a darwinian view of life i. darwin’s contributions ii. mendel's contributions iii. the...

A Darwinian View of LifeI. Darwin’s ContributionsII. Mendel's ContributionsIII. The Cellular Context

III. The Cellular ContextA. Cell Structure/Function Review


1. Membrane:


1. Membrane: regulates what gets in/out, largely through protein channels.


1. Membrane: regulates what gets in/out, largely through protein channels.2. Energy Harvest by protein photosystems and protein enzymes in chloroplasts AND/OR cellular respiration (protein enzymes in cytoplasm and mitochondria).

ATP


1. Membrane: regulates what gets in/out, largely through protein channels.2. Energy Harvest:

ATP


1. Membrane: regulates what gets in/out, largely through protein channels.2. Energy Harvest by protein photosystems and protein enzymes in chloroplasts AND/OR cellular respiration (protein enzymes in cytoplasm and mitochondria).3. Energy used to catalyze reactions:

ATP

RNA

PROTEIN

ribosome

Endoplasmic Reticulum


1. Membrane: regulates what gets in/out, largely through protein channels.2. Energy Harvest by protein photosystems and protein enzymes in chloroplasts AND/OR cellular respiration (protein enzymes in cytoplasm and mitochondria).3. Energy used to catalyze reactions… often building proteins by protein synthesis (reading DNA and making RNA and protein)

ATP

RNA

PROTEIN

ribosome



1. Membrane: regulates what gets in/out, largely through protein channels.2. Energy Harvest by protein photosystems and protein enzymes in chloroplasts AND/OR cellular respiration (protein enzymes in cytoplasm and mitochondria).3. Energy used to catalyze reactions… often building proteins by protein synthesis (reading DNA and making RNA and protein)4. Energy used for cell division.

ATP

RNA

PROTEIN

ribosome



1. Membrane: regulates what gets in/out, largely through protein channels.2. Energy Harvest by protein photosystems and protein enzymes in chloroplasts AND/OR cellular respiration (protein enzymes in cytoplasm and mitochondria).3. Energy used to catalyze reactions… often building proteins by protein synthesis (reading DNA and making RNA and protein)4. Energy used for cell division

ATP

RNA

PROTEIN

ribosome


DNA (genes) are recipes for proteins, and proteins are critical to cell metabolism, growth, reproduction, regulation of gene action, and response to the environment.

III. The Cellular ContextA. Cell Structure/Function ReviewB. Chromosomal Terminology 1. chromatin: indistinguishable, diffuse chromosomes

III. The Cellular ContextA. Cell Structure/Function ReviewB. Chromosomal Terminology 1. chromatin: indistinguishable, diffuse chromosomes 2. chromosome: condensed strand of chromatin, either:

unreplicated (one DNA double-helix) OR Replicated (two double-helices)

III. The Cellular ContextA. Cell Structure/Function ReviewB. Chromosomal Terminology 1. chromatin: indistinguishable, diffuse chromosomes 2. chromosome: condensed strand of chromatin, either:

unreplicated (one DNA double-helix) OR Replicated (two double-helices)

A single DNA double-helix, bound with the associated proteins (pink), is called a ‘chromatid’.

An unreplicated chromosome has one chromatid.

A replicated chromosome has two chromatids that are IDENTICAL COPIES

III. The Cellular ContextA. Cell Structure/Function ReviewB. Chromosomal Terminology 1. chromatin: indistinguishable, diffuse chromosomes 2. chromosome: condensed strand of chromatin 3. “Ploidy” refers to the “information content” in the cell… how many

‘sets’ of chromosomes are there?



- in simplistic terms, if a cell has ‘one gene for every trait’ = haploid (1n)

A

b

C

d



- in simplistic terms, if a cell has ‘one gene for every trait’ = haploid (1n) - we then make reference to the NUMBER of chromosomes present: “1n = 2”

A

b

C

d




- In eukaryotes, gametes and spores are haploid (typically)

A

b

C

d




- A haploid set is also called the ‘genome’ – representing all the genetic information needed to encode an organism of that species.

Species Haploid Number

Domestic cat 19

Human 23

Chicken 39

Dog 39

Water Fly 80



- In eukaryotes, gametes and spores are haploid (typically) - bacteria and archaeans have one circular chromosome and so are haploid organisms that do NOT reproduce by gamete production/fusion.

A

b

C

d



A

b

C

d

a

B

C

D

- when haploid gametes fuse during fertilization, a zygote with two genes for every trait is formed. This cell is DIPLOID, 2n = 4.



A

b

C

d

a

B

C

D

- when haploid gametes fuse during fertilization, a zygote with two genes for every trait is formed. This cell is DIPLOID, 2n = 4.

- NOTE that the two chromosomes of the same color are not IDENTICAL. They govern the same traits, but the genes that they have for these traits can be different alleles (forms of a gene) that influence that trait in different ways. Chromosomes that govern the same traits are called HOMOLOGOUS



- Many organisms (indeed, maybe MOST flowering plant species) are POLYPLOID, and have several sets of chromosomes… like this Tetraploid (4n = 8).

A

b

C

d

a

B

C

D

A

b

C

d

A

b

C

d



- Many organisms (indeed, maybe MOST flowering plant species) are POLYPLOID, and have several sets of chromosomes… like this Tetraploid (4n = 8).

A

b

C

d

a

B

C

D

- when it makes gametes/spores (with ½ the genetic info as the parent cell), it will make diploid gametes… so not ALL gametes are haploid.

