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Review for Exam 2 Friday 30th March Evolution • Charles Darwin (1809 – 1882) - “on the origin of species by means of natural selection.” • Had two main hypotheses. – Branching descent – living species come from a species that lived in earlier times. This explains common inheritance. – Natural selection – explains that parents with genotypes that favor survival and reproduction leave more offspring than other parents. Therefore, these genetic traits become dominant in a given population. • Both of these hypotheses have been tested thousands of times without being falsified. Biological Evolution • First true cells were prokaryotic. – Eukaryotic cells evolved later, followed by the other kingdoms. • Biological evolution is a change in life forms that has taken place in the past and will take place in the future. –Adaptation is a characteristic that makes an organism able to survive and reproduce in an environment. Natural Selection • • • • • Variation in population Variation inheritable Some individuals survive and reproduce better than others Survival and reproduction are tied to variation in traits among individuals (non-random) Therefore, these genetic traits become dominant in a given population. Industrial Melanism • Powerful demonstration of natural selection. • Darker colored peppered moths were discovered in areas of the UK with high levels of pollution. – Known as melanic moths • First found in 1890s at the height of the industrial revolution. Remember genetic mutation? • Either a single nucleotide substitution or an addition or a deletion in the genetic material controlling moth skin color occurred – Altered the open reading frame – May be caused by the pollution itself • The result was an ever increasing population of black peppered moths in certain areas. Central Dogma of Molecular Biology • DNA holds the code • DNA makes RNA • RNA makes Protein • If pollution altered the genetic material of peppered moths, then the protein product (skin color) would be altered! Evidence for Branching Descent • Homologies: The construction of family trees in based on shared similarities and gene sequences. • Darwin noted the similarities of forearms in mammals. • Darwin wondered on why mammals have the same bones in the same relative positions. • All had a ratio of bones from five (fingers) to two (lower “arm” –radius and ulna) to one (upper “arm” humerus). Evidence for Branching Descent • Convergence – Similarities that result from common ancestry should also be similar at a smaller level of detail. – Should grow from the same source tissue • Convergence is an evolutionary phenomenon in which similar adaptations evolve independently in lineages not closely related. • Bat wings are similar in structure to whale flippers, the human arm and the front legs of all mammals. Post - Darwin • Steven Jay Gould : • Punctuated Equilibrium – Species remain static for long periods of time and then changes abruptly. • The new species begins as a small isolated population on the geographic periphery of the original species. • The small size of the isolated population allows it to undergo rapid change – Therefore producing a new species • Once new species becomes successful, overcomes original species and the original species becomes extinct. Why is it so difficult to design an AIDS vaccine? • Natural selection – Mutation – Variation – Selection pressures • Transmission from other hosts Application of principles of natural selection creationism • Bible-based creationists – Use a biblical account of creation – Reject any scientific account that conflicts with scripture • Intelligent-design creationists – Work within the framework of science to find evidence of design in nature – State that biological systems are so complex that only an intelligent (and benevolent) designer could have made them. • Theistic evolutionists – Believe that God created the universe and all life – Evolution is in fact Gods creative process and part of the plan. Human Variation • Genetics is the study of biological traits. These traits are coded for in genes, which are parts of chromosomes. • An Allele is a variant of a gene. These can be dominant or recessive, and these are the basis of inherited traits, both structural and behavioral. • Chromosomes exist as homologous pairs. Human Variation • Somatic Cells - Non-sex Cells. Contain a full compliment of chromosomes. Characteristic to their species. Referred to as the diploid number of chromosomes. • Gametes - Sex Cells. Cell which carry genetic information for sexual reproduction. Contain one half the compliment of chromosomes characteristic to their species. Referred to as the haploid number of chromosomes. Human Variation • Arms and legs are longer and thinner in warm areas of the planet – shorter and thicker in cold regions. • Conserves heat in cold regions by reducing surface area • Skin pigmentation is darker the nearer the equator to protect the skin from UV. Polygenic Inheritance • The additive effects of two or more genes on a single phenotype Polygenic inheritance Single trait (e.g., skin color) Multiple genes Visual Summary 9.5 Polygenic Inheritance • Three genes inherited separately • The dark-skin