Darwin's theory of natural selection, its rivals, and cells

Week 3(finish ch 2 and start ch 3)

1

Racap of Darwin's theory of natural selectionNatural 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

Racap of Darwin's theory of natural selectionTerms 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

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 structureHeavy beaks = exploit seeds and leaves

Long stout beaks = exploit insects in trees (like a woodpecker)Long thin beaks = exploit flying insects

4

NS ex: Antibiotic resistance in bacteriaRecall: 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

Conditions for NS to occurExamples 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

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

Example 1: Dog breeding

Constraints on Darwin's theory of natural selectionFirst 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

9

10

11

12

13

14

15

16

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

17

Constraints on Darwin's theory of natural selectionFirst constraint: Didn't know why biological variation occurs in all species.

Second constraint: Didn't know how traits were inherited traits

18

19

20

21

22

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

23

DNA StructureStructureDNA is made of complementary chains of stacked nucleotides

Nucleotides structure: composed of a sugar plusa phosphate (sides), and a nitrogenous base (rungs)

Bases: form complementary bonds

Adenine bonds with Thymine

Guanine bonds with Cytosine

24

DNA ReplicationDNA can make multiple copies of itself to-key to growth and healing/repairing tissue-is needed for cell division

Process of DNA replication1. Enzymes 'unzip' bonds between the bases2. Exposed bases attract complementary free-floating nucleotides3. Two parental nucleotide chains are models for growing replicated strands

-the new DNA molecules consist of an original and new strand

25

26

27

28

ProteinsFunction: 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