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Dominant and Recessive Alleles Experiment

Discussion
Part A
The number of dominant genes was constant from one generation to the next. It remained at a number of 50 alleles considering that all Bengal tigers with the dominant allele (H), survived to pass on the gene. On the other hand, the frequency of the dominant allele increased over the ten generations. The frequency of the dominant allele during the first generation was 0.50, but by the tenth generation, the frequency increased to 0.93. This was because all the offspring with the homozygous recessive genotype weren’t able to survive. As generations passed by, the gene pool grew smaller, the number of the recessive alleles also decreased, however the number of dominant alleles remained the same; resulting in an increase of the “H” allele frequency.
The number of recessive genes generally decreased from one generation to the next. However, there were a few cases where it stayed the same; if no offspring with the homozygous recessive genotype was produced in that generation. In generation one, the number of recessive alleles was 50, but by the tenth generation, the number decreased significantly to only 4. Similarly, the frequency of the recessive allele decreased as well, considering that only the homozygous recessive cubs died while the homozygous dominant cubs survived to reproduce. In the beginning, the frequency number was 0.50, by the tenth generation the number was to 0.07. The frequency of the recessive allele would be zero permanently for all future generations, if the recessive gene became extinct. All members of the population would be homozygous dominant in the absence of the recessive allele; hence the frequency would be zero as there would be no chance of producing heterozygous or homozygous recessive offspring within the population. In this case, the dominant allele would be considered as a fixed allele with a consistent frequency of one (“Fixed Allele,” 2014).
As emigration and immigration came into play, the gene frequency of “H” and “h” in the tiger population either increased or decreased. As the population accepted new members, the frequency of the alleles increased considering that additional genes were being added to the existent gene pool. Moreover, as members of the population left the group, the frequencies decreased considering that as the size of a population decreased; its gene pool would shrink.
Part B
According to the Hardy-Weinberg principle, it was expected that the derived population would contain equivalent proportions of the dominant allele (red candy) and the recessive allele (green candy). Considering that the frequency of the dominant and the recessive allele were the same, 0.50; (p q = 1), the two alleles should have equal probability of getting chosen to be a part of the derived population. Therefore in a population of 20 genes, 10 should be dominant and 10 should be recessive, while in a population of four genes, two should be dominant and the other 2 recessive.
The actual results differed from the expected results. It was predicted that in the smaller populations, there would be equal amounts of the dominant and recessive alleles considering that the two started off equally with the same frequency number; equal potential of getting chosen. However, the actual results revealed that it was impractical for the number of the dominant and recessive alleles to be equal in the smaller populations. Out of eight derived populations of 20 genes, only two consisted of equal amounts of “H” and “h” alleles. Furthermore, out of the eight derived populations of four genes, only one had the expected result with two dominant and two recessive alleles. In all the small populations of 20 genes, the amount of dominant to the amount of recessive were fairly close to each other (ex. 8:12), if not precisely the same. However, for the small populations of four genes, there were two extreme outcomes where either the dominant or recessive allele was absent in the population resulting in the presence of a fixed allele (ex: 0:4).
The expected results or the theoretical probability of the allele frequencies was only an effective method of estimating the results based on the given information. It was a calculation derived from a theory, and therefore it did not always represent the actual results. However, it did provide an idea of the likelihood for a situation to occur. For example, the subject would know that the allele frequencies for the majority of the derived populations should be close to 0.50.
It could be possible for a small population to produce a large population in one generation, however highly unlikely, also it would depend on the kind of organism. In this case, the life span of a tiger was approximately 20 years old and it took about 16 weeks for cubs to be born. Furthermore, tigers did not have a fixed mating season and females could produce one to seven cubs per litter (“Tiger Reproduction,” 2014). Therefore, it was possible for a small population to produce a large number of offspring, however not all will survive. The more cubs the females would have to take care, the higher the mortality rate of the offspring. Hence, it would be extremely improbable for all the offspring produced to survive long enough to reproduce.