allele for each gene (A, B, and C) contributes one “unit” of darkness to the phenotype and is incompletely dominant to the other alleles (a, b, and c). aabbcc (very light) AaBbCc Eggs AABBCC (very dark) AaBbCc Sperm • An AABBCC person would have very dark skin • An aabbcc person would have very light skin Figure 9.22 Why does this happen? Figure 7.4 Both type A and type B blood have specific carbohydrates which are on the surface of the blood cells. AB blood has both carbohydrates on the surface of the blood cells o blood has no carbohydrates Carbohydrates are: N-Acetylglucosamine, galactose and fucose Also known as antigens Why does this happen? Figure 7.4 Controlled by three alleles Allele A – dominant has info for making antigen A Allele B – dominant has info for making antigen B Allele o – recessive produces neither antigen AA & Ao gives rise to A type blood BB & Bo give rises to B type blood AB is co-dominant - AB type blood oo is recessive – o type blood • The genetics of the Rh factor Another blood grouping system independent of ABo – the Rh-factor – Again, three genes (alleles): located very close together on the same chromosome. • First C & c, second D & d, third E & e • Unlike the ABo system there is no co-dominance, c, d, and e are recessive to C, D, and E. • ccddee is known as Rh-negative. All others Rhpositive. Malaria – an agent of natural Selection • Sickle Cell Anemia • Controlled by intermediate phenotypes at a ratio of 1:2:1 • Red blood cells are not concave • Normal Hemoglobin (HbA). Sickle cell (Hbs) • HbA-HbA-normal Hbs-Hbs – sickle cell • HbA-Hbs- have the trait • Therefore, incomplete dominance. Malaria – an agent of natural Selection - Remember mutations? Any change in the nucleotide sequence of DNA Normal hemoglobin DNA Mutant hemoglobin DNA mRNA mRNA Normal hemoglobin Glu Sickle-cell hemoglobin Val Figure 10.21 Figure 7.10 A small change in a gene can have many phenotypic consequences. • Testis--paired gonads within scrotum, sperm and steroids produced here. • Epididymis--tightly coiled duct where sperm maturation occurs. • Vas Deferens--delivers sperm through abdomen to ejaculatory duct. • Urethra--duct through penis where sperm and urine exit • Semen--seminal fluid, contains sperm, fluid and ATP producing nutrients (sugars). • Prostate Gland--adds fluid to semen. • Seminal Vesicles-contribute nutrients to semen. • Bulbourethral gland-contributes mucoid Hormonal control of testes • Hypothalamus- secretes gonadotropinreleasing hormone (GnRH). – Stimulates the anterior pituitary to release • • • • Follicle-stimulating hormone (FSH) Promotes sperm production & release of Inhibin Luteinizing hormone (LH)*** ***Sometimes called interstitial cell-stimulating hormone (ICSH). This stimulates the production of testosterone. • All these hormones are involved in negative feedback that maintains the fairly constant production of sperm and testosterone. Female Reproductive System • Ovaries--produce eggs and steroid hormones. • Oviducts--conduct the egg to the uterus--fertilization occurs here. • Uterus--Womb, where we are developed. • Cervix--Opening to Uterus. Female Reproductive System • Clitoris--Female analog of the penis. This is also contains erectile and sensory tissue. • Vagina--site of sperm deposition, birth canal, exit for menstrual flow. • Vulva--External folds of skin that protect the vagina. Hormonal Control of Ovaries • Hypothalamus- secretes gonadotropin-releasing hormone (GnRH). – Stimulates the anterior pituitary to release • Luteinizing hormone (LH) • Follicle-stimulating hormone (FSH) • FSH Stimulates the follicle to produce estrogen. • LH Stimulates the corpus leuteum to produce progesterone. • Estrogen and Progesterone maintain uterus and help regulate the hypothalamus. negative feedback !!!!!!!! Ovarian cycle Ss s Days 1-13- FSH secretion Day 14 – OVULATION LH SPIKE Days 15-28 – LH increases corpus luteum forms Progesterone high Uterine Cycle s Days 1-5- Menstruation Day 6-13 – Endometrium rebuilds Days 15-28 –Endometrium thickens mucoid glands develop and secrete Fertilization • Egg-– Corona Radiata: Cells from follicle that nourished egg in ovary. – Zona Pellucida: layer that covers plasma membrane--will form fertilization envelope – Plasma Membrane: cell membrane around egg. – Egg Nucleus: contains DNA Fertilization • Sperm-– Head: Contains sperm nucleus and acrosome. – Acrosome: Contains enzymes. – Mid Piece: Contains Mitochondria – Tail: Flagella made from Microtubules How the atmosphere formed Figure 19.2 Stanly Miller’s Experiment -1952. Amino acids, simple sugars, and most of the building blocks for DNA and RNA were produced. An energy source is required for the formation of these molecules. These expts, repeated thousands of times have produced so many biologically important products that the conclusion is not in doubt All molecules important to life where made in the primitive atmosphere Structure of the atmosphere • Hint: • Learn about the layers of the atmosphere! CO2 andFigure Global Warming 19.9 •The greenhouse effect: • The process in which the absorption of infrared radiation by an atmosphere warms a planet. •Without these greenhouse gases, the Earth's surface would be up to 30° C cooler. •CO2 is used in photosynthesis