Don’t forget! - cals.arizona.edu · The homework questions will not be collected or graded, but...

Don’t forget!The Animal Science department welcomes you back

on Wednesday at the Campbell Avenue Farm!4:30 PM; come for burgers, games and the chance to

dunk faculty members of your choiceFind out about ANS clubs and Ag student

organizationsIf you need more information, a ride or directions,

contact Maryann Harrismaharris@ag.arizona.edu

The website is up!The website is:

http://ag.arizona.edu/classes/ans213/

PLEASE NOTE: I WILL BE UPDATING THE LECTURES AND HOMEWORK PROBLEMS AS I GO.

CHECK THE WEBSITE FREQUENTLY FOR UP-TO-DATE INFORMATION

The Website…pre-emptive questionsI have replaced Lectures 1 and 2 with copies that

delete the color background. This will continue.

Color printing may still be helpful as I highlight words and concepts along the way

Lectures will be posted in both Acrobat and Powerpoint formats so you can choose your style.

Pre-emptive questions, cont.The homework questions will not be collected or

graded, but I might use some on the exam.

The homework questions will not be collected or graded, but they might show up on a test or the final.

Pre-emptive questions, cont.If you can answer the assigned problems and

understand the concepts, you will probably do very well on the test.

It’s a very good idea to go over the assigned problems.

In fact, do ALL the problems. It won’t hurt you.

“It is a profound and necessary truth that the deep things in science are not found because they are useful; they are found because it is possible to find them.”

J. Robert Oppenheimer, director of the Manhattan Project that drove development of nuclear weapons in the US during WW II.

Genetics in the News

For full text, seewww.pnas.org/cgi/doi/10.1073/pnas.0403639101

Turning Slackers Into Workaholics

Reuters 03:15 PM Aug. 11, 2004 PT

Procrastinating monkeys were turned into workaholics using a gene treatment to block a key brain compound, U.S. researchers reported on Wednesday. Blocking cells from receiving dopamine made the monkeys work harder at a task -- and they were better at it, too, the U.S. government researchers found.

Dr. Barry Richmond and colleagues at the National Institute of Mental Health used a new genetic technique to block the D2 gene. "The gene makes a receptor for a key brain messenger chemical, dopamine," Richmond said in a statement. Dopamine is a message-carrying chemical associated with rewards, movement and a variety of other important functions.

"The gene knockdown triggered a remarkable transformation in thesimian work ethic. Like many of us, monkeys normally slack off initially in working toward a distant goal," he added. For their study, Richmond and colleagues used seven rhesus monkeys. They had to push a lever in response to visual cues on a projection screen, and got a drop of water as a reward.

"They work more efficiently -- make fewer errors -- as they get closer to being rewarded. But without the dopamine receptor, they consistently stayed on-task and made few errors, because they could no longer learn to use visual cues to predict how their work was going to get them a reward."

Humans and monkeys both use this learning, which involves looking at how much work there is, visually, and deciding how long it will take to complete it. Monkeys and humans both tend to wait until the lastpossible minute to finish up the work, and become very adept at estimating how long they have.

Molecular geneticist Edward Ginns created a DNA antisense agent that tricked brain cells into turning off their D2 receptors -- which are molecular doorways used by dopamine to get into cells.Antisense involves making a kind of mirror-image molecule that looks like a strand of DNA and works to block a gene's action.

Definitions

Assumption:Assumption:The act of taking for granted, or supposing a thing

without proof; supposition; unwarrantable claim. ...

AssumptionGood science demands that you try and account for

your assumptions as best you can, but there’s no way of accounting for all of them, and they may not be true.

For example, in this experiment, the authors assumed:

The monkeys were/are representative of humans

AssumptionIs it good to increase focus or work ethic?

Why or why not? (This question is designed to make you aware of your assumptions!)

Creativity? Different learning styles?