A population bottleneck would present similar fluctuations as a genetic drift. A bottleneck effect could be defined as a drastic decrease in the size of a population due to human activities, an inability to reproduce offspring fit enough to survive, or natural disasters such as earthquakes, floods, and droughts (“The Genetic Variation,” 2013). This would further limit the variation in the gene pool of the population and could even cause the population to become extinct, considering that the smaller the population, the higher the chance for inbreeding to occur in the population. The process of inbreeding would result in the accumulation of the hidden, unwanted and harmful alleles in the population. Furthermore, the population’s ability to adapt to fluctuating environments and new selection pressures would decrease due to the loss of genetic variation within the population (“Population Bottleneck,” 2014). Another form of the bottleneck effect is the founder effect; where a small group from a population decided to establish a new population separated from the main population resulting in a great loss of genetic variation (“Population Bottleneck,” 2014). Hence, it would be extremely difficult for a small population to be able to produce a large population in a few generations.
Part C
The percentage of each allele gave a better idea of the genetic make-up of a population considering that it simplified the total number to 100. Therefore, a percent could be defined as a portion of every 100, knowing that the total number would always be constant; it’d be easier to visualize the genetic make-up in one’s mind. For example, the use of a pie charts. Furthermore, percentages were comparable; the higher number always showed that certain gene dominated a large portion of the population and approximately how large (ex. ½ of the population). On the other hand, the numbers of each allele did not give the observant much immediate information about the genetic make-up of the population. The subject would have to calculate the total number of alleles first, in order to achieve a vague idea of which gene was the most frequent in the population. However, when comparing the genetic make-up between the original population and after the bottleneck effect, the use of percentages gave a lot more information than the numbers of allele considering that the total number of alleles differed in the two scenarios.
For most of the alleles, the allelic frequency increased after the bottleneck effect, while for others, it decreased. The alleles that experienced an increase in their allelic frequency were orange, red, blue, pink and purple. The alleles that showed a decrease were white and green. The allelic frequency for yellow stayed the same considering that the allele was extinct.
The alleles left in the bottle were wiped out of the population and weren’t included in the small population. The small group could have been geographically separated from the main population or the few survivors of the population after a catastrophe such as an earthquake.
The death of a small number of individuals in the large population would have little effect on the gene pool of the population. However, if those certain individuals possessed a specific gene that was rare in the population, then it would have a larger effect on the gene pool and the allelic frequencies of that population. For example, the rare gene could gradually become extinct since it was already low in quantity in the population.
A few long-term consequences of the bottleneck effect on a population included; an increased chance of becoming extinct, a loss of genetic variation, a loss of rare alleles, a greatly limited gene pool, and lastly a reduced potential to adapt to new environments or new selection pressures such as climate changes and a change in resource abundance (“Population Bottleneck,” 2014).
Conclusion
It could be concluded that gene frequencies and the size of the gene pool of a population could have a huge influence on evolution and the survival probability of the population. Gene frequencies of a population are greatly affected by environment pressures. Over time, the environment pressures would cause the favoured gene to increase in frequency and the disfavoured to decrease or in rare cases, become extinct. This would result in the formation of a population that has been adapted to the new environment and became more physically fit to survive in the new environment. Furthermore, the gene pool of a population is significantly affected by genetic drift and the bottleneck effect of a population. It was proven in the lab that the resulting number of genes after a genetic drift was in fact by chance. The bottleneck effect was characterized by a drastic decrease in a large population. Hence in both situations, the gene pool of the population would experience a sharp reduction in size. This could lead to the extinction of the population due to the lack of genetic variation caused by inbreeding. Though it could be possible for the small population to produce a large population, it would be highly likely.
Error
An error that had occurred while conducting the experiment was that the candies and gumballs may not have been mixed properly. A few times, the subject forgot to shake the bag of candies before drawing out two alleles. This could have produced biased results as more of one type of candy might have ended up on the top, which increased its chance of being chosen. Additionally the percentage of the alleles did not add up to 100% after the bottleneck effect. This was because the whole percentage weren’t taken into account as all the results were rounded to only two decimal places.