to make carbohydrates. CO2 levels rise at night and fall during the day naturally. Due to the photosynthetic activity of plants •CO2 is released during respiration or when organic compounds are burned. CO2 andFigure Global Warming 19.9 •An increase of CO2 decreases the amount of heat which can escape through the atmosphere. •Thus the temperature of the Earth increases. •This has many effects. •Warmer Ocean layers. •Atmospheric shifts. •Warmer surface temperatures •2005 was hottest year on record. The Chloroplast • Membranes contain chlophyll and it’s associated proteins – Site of photosynthesis • Have inner & outer membranes • 3rd membrane system – Thylakoids • Stack of Thylakoids = Granum • Surrounded by Stroma – Works like mitochondria • During photosynthesis, ATP from stroma provide the energy for the production of sugar molecules The chemical reaction of photosynthesis is driven by light • The initial reaction of photosynthesis is: – CO2 +H2O (CH2O) + O2 – Under optimal conditions (red light at 680 nm), the photochemical yield is almost 100 % – However, the efficiency of converting light energy to chemical energy is about 27 % • Very high for an energy conversion system Summary of light reactions • Plants have two reaction centers: – PS-II • Absorbs Red light – 680mn • makes strong reductant (& weak oxidant) • oxidizes 2 H2O molecules to 4 electrons, 4 protons & 1 O2 molecule • Mostly found in Granum – PS-I • • • • Absorbs Far-Red light – 700nm strong oxidant (& weak reductant) PS-I reduces NADP to NADPH Mostly found in Stroma The Carbon reactions • The NADPH and ATP move into the liquid environment of the Stroma. • The NADPH provides H and the ATP provides energy to make glucose from CO2. • The Calvin cycle thus fixes atmospheric CO2 into plant organic material. Photorespiration • Occurs when the CO2 levels inside a leaf become low – This happens on hot dry days when a plant is forced to close its stomata to prevent excess water loss • If the plant continues to attempt to fix CO2 when its stomata are closed – CO2 will get used up and the O2 ratio in the leaf will increase relative to CO2 concentrations • When the CO2 levels inside the leaf drop to around 50 ppm, – Rubisco starts to combine O2 with Ribulose-1,5bisphosphate instead of CO2 The C4 carbon Cycle • This is a biochemical pathway that prevents photorespiration • C4 leaves have TWO chloroplast containing cells – Mesophyll cells – Bundle sheath (deep in the leaf so atmospheric oxygen cannot diffuse easily to them) • C3 plants only have Mesophyll cells • Operation of the C4 cycle requires the coordinated effort of both cell types – No mesophyll cells is more than three cells away from a bundle sheath cells • Many plasmodesmata for communication How the rest of plant works • Roots – absorb water from the soil as well as many mineral nutrients • Xylem – transports water from the roots to the rest of the plant • Phloem – transports sugars made in the leaves via photosynthesis to the pest of the plant • Leaves – Site of gas exchange CO2 brought in and O2 out. Have structures called Stomata which also control water loss. Plant cell in hypotonic solution • Flaccid cell in 0.1M sucrose solution. • Water moves from sucrose solution to cell – swells up –becomes turgid • This is a Hypotonic solution - has less solute than the cell. So higher water conc. • Pressure increases on the cell wall as cell expands to equilibrium Plant cell in Isotonic solution • Water is the same inside the cell and outside • An Isotonic solution has the same solute than the cell. So no osmotic flow • Turgor pressure and osmotic pressure are the same Plant cell in hypertonic solution • Turgid cell in 0.3M sucrose solution • Water movers from cell to sucrose solution • A Hypertonic solution has more solute than the cell. So lower water conc • Turgor pressure reduced and protoplast pulls away from the cell wall Water transport • Transpiration • Evaporation of water into the atmosphere from the leaves and stems of plants. • It occurs chiefly at the leaves while their stomata are open for the passage of CO2 and O2 during photosynthesis. • Transpiration is not simply a hazard of plant life. It is the "engine" that pulls water up from the roots to: – supply photosynthesis (1%-2% of the total) – bring minerals from the roots for biosynthesis within leaf – cool the leaf. Increasing crop yields Figure 11.13 • To feed the increasing population we have to increase crop yields. • Fertilizers - are compounds to promote growth; usually applied either via the soil, for uptake by plant roots, or by uptake through leaves. Can be organic or inorganic • Have caused many problems!! • Algal blooms pollute lakes near areas of agriculture Chemical pest control Figure 11.17 • Each year, 30% of crops are lost to insects and other crop pests. • The insects leave larva, which damage the plants further. • Fungi damage or kill a further 25% of crop plants each year. • Any substance that kills organisms that we consider undesirable are known as a pesticide. • An ideal pesticide would:– – – – Kill only the target species Have no effect on the non-target species Avoid the development of resistance Breakdown to harmless compounds after a short time Good Luck on Friday!