Transcript (4) Hydrogen Bonding, Meiosis & Meitosis and Colorblindness

It’s Thursday, yeah!
One more day until the weekend,
so take heart…
First, of course we have some stuff
to cover…
• Lets recap last week because the concept
of hydrogen bonding and interactions is
pivotal to later learning and DNA reactions
• So, as I said… quick hydrogen bond recap
Ahh the perfect bond, Super strong yet
plays well with others
Again, not all of this is
relevant, just pay
attention to the bonding
and dipole interactions,
also note how the huge
disparity in boiling
points shows you how
very strong hydrogen
bonds can be en-mass
and how much energy
(heat energy in this
case) it takes to bust
them up.
Thanks You Tube…
But also remember, it is important for the DNA double
helix to realign -come back together again- post
replication. This is why hydrogen bonds fit the bill and
want to reassemble once they have been broken open.
Experiments and Paper Write-up Recap
• Many of you wrote about Lycopodium powder.
This floats on the surface of water because of
the high surface tension of water, Yes! Since
there is no attraction between the lycopodium
powder molecules and the water molecules, the
powder is indeed hydrophobic. For this reason,
lycopodium powder molecules tend to stay
together, repelling the water and forming a
water-resistant "glove" around your hand.
What we neglected to tell you…
• Is that it is also
delightfully
flammable.
Surface Tension
• Many of you wrote
about surface tension.
• It is all about
hydrogen interactions
and arrangements.
Remember that this world is not onedimensional though, and surface tensions
and molecular interactions operate in many
“upside-down” ways as well.
Mitosis and Meiosis
Lab Manual Objectives
• Understand purpose and key steps of
mitosis and meiosis, including the
differences
• Examine meiotic fates of genes
• Understand the following terms: allele,
dominant, recessive, sex-linked, etc
Sex-Linked
• Some traits/phenotypes exhibit
themselves due to sex linked inheritance
• Females are most responsible for most of
these phenotypes. Why?
• Take a look at the X and Y chromosomes.
Heck, why don’t we take a look at
all of the chromosomes.
Speaking of sex linked…
• Why does all of this matter
anyways?
Because
you will
finally
understand
why, at the
molecular
level,
human
Hallowe’en
costumes
like these
exist !
Images swiped from C.G.
Dividing and Deducing
• Taking care of genetic information; figuring
it out from a standing start
Why teach genetics & genetic
concepts?
• Well, it’s a lovely example of the Scientific
Approach in action
• It also highlights how apparent complexity
can usually be broken down to orderly
simplicity
• Plus Jen likes it, a lot.
Lets start with the lingo
•
Gene: A stretch of DNA that represents all the
information for a product as well as when and where
to make the product.
•
Allele: A version (or flavor) of a gene; two alleles of
the same gene my differ by a nucleotide or dozens of
them--generally a small number.
•
Dominant/recessive: Two alleles enter; one allele
leaves (which version manifests in the organism)
– NOT which version is more common!
Lets use some of those words in a
different way
• Gene: irreducible particle of inheritance
e.g. eye color in humans
• Allele: alternative forms of a gene; for
simple Mendelian traits, each gene has
two alleles (one dominant, one recessive)
e.g. brown eyes vs. blue eyes.
Dominance
• The genotype of a simple Mendelian
trait is comprised of two copies of each
gene - one from each parent. Each
carries 2 alleles. Each of the 2 could be
dominant or recessive.
Egg
sperm
Onto Mitosis & Meiosis
• NOVA says it best
• This short animation should shed a little
light on some of the key differences (and
sameness) between the two processes.
Where does mitosis happen?
• There are two kinds of cell division: mitosis and meiosis..
meiosis exclusively happens in sex cell namely sperm
cell and egg cell.. they produce haploids (half the
chromosomes number)
• Mitosis happens on all cells of the body aside from sex
cell (sperm and egg cell)... in other words they happen to
somatic cells (all cells of the body aside from sex cells)...
they produce diploids (they have complete set of
chromosomes... in humans, we have 46 chromosomes)
including the sex chromosomes.
Your DNA is packed into
your chromosomes so
amazingly and efficiently.
Forming sister chromatids
that hold it all in!
Mitosis Manually
• What cells ‘do’ mitosis?
• What’s the goal/purpose of this thing
called ‘mitosis’?
• So what must the first step be? Do it.
• Now what must be achieved?
– Any half? If not, how pick the appropriate
half?
• How do your final results compare with
starting?
Mitosis vs. Meiosis
• Where is mitosis happening in your body?
•
- Somatic cells, replacement of the 1050 trillion cells!
– (10^14 = 100 000 000 000 000)
• Where is meiosis happening in your body?
•
- testes if you are male
•
- for females, precursor eggs are
suspended in prophase I prior to birth
when ovaries are forming
Mitosis gone wrong
2nd most common cause of death
• When cell cycle malfunctions - cell reproduction at wrong
time / place
• Benign tumors at original site in body
• Deranged cell cycle = cancer = Malignant tumors
– Carcinoma - external/ internal coverings of body
– Sarcoma - support tissues (bone, muscle)
– Leukemia, lymphoma - blood-forming tissue cancers
Slash, burn, poison!