A

b

C

d

A

b

C

d


‘sets’ of chromosomes are there? 4. Chromosomes are identified and classified by their length, banding

pattern, and position of the centromere.

http://jmg.highwire.org/content/38/2/125/F1.large.jpg

III. The Cellular ContextA. Cell Structure/Function ReviewB. Chromosomal TerminologyC. The Cell Cycle


- Interphase:

Poorly named – the cell is most active metabolically, growing, building proteins, replicating its DNA, and preparing for division.

Chromosomes are diffuse – “chromatin” – DNA recipes are being ‘read’ and proteins are synthesized, or DNA is being replicated.

Three substages: G1, S, G2


- Interphase: G1: the cell is most active metabolically, growing and building proteins appropriate for that cell. Cell may be “arrested” in this stage and not divide again (neurons, muscle). If so, it is more appropriately said that the cell has entered the G0 stage. The cell also ‘proof-reads’ and repairs DNA during this stage.



S: (“synthesis”) DNA replication occurs; each chromosome transitions from its unreplicated (one DNA double-helix) to its replicated (two DNA double-helices) state.



S: (“synthesis”) DNA replication occurs; each chromosome transitions from its unreplicated (one DNA double-helix) to its replicated (two DNA double-helices) state.

G2: Preparatory for division; in animals, centrioles are made during this period. DNA is repaired (and errors made during replication) can be corrected before division.


- Interphase: - “Checkpoints”:

The transition from G1 is critical; when a cell crosses this ‘checkpoint’ late in G1, it is committed to dividing.

Likewise, the transition from G2 is critical, because the DNA will be passed to daughter cells in its present state.

If these checks are poorly regulated, cells can divide prematurely, before DNA proof-reading is complete. This increases the number of mutations passed to daughter cells, leading to further problems with cell division regulation. Ultimately, cells may keep dividing with little or no regulation, as a tumor.

III. The Cellular ContextA. Cell Structure/Function ReviewB. Chromosomal TerminologyC. The Cell CycleD. Cell Division: Mitosis

LE 12-9a

Cleavage furrow100 µm

Contractile ring ofmicrofilaments

Daughter cells

Cleavage of an animal cell (SEM)

LE 12-9b

1 µm

Daughter cells

Cell plate formation in a plant cell (TEM)

New cell wallCell plate

Wall ofparent cell

Vesiclesformingcell plate


E. Meiosis1. Overview

2n

1n

1n

1n

1n

1n1n

REDUCTION DIVISION

E. Meiosis1. Overview2. Meiosis I (Reduction)

There are four replicated chromosomes in the initial cell. Each chromosomes pairs with its homolog (that influences the same suite of traits), and pairs align on the metaphase plate. Pairs are separated in Anaphase I, and two cells, each with only two chromosomes, are produced. REDUCTION



PROPHASE I: - leptonema: condensation begins, and “homolog search” occurs

- zygonema: condensation continues and homologs align and begin to interact

- pachynema: condensation is completed, and the homologs synapse – chemically bound along length, and exchange of DNA between homologs occurs (crossing over)

- diplonema: homologs begin to separate, and points of contact (chiasma) are thought to indicate where crossing over occurred.

- diakinesis: separation of homologs and breakdown of nuclear envelope; attachment of spindle fibers

E. Meiosis1. Overview2. Meiosis I (Reduction)3. Transition4. Meiosis II (Division)

Each cell with two chromosomes divides; sister chromatids are separated. There is no change in ploidy in this cycle; haploid cells divide to produce haploid cells.DIVISION

5. Modifications in anisogamous and oogamous species


E. MeiosisF. Sexual Reproduction and Variation

1. Meiosis and Mendelian Heredity: The chromosomal theory of inheritance

F. Sexual Reproduction and Variation

1. Meiosis and Mendelian Heredity: The chromosomal theory

Sutton and Boveri (independently) saw homologous chromosomes separating (segregating) during meiosis. If they carried genes, this would explain Mendel’s first law.

Theodor Boveri

Walter Sutton

A a

http://en.wikipedia.org/wiki/File:Theodor_Boveri.jpg



And if the way one pair of homologs separated had no effect on how others separated, then the movement of homologs would explain Mendel’s second law, also!

They proposed that chromosomes carry the heredity information.

Theodor Boveri

Walter Sutton

A aA a

b BB b

AB ab Ab aB

OR

http://en.wikipedia.org/wiki/File:Theodor_Boveri.jpg



2. Solving Darwin’s Dilemma

Independent Assortment produces an amazing amount of genetic variation.

Consider an organism, 2n = 4, with two pairs of homologs. They can make 4 different gametes (long Blue, Short Red) (Long Blue, Short Blue), (Long Red, Short Red), (Long Red, Short blue). Gametes carry thousands of genes, so homologous chromosomes will not be identical over their entire length, even though they may be homozygous at particular loci.

Well, the number of gametes can be calculated as 2n

or





Consider an organism with 2n = 6 (AaBbCc) ….There are 2n = 8 different gamete types.

ABC abcAbc abCaBC AbcAbC aBc


1. Meiosis and Mendelian Heredity: The chromosomal theory2. Solving Darwin’s Dilemma



And humans, with 2n = 46?






And humans, with 2n = 46?

223 = ~ 8 million different types of gametes.

And each can fertilize ONE of the ~ 8 million types of gametes of the mate… for a total 246 = ~70 trillion different chromosomal combinations possible in the offspring of a single pair of mating humans.


1. Meiosis and Mendelian Heredity: The chromosomal theory2. Solving Darwin’s Dilemma3. Model of Evolution – circa 1905

Sources of Variation Causes of Change

Independent Assortment VARIATION NATURAL SELECTION

a darwinian view of life i. darwin’s contributions ii. mendel's contributions iii. the...

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