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