From time to time, lecture
notes may appear here
Lecture 1a
Science in General
1.
Based on your knowledge from other sources, links in the web
page, or other sources, review and be prepared to discuss :
The nature of science and the
scientific method
The
scientific meaning of ‘hypothesis’ and ‘theory’ (note that ‘theory’ as commonly
used has a different meaning in science, e.g. the theory of relativity, germ
theory, theory of evolution)
For a general
review check out the web page: http://undsci.berkeley.edu/article/0_0_0/whatisscience_03
(see other links in the course web page)
There are
misconceptions about what science is and is and isn’t. See the
What
constitutes a fair test in science?
Read: http://undsci.berkeley.edu/article/0_0_0/fair_tests_01
What is the nature of ‘proof’? Is it possible to prove something to be
true?
2.
What is the role of experimentation in science?
3.
How do scientists regard the supernatural?
Evolution
1.
Is evolution the same as Darwinism?
2.
Things
dating, archaea, epigenetics, ribozymes, Hox genes to name a
few. Can
you make a list
of 4 or 5 more?
4.
What role did Mendel play in
Natural
Selection
1. What is the
difference between Natural Selection, Evolution and
Darwinism?
2.
observations and 2
deductions:
Obs. 1 – All organisms have the
potential to increase exponentially in
population
size
Obs. 2 – Populations fluctuate over
time but never exhibit a
trend
toward continuous exponential growth
Ded
.
1 – Nature limits exponential growth by causing mortality (disease,
starvation,
crowding, competition etc)
Obs. 3 - In general, organisms are unique, each
varying from other others
in a range of measurable
characteristics; many of these
variations are
heritable, i.e. changes
can be passed on to
offspring
Ded.
2 - Individuals
who inherit variations which confer even a slight
benefit
in survival and reproduction compared to other
individuals
are more likely to survive and, and the
trait which
provided
the benefit will be passed on to the next generation
(natural
selection). Over time, the favorable
trait will increase in
the
population as alternate – less beneficial – traits decline and
disappear. This is evolution.
5.
The only requirements for natural selection are: (1) the trait under selection must be heritable
(2) The trait must provide a benefit which ultimately results in relatively
greater lifetime reproductive success than other individuals which do not
inherit the trait (3) The organisms bearing the trait must be capable of
reproduction
6.
periods. Complex structure could evolve from simpler
structures as long
as each
step conferred a fitness benefit, i.e. somewhat greater lifetime
reproductive
success.
HARDY-WEINBERG
The Hardy-Weinberg law is important because it defines the condition
under which no evolution will occur, i.e. under which gene frequencies will
remain unchanged from one generation to the next.
Be sure to know what those conditions are (random mating, large
population size, not selection, closed population)
Remember the basic formulas:
p2 + 2pq + q2 = 1 and p + q = 1
p = frequency of the dominant allele in the population
q = frequency of the recessive allele in the
population
p2 = frequency of homozygous dominant
individuals
q2 = freqency
of homozygous recessive individuals
2pq = frequency of heterozygous individuals
PROBLEM
Assume that eye color is determined by a
single liocus with two alleles. You have sampled a population
in which you know that the percentage of blue-eyed individuals [homozygous
recessive genotype (aa)] is
36%. Using that 36%, calculate the following:
Answer
You have sampled a population in which you
know that the percentage of the homozygous recessive genotype (aa) is 36%. Using that 36%,
calculate the following:
Check out this web page for other problems is you are interested.
http://www.k-state.edu/parasitology/biology198/hardwein.html
Sex Lecture 1 Lecture Notes
a. Still the primary mode in viruses, bacteria, unicellular protists, some
animals and plants (although most protists, animals and plants have sexual
reproduction in addition, i.e. Haploid/Diploid Cycles)
b. Major problems – all individuals are exact genetic copies of parents (with the exception of rare mutants)
c. About 1.5 billion years ago, an alternate form of reproduction appeared in unicellular eukaryotic organisms which allowed exchange of genetic material between similar organisms.
(1) This involved the temporary fusion of two individuals and the
reciprocal exchange of genetic material – the start of sex
(2) Evolution of meiosis occurred after the evolution of mitosis, i.e
The evolution of linear chromosomes and mitosis was a prerequisite for the evolution of meiosis and sex.
In many unicellular protists, life cycles involve an alteration of haploid and diploid stages.
(a). Both haploid and diploid stages have advantages
(b). Prior to the evolution of sex, the diploid condition could have been achieved
by duplication of the genome.