Definitions

Hypothesis:Hypothesis:A supposition; a proposition or principle which is

supposed or taken for granted, in order to draw a conclusion or inference for proof of the point in question; something not proved, but assumed for the purpose of argument, or to account for a fact or an occurrence;

HypothesisGood science demands that a hypothesis directs the

experiment.In this case, based on the anatomical observation of

dopamine fibers in the rhinal cortex and previous studies demonstrating the importance of this region to visually-related learning, the experimenters devised the following hypothesis:

Hypothesis

If dopamine, acting through the D2 receptor, is critical for visual

association, then eliminating dopamine will alter learning behavior in monkeys

trained to do specific tasks.

Experiments TEST hypothesesAn experiment should be designed to test the

truthfulness of the hypothesis statement. This means that the data from the experiment will

either support or not support the statement.

The results?Dopamine did in fact alter learning behavior in these

monkeys, therefore, the hypothesis was correct!

Now, would you like some D2-blocker before the next test?

Moving OnReview MitosisIntroduce MeiosisIntroduce DNA ReplicationIntroduce DNA Recombination

The PlanNucleusCell DNA

Gene Expression

Individual

Group or population

Comparing Mitosis and MeiosisOne major goal of the study of genetics is to explain

the apparently conflicting forces of biology:

Heredity and VariationHeredity and VariationHow do mitosis and meiosis influence these?

Mitosis—ReviewThe cell cycle is composed of the Interphase Interphase (G1, S,

G2) and MitosisDNA is replicatedreplicated (copied) during S phaseMitosisMitosis is the process of nuclear division that results

in two genetically identical daughter cells from one progenitor cell

The process of cell division following mitosis is called cytokinesiscytokinesis

Mitosis—ReviewThe phases of mitosis are:ProphaseMetaphaseAnaphaseTelophase

Mitosis—Review

Mitosis is an important cellular process that drives both growth and development.

Both the progenitor and the daughter cells are diploid diploid (2n)

Mitosis preserves the genetic composition of cells.

Meiosis

MeiosisCell division that produces male and female gametes.

Meiosis is characterized by two division processes that results in the formation of four gametes.

Gametes are haploid haploid (n).

MeiosisMeiosis ensures genetic continuity from one

generation from the next, but at the same time, ensures genetic variation among members of the same species.

How?

MeiosisMeiosis results in the formation of haploid gametes.

The haploid gametes represent half of the genetic material present in the parent (continuity).

Crossing over or recombination of homologous regions of the chromosome shuffles the genetic material such that different gametes represent different inputs from the parent (variation).

MeiosisTwo Phases: Meiosis I – called the “reduction” division because

the number of centromeres, each representing one chromosome, is reduced by half during phase I.

Meiosis II – called the “mitotic” or “equational” division because the number of centromeres remains the same.

Meiosis: Prophase IThe most lengthy and complex step

Divided into five subdivisions

Remember, each occurs as a process with no clear borders between subdivisions.

Prophase I--LeptoteneChromosomes visible as long, thin threads

Chromosomes begin to condense

Homology search is thought to occur; this is where homologs begin to meet up prior to actual pairing.

Prophase I—ZygoteneHomologues actively pair up (absolutely critical).

Chromosomes progressively pair, side by side like a zipper.

Homologous pairing is unique to meiosis…it does not occur during mitosis

Prophase I—ZygoteneHow do the homologues pair up??

TelomeresTelomeres, the ends of the chromosomes, are thought to be important.

Telomeres are attached to the nuclear membrane, and it is likely that telomeres from homologous pairs are close to each other to facilitate pairing.

Prophase I—PachyteneChromosomes shorten and thicken further.

Chromosomes pair more intimately, called synapsissynapsis

Replicates are called sister chromatids (like mitosis), while chromatids from maternal vs. paternal members of a pair are called non-sister chromatids

Prophase I—Pachytene

Thus, each structure is composed of FOUR chromatids and is called a tetrad.

Crossing over Crossing over or recombinationrecombination, the exchange of genetic material between chromatids, occurs during the pachytene stage. This exchange produces genetic variability. The result is chromosomes that are a mosaic of both maternal and paternal contributions.

Prophase I—DiploteneIt becomes apparent that each tetrad is composed of

two pairs of sister chromatids, as each pair begins to separate.

ChiasmasChiasmas form in one or more areas where the chromatids remain in contact and represent areas where genetic exchange has taken place.

