides 3. Two parental nucleotide chains are models for growing replicated strands -the new DNA molecules consist of an original and new strand 25

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29 Proteins Function: attach to molecules to perform different functions Hemoglobin (Hb) - binds w/ oxygen and transports it around 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 29