Homeostasis: Coordination and Response

SABRINA PACE-HUMPHRES
Homeostasis, Co-ordination and Control and the Excretory system
What is homeostasis?
Homeostasis is the condition of equilibrium (balance) in the body’s internal environment due to the constant interaction of many of the body’s regulatory processes. The body strives to maintain balance and therefore is constantly adjusting. Homeostasis is dynamic in this respect and is controlled through the nervous and endocrine systems, running through a path which includes three elements: receptor, control centre and effectors. In response to changing environmental conditions, equilibrium can shift among points in a narrow range thus making life maintenance compatible. Each bodily structure – from cells to systems – contributes to keeping the internal environment within normal limits.

How is body temperature maintained? Why this is necessary for the organism?
Humans must maintain constant core temperature of 37°C. If exceeded (above 45°C) cellular protein becomes inactive/unable to function. Below 0°C cellular water freezes and ice crystal growth affects membranes/kills the organism.
Shell temperature of peripheral systems e.g. near skin, arms and feet and Core temperature at which core organs (heart/lings etc) work efficiently is constantly monitored.
The hypothalamus deals with temperature regulation. It compares ideal temperature to what the rest of the body is experiencing. Its preoptic control centre evaluates information from receptors in the mouth, skin, spinal cord and brain which detect temperature changes. If change occurs the control centre sends signals to effectors who commence response processes – vasodilatation or vasoconstriction – that change the situation reinstating normal levels.
A negative feedback loop ensures that changes are reversed and set back to normal. Receptors ïƒ control centre ïƒ effectors work in a constant cycle for temperature maintenance.
If temperature is too high vasodilatation occurs – blood vessels leading to the skin capillaries dilate to reduce temperature. Core blood is sent near skin surface and cooled by outside temperature via heat radiation. On return to the core its cooler and temperature lowered. Sweating causes core temperature decrease through water evaporation, although water loss in the wrong environment can lead to fatal dehydration.
Vasoconstriction – the narrowing of blood vessels leading the capillaries – occurs when the core temperature low. Blood flow to peripheral parts is reduced. Vessel constriction maintains core temperature by reducing cold blood from periphery areas. To combat low core temperatures a person may start to shiver, producing a muscular waste product – heat.
A vasoconstriction negative is that muscles can’t function under a certain shell temperature. If immersed in extremely cold water. and vasoconstriction activated, muscular ability is restricted due to reduced blood flow causing paralysis. Homeostasis which aims to preserve core temperature can be fatal.
Behavioural mechanisms like looking for a warmer environment/adding clothing are voluntary but not automatic as they are still regulated by the hypothalamus.
Water is important for homeostasis, how are water levels maintained within the body and why is it important to do so?
Water makes up tissues and blood. It’s used to distribute nutrients and oxygen around our systems and carry away waste products. Water equilibrium is necessary for survival and is ingested from food, drink and respiration and lost through sweat, urine and breathing.
Kidneys are responsible for maintain water equilibrium. As blood flows through them, water content is measured. If blood contains the correct amount, kidneys expel water (evidenced by pale urine). If they detect not enough water, they reabsorb it from circulating blood (evidenced by dark – concentrated – urine).
Intracellular cell dehydration is monitored by Osmoreceptors located in Hypothalamus. They monitor the body’s water balance and, when they sense cellular dehydration, these receptors becoming dehydrated too (shrivel and deform).
The control centre – hypothalamus – detects osmoreceptor dehydration and makes adjustments by sending a message to the pituitary gland to produce/release Anti-Diuretic Hormone (ADH).
The function of ADH is to lessen excretion of water by causing kidney nephrons to increase their water permeable ability. When a signal is received from hypothalamus the Pituitary Gland releases ADH which travels to the kidneys via blood. Hypothalamus ïƒ Pituitary Gland ïƒ Kidneys ïƒ Osmoreceptors form the homeostatic negative feedback loop controlling water balance.