An ounce of prevention…
– Quit smoking & over-sunning, Get adequate
exercise & fiber + fat diet
– Exams:
– Skin & oral - physical
– Breast - self
– Prostate - rectal
– Cervical - well-woman
– Testicular - self
– Colon – colonoscopy
– And have safe sex gosh darned it (not that it’s
relevant here… but it’s relevant nonetheless)
M & M Differences?
• Recombinatory (sexual) reproduction vs.
clonal (asexual) reproduction
• Haploid (n) daughter cells vs. diploid (2n)
daughter cells
More?
• Two division events vs. One division event
• One DNA replication for two division
events vs. DNA replication for each
division event
• Four daughter cells vs. Two daughter
cells
Dominance
• The phenotype, physical expression of
genotype, determined by dominance of
genotype’s alleles.
• If allele is dominant, then phenotype is
expressed regardless of other allele’s state.
• Recessive phenotype is only expressed
when organism possesses two copies of
recessive allele
An Example: Eyes
• What does it mean genetically when we
say ‘brown eyes are dominant’?
• Why should that be so? What do brown
alleles got that blue do not?
• Think about this, we will return to it
shortly.
What’s my
genotype?
In an alternate universe
Bb
x
http://www.rotten.com/library/bio/entertainers/actors/brad-pitt/
bb
If Jen is Bb & Brad Pitt is bb: assuming they
mated
B
b
b
Bb
bb
b
Bb
bb
M
F
What is the chance that we will have blue eyed offspring?
Furthermore (and I actually have green
eyes, I just like to be next to Brad Pitt)
• Blue eyes arise from a DNA change that
prevents creation of melanin in the eye
specifically
• Mutation appears identical in all blueeyed folks, suggesting single origin
• Popular press account*
– It’s not a ‘mutation’; it’s a mutation
• On green eyes
Mutations are not always beneficial
though right?
Examples
Color blindness – Sex linked
Illustration
• Interesting illustration
of some types of color
blindness.
Monohybrid cross
In this example, both organisms have the genotype Bb. They can
produce gametes that contain either the B or b alleles. (It is conventional
in genetics to use capital letters to indicate dominant alleles and lowercase letters to indicate recessive alleles.) The probability of an individual
offspring having the genotype BB is 25%, Bb is 50%, and bb is 25%.
Some genetics food for thought
• Why is genetic diversity important? Why
doesn’t everyone just have the same
allele for a gene?
• Why is inbreeding generally bad?
Meiosis: the other cell division
• How much are you ‘like’ your ma & pa?
• How much of your genome should you
give your child if he/she is not
uniparental?
Why do my kids look (and act) so
different than me?
Note: Other Kid refuses to have photo in powerpoint – she is the fun police 
Differences and sameness
Me: Freckles, very serious individual indeed,
Green/Hazel eyes…
Teenager: Brown eyes,
way smart & studious…
Bubble monster:
Hazel eyes, very
bubbly and master
of all athletics…
Meiosis I: Separate the Homologues
But wait..there's more! Meiosis II:
Separate the Sister Chromatids
Exercise
Good clean fun
– Whip out the sister chromatids
– Now, make a copy--b/c that’s the way it
happens
– Next, pair the pairs: maternal & paternal
contributions pair
– Recombine (randomly)
– Now what?
– When you’re a gamete, go mate with a
classmate… oh come on, just do it…
Seeing and believing
• Mitosis: Turning an onion into a squash
• Meiosis: Prepared grasshopper testes
Genes on chromosomes
• Linked/Linkage: Referring to whether
genes are tethered to one another
by virtue of being ‘close’ on a
chromosome
Gameter: Super fun on the
computer
•
•
•
Linkage refers to the ‘me-too’ behavior of 2
genes strung together by a relatively small
number of nucleotides
Postulate: The closer two nucleotides are the
(less/more) likely a recombination event is to
take place between them
Thus, the closer two GENES are on a
chromosome, the (less/more) likely it is that the
parental state of the chromosome will be passed
on intact to offspring
Got That?
Fire it up
• Load Gameter
• Interface walk-through: designing the
•
•
•
parentals
Automatic crosses
Manual crossing over (does not re-build
the chromosomes)
Doing homework
More to know
•
Allele: A version (or flavor) of a gene; two
alleles of the same gene my differ by a
nucleotide or dozens of them
– Common symbolism: A vs. a or BLU vs. blu (etc.!)
•
Homozygous: ‘same-zygous’ = having
identical alleles (AA, aa)
•
Heterozygous: ‘different-zygous’ = having
different alleles (Aa)
Butterflies
•
•
•
•
If NOT logged in, tutorial in main lab walks you
through ‘mating and sorting’
Once logged in, choose ‘Find the Genotype’
After answering, hit submit; you’ll see score and
be offered a hint if score ≠ 100 (and all 3
answered)
You can store @ any time by submitting, but no
hints til done
Thinking through it
•
Load x_plorer: (an exercise to guide you in thinking
through upcoming homework)
•
•
•
Simultaneously consider two alternative
hypotheses about dominance (left half; right
half)
Work through BOTH cases until you have an
ordered set of tests (algorithm) to distinguish
(i.e. rule one OUT)
Watch the lavender box for ‘what to do next’
Room 420
Clean up
Room 430
Room 450
Room 460
Leave em the way you found them…
Homework… of great importance
• Homework
• Complete StructViewer if you haven’t
• Gameter: Solve + explain
• Mendelstar: ‘Find the genotype’ + explain