1. True sexual reproduction (involving meiotic exchange of gametes) appeared
first in unicellular Protists (eukaryotes), and probably involved the fusion of
individual cells, each acting as a gamete.
2. These cells were equal in size (Isogamy)
3. Although originally, any two cells probably could fuse (syngamy), at some
point early on, it appears that differences in cell surface chemistry evolved
such that only individuals with different surface cell chemistries would fuse.
These are called Mating Types
a) Generally, only two mating types occurs + (or recipient types) and –
(or donor types)
4. One possible advantage to the evolution of mating types is to minimize
inbreeding.
a) Individuals of the same mating type may be closely related
genetically.
b) Fusion of related individuals is more likely to produce double
recessive genotypes in which harmful recessive genes will be
expressed.
5. But why just two mating types? After all, this cuts the number of potential
mates in a population by half!
a) The answer my be the advantage of uniparental
inheritance of
cytoplasmic organelles.
b) Organelles such a mitochondria and chloroplasts are found only in the
cytoplasm
c) If organelles were inherited from both gametes, the zygote would
contain a mixture of genetically distinct organelles. (Remember, mitochondria
and chloroplasts have their own genomes)
d) This would present the possibility of intracellular competition between
organelles.
6. Evidence to support this hypothesis is provided by a group of ciliate protozoa
(Paramecium)
a) Unlike other protists, Paramecium has multiple mating types.
b) However, Paramecium has a unique mating system called Conjugation, in which cells line up and exchange haploid pronuclei through a small hole.
c) The hole is too small, and too ephemeral, to permit cytoplasmic organelles such as mitochondria from passing through.
d) In other words, Paramecium achieves uniparental inheritance by a different mechanism, and can thus evolve more than two mating types.
1. In general, multicellular organisms produce two categories of gametes, small
gametes (microgametes = sperm) and large gametes (macrogametes = ova)
2. This condition is called Anisogamy
3. A number of interesting hypotheses exist to explain the evolution of anisosgamy
a. Frequency Dependent Model - Assume that within a population of sexually-reproducing isogamous invividuals, a mutation for smaller gametes appeared.
b. The mutant individuals would be able to produce more gametes, fertilize more gametes, and gain a fitness advantage
c. The mutant allele should begin to spread through the population
d. However, as the mutant individuals became more common, the probability that small gametes would fertilize other small gametes would increase
e. These zygotes would have fewer resources that other zygotes, and would be less likely to survive (fitness decrease)
f. Under these conditions, a mutation in which small gametes fertilized only large gametes (and vice versa) – if it should appear – would be favored by selection
4. An alternate hypothesis – Hurst & Hamilton (1992)
a. As discussed above, since microgametes (sperm) are too small to contain
mitochondria in their cytoplasm, syngamy between a micro- and macrogamete does not entail the potential problems of mixed mitochondrial lineages in the zygote, i.e. uniparental inheritance of mitochondria is
guaranteed.
5. Global Implications of Anisogamy
a. Evolution of separate male and female strategies to maximize fitness (gender)
b.
Genomic Imprinting
and parent-Offspring Conflict
1) In pregnant humans, nutrients required by the fetus travel via spiral arteries in the
placenta.
2) Tissues around these arteries are invaded by cells from the fetus called cyrtotrophoblasts. These cells affect the arterial wall, thus reducing the mother’s ability to restrict blood flow to the fetus. ( Why would the mother wish to control this flow?)
3) Fetal cells produce Growth Factor II which facilitates the continued proliferation of
cyrtotrophoblasts. Only the paternally-derived copy of the gene for Growth Factor
II is expressed; not the maternal copy, i.e. the allele contributed by the father
promotes greater resource flow into the fetus from the mother. This is an
example of Genomic Imprinting. The opposite allele on the maternal
chromosome has been silenced.
4) Maternal cells around the arteries produce Growth Factor I, which acts to
neutralize Growth Factor II, thus partially counteracting the effect of Growth
Factor II
An interesting evolution-based hypothesis has been suggested that can account for these facts. The imprinting of the maternal allele may be a consequence of a conflict of interest between the mother and the father/fetus (both of which have a stake).
While it is obvious that the mother has a vested interest in the survival of her fetus, she may need to balance that current interest against the need to reserve energy and nutrients for future pregnancies. Thus, a mother’s allocation of maternal resources to the fetus may be balanced by the mother’s potential for future offspring, as well as the needs of current offspring. However – in most species - any future offspring may have a different father than the current fetus. Therefore, the father’s gene, inherited in the fetus, should promote the success of the current fetus, even at the expense of the mother, and her future offspring.