Prophase I—DiakinesisChromosomes pull farther apart

Non-sister chromatids remain loosely attached at chiasmata

Chiasmata move towards the ends of the tetrads

Prophase I—DiakinesisThe nuclear envelope and nucleolus break down

The two centromeres of each tetrad attach to newly formed spindle fibers

By the end, centromeres of each tetrad are lined up in the center of the cell

Metaphase ITerminal chiasmata appear to be the only factors

holding non-sister chromatids together

Centromeres are attached to spindle fibers and line up on the metaphase plate

Anaphase IMovement of one-half of each tetrad toward each

pole

The alignment (paternal vs. maternal) of tetrads is random, meaning that the resulting division will contain chromosomes from both sources.

Anaphase IThis random direction of chromatids toward either

pole contributes another source of variation from meiosis and is also called independent independent assortmentassortment.

Remember this later in the semester when we discuss Mendelian genetics.

Anaphase IDuring anaphase, a single centromere holds each pair

of sister chromatids together. It does not divide.

One half of each pair (called a dyaddyad) is pulled toward the pole of the cell in a process called disjunctiondisjunction.

(Non-disjunction causes asymmetric arrangement of chromosomes [Down Syndrome/Trisomy 21])

Telophase IIn most animals, a new nuclear membrane forms

around the dyads.

There is often a short interphase, but often the cell enters directly into phase two, or Meiosis II

Meiosis IIProceeds essentially like Mitosis

During prophase II, each dyad is composed of one pair of sister chromatids joined by a single centromere.

During metaphase II, the centromeres are lined up on the metaphase plate

Meiosis IIDuring anaphase II, sister chromatids from each

dyad are pulled in opposite directions and form monadsmonads.

During telophase II, one member of each pair is present at each pole.

Cytokinesis follows.

Meiosis II At the conclusion of meiosis II, each monad is a

unique combination of maternal and paternal genetic input.

The sources of variation are:1. Recombination2. Independent Assortment

Spermatogenesis vs. OogenesisThe genetic events (meiosis, crossing over,

assortment, etc.) are common between the sexes.

Cellular events differ considerably.

SpermatogenesisTakes place in the testes

Spermatogonium: undifferentiated, diploid germ cell

Primary spermatocyte: undergoes first meiotic division

Secondary spermatocyte: undergoes second meiotic division to produce haploid spermatids

SpermatogenesisSpermatids mature to become spermatozoa, four

identical spermatozoa per original primaryspermatocyte.

Spermatozoa consist primarily of a nucleus in a bag with a tail, not much cytoplasm, but all cells receive an equal amount.

SpermatogenesisAll spermatozoa are equally available for

fertilization.

Sperm production begins at puberty.

Depending on the species, continues essentially throughout the adult life of the animal.

OogenesisMuch more interesting; occurs in the ovaries.

Depending on the species, meiosis initiates during prenatal development, but then is arrested (usually in Prophase II) until puberty.

Oogonium differentiates into a primary oocyte.

OogenesisPrimary oocyte undergoes meiosis I to form one

secondary oocyte and one polar body, which will not undergo further division.

The secondary oocyte receives the bulk of the cytoplasm.

OogenesisThe secondary oocyte divides during meiosis II to

form the ovum and a second polar body.

The result of meiosis in the female is one ovum and two polar bodies for each primary oocyte that enters meiosis.

Comparing Mitosis and MeiosisMitosis is a conservative process that maintains the genetic status quo

IN CONTRAST,Meiosis generates combinatorial variation through independent assortment and crossing-over (recombination)

Comparing Mitosis and MeiosisMitosis: One cell division resulting in two diploid

daughter cellsMeiosis: Two cell divisions resulting in four haploid

products …..Mitosis: One S phase per cell divisionMeiosis: One S phase for two cell divisions

Comparing Mitosis and MeiosisMitosis: no pairing of homologuesMeiosis: full synapsis of homologues at prophase I….Mitosis: normally, no crossoverMeiosis: at least one crossover per homologous pair…Mitosis: Centromeres divide at anaphaseMeiosis: Centromeres do not divide at anaphase I but do

divide at anaphase II

DNA Replication

DNA Replication

DNA Recombination(Crossing Over)