LIFESCI 2A03 Lecture Notes - Lecture 1: Testability, Repeatability, Amputation

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Life Sci 2A03 Test 1 Material
Lecture 1
Characteristics of Science
1. Science is based upon empirical knowledge – observations that are made
2. Commitment to rationality/ natural explanations
3. Repeatability (and reliability)- need to be confirmed so must be consistent and
reliable
4. Testability: must be able to design an experiment that tests theory
5. Commitment to use of experimentation – intervention into natural processes to
observe effects
6. Generality of principles – must be able to apply to all systems
Scientific Model
1. Define/Outline the Problem
2. Form hypothesis
3. Test hypothesis (make observations or experiments)
4. Organize and Analyze Data
5. Does data support hypothesis? If not, new experiment and analysis
6. Conclusions
7. Communicate results
Case Study: Human Chromosome Count
Painter reported only having 48 chromosomes in human cell using serial sectioning, this
number was simply accepted, since it was tested using the same technique, for 33 years.
However, in the 1950s there were new techniques where you squashed the cell and spread
out the metaphase chromosomes and treatments to preserve the chromosomes. They were
placed in hypotonic treatment to allow chromosomes to spread out and then treated with
colchicine to stop them at the metaphase stage and Tijo and Levan counted 46
chromosomes.
What went wrong?
An observation is not enough, the data was ambiguous and clouded observation; people
had a bias opinion; Painter’s sample wasn’t large enough – he was taking samples from a
single man
In 21st century we are in the genomic era, in 2003 it was estimated 24 847 genes in the
Human Genome
Lecture 2 – A Hypothesis
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Life Sci 2A03 Test 1 Material
A hypothesis is a proposal that makes a prediction. Application of scientific method
allows one to test the hypothesis
The hypothesis:
Provides tentative explanations that account for observations;
Lead to predictions about the result of intervention
Predictions can be verified or refuted by analyzing data
Formulation and testing of hypothesis is basis of scientific or rational inquiry
Inductive: summarize a set of observations and serve to provide a prediction of unseen
events i.e. this ice is cold; therefore all ice must be cold
Deductive: using general to go to a single item i.e. if all green apples are sour, then this
green apple is sour
You use deductive reasoning in order to reject a hypothesis
If… Then … this is called deductive syllogism
We mainly test the null hypothesis
If your results are inconsistent with your hypothesis, you reject the hypothesis; if you
obtain a true prediction, then you failed to reject the hypothesis (never say you proved the
hypothesis)
Null Hypothesis:
Not just the opposite of the hypothesis – stated in the following way: There is no
significant difference between two sets of results
Difference in observations between control group and experimental group
Observations of 2 groups in 2 different conditions
A set of predicted results and the observed results
Case Study: Ice Cream Headaches
Hypothesis: The rate at which you eat ice cream affects whether you will experience an
ice cream headache
Null hypothesis: There is NO EFFECT of the rate of eating ice cream on the incidence of
ice cream headaches, or, There is NO DIFFERENCE in the occurrence of headaches
between 2 groups, one in which ice cream is eaten slowly and other in which ice cream is
eaten quickly, or, there is NO STATISTICAL DIFFERENCE in the observed effects
between the 2 groups
Experiment: Green dot- had to eat their ice cream slowly and red dot had to eat their ice
cream quickly – tested this on 145 students
Results: 27% reported headaches in red dot group and 9% in green dot group
Are these results significantly different? Is there variation other than random variation?
We reject the null hypothesis – original hypothesis is consistent with data or we fail to
reject the null hypothesis – didn’t detect a difference but there may be one
Case Study 2: Old men and big ears
Hypothesis: As you grow older, your ears get bigger
Null Hypothesis: As you grow older, your ears remain the same size, etc.
Reject or Fail to reject null hypothesis? Reject
Conclusion in article: as we get older, ears get bigger. Positive correlation
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Life Sci 2A03 Test 1 Material
Do you agree with conclusion? NO because only a select few people people were looked
at at one point in time, we cannot conclude with this information that our ears grow with
age, this data only shows that there is a correlation with age and ear size.
Lecture 3 – Regeneration
The regrowth of lost or destroyed parts or organs
In plants, we see a technique called plants cutting – cut the root off and place into water
and it will regrow the roots – i.e. in carrots, you separate cells and get a collection of cells
called amendium which then can form an entire plant
In mustard seeds, you can see regeneration taking place, you use a fluorescent protein in
the cell – since it is the same timing and it looks the same as growing, might be the same
gene that is involved in this process
In animals, few invertebrates demonstrate bidirectional regeneration- can cut two halves
and it’ll make a whole again – called clonal reproduction – seen in animals with radial
symmetry
Bidirectional Regeneration: ability to regenerate whole bodies from small tissue
fragments – hydra that is cut in half will regenerate and become 2 different hydra that
look exactly the same and then will grow
Classic example of this is Planaria, which is a non-parasitic worm that can regenerate
What happens?
1. Muscular contraction to limit size of cut surface
2. Thin wound epithelium forms over surface – prevents infections from occurring
3. Accumulation of undifferentiated cells called NEOBLASTS in the blastema –
neoblasts migrate to cut surface; if we prevent them from doing so, regeneration
will not take place since they are essential to this process
4. Growth and differentiation of blastema – a collection of undifferentiated cells is
called a blastema
In Planaria, if it is cut 3 ways, the head portion will regenerate the body and tail; the body
will regenerate the head and tail and the tail will regenerate the body and head
Blastema: mass of undifferentiated cells capable of growth and regeneration into organs
or body parts
Neoblasts: regenerative cells within the blastema; act as stem cells for growth and
regeneration – the blastema cells in the planaria; they are able to divide, differentiate sand
are always present
Function? When an amputation occurs, neoblasts are used to regenerate and they are
recouped (restocked) so there is always the same amount
Hypothesis: If the neoblasts are distributed across the body, any part we cut should be
able to regenerate – can use neoblasts as a model for all stem cells
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Document Summary

What happens: muscular contraction to limit size of cut surface, thin wound epithelium forms over surface prevents infections from occurring, accumulation of undifferentiated cells called neoblasts in the blastema neoblasts migrate to cut surface; if we prevent them from doing so, regeneration will not take place since they are essential to this process, growth and differentiation of blastema a collection of undifferentiated cells is called a blastema. Takes about 40 days to form new limb: amputation, wound healing epithelial cells rapidly migrate from circumference of limb to plane of amputation 12 to 24 hours to form epidermal covering key to organization of regenerating cells and rest of process cannot happen without this, dedifferentiation cell undergoes loss of specialization and resemble embryonic cells allows for proliferation and repatterning of cells and then new limb, budding (early, medium, late) beginning of growth dedifferentiated cells accumulate at the end of stump and from blastema, which initiates growth.

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