Upload
lamkhue
View
215
Download
0
Embed Size (px)
Citation preview
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 [email protected]
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)