Increased cell dehydration leads to increased ADH released into blood passing the kidneys. In parallel, if osmoreceptors indicate the body’s water balance is normal (by swelling), the hypothalamus communicates to the pituitary gland that little/no ADH is needed, the effect being that kidneys expel more dilute urine.
Extracellular dehydration relates to overall blood volume and is monitored by sensors in the kidneys. When they detect a volume change they secrete rennin into blood which causes vessel constriction and, by reacting with angiotensin, this leads to a thirst sensation/need for salt. For example if a person is injured and looses blood they will feel thirsty even through cells are not dehydrated. Satiety sensors determine whether there’s enough water in the system to replenish cells/blood even when water has not reached all parts.
Insulin and Glucagon are homeostatic hormones: how is this the case and why are they necessary?
The endocrine system controls and coordinates biological systems through homeostasis via the production and release of chemical messengers called hormones.
A hormone is a chemical signal to re-prioritise cell activities. It’s a mediator molecule that’s released by one part of the body but regulates cells in other parts of the body. Endocrine Glands secrete hormones into interstitial fluid surrounding secretory cells. From this fluid, hormones diffuse into blood capillaries to be carried by blood to target cells throughout the body where said hormones exert their effects by binding to specific cell receptors.
An example of endocrine system homeostasis is shown in the maintenance of blood sugar levels. The pancreas – and endocrinal gland – is responsible for this as it produces and releases Insulin and glucagon which increases/reduces glucose levels. As can be seen below, each hormone opposes the action of the other, producing antagonistic effects.
Glucagon increases blood glucose levels when it falls below normal limits (hypoglycaemia) while insulin lowers the levels when it’s too high (hyperglycaemia). The level of blood glucose controls secretion of glucagon and insulin via negative feedback as shown below.
Hypoglycaemia stimulates secretion of glucagon from alpha cells of pancreatic islets ïƒ Glucagon acts on liver cells, accelerating the conversion of glycogen into glucose and promoting formation of glucose from lactic acid/certain amino acids ïƒ hepatocytes release glucose into blood more rapidly, blood glucose rises. If blood glucose continues to rise, the high level inhibits the release of glucagon (negative feedback).
High blood glucose (hyperglycaemia) stimulates secretion of insulin by beta cells of pancreatic islets ïƒ Insulin acts on various cells to accelerate facilitated diffusion of glucose, speeds conversion of glucose into glycogen, increase cellular uptake of amino acids, speeds synthesis of fatty acids, slows conversion of glycogen into glucose and slows formation of glucose from lactic/amino acids. Blood glucose levels then fall. If glucose levels drop below normal it inhibits release of insulin (negative feedback) and stimulates glucagon release.
The endocrine system – via the Pituitary Gland, Thyroid Gland, Adrenal Gland, Pancreas, Kidneys and the Reproductive Organs Ovaries (F) and Testes (M) – helps to regulate and maintain various body functions including responses to stress and injury, growth and development and birth and lactation by producing and releasing hormones to maintain homeostasis mainly by using negative feedback mechanisms such as that shown above.
Neural control centres in the brain control endocrine glands. The main neural control centre being the hypothalamus. This control centre sends messages to the Pituitary Gland (master gland) which, in turn, releases hormones that regulate body functions.

The functions of the subdivisions within the nervous system and, in the case of certain answers, their relationships to each other
Brain receives information, interprets it and guides the response.
Cerebrum controls memory, personality and conscious thought. Sensors receive information from receptors/pass to other brain regions for analysis/action. Motor area consists of motor neurons which, when stimulated, send impulses for skeletal muscle movement.
Cerebellum receives information from the sensory systems, spinal cord and brain regions for motor movement regulation. Co-ordinates posture and balance. Important for learning motor behaviours.
Spinal cord nerves provide ‘command and control’ routes for information transmission to limbs/organs. Provides route for sensory signals to the brain/way out for motor signals from it.
Somatic system is responsible for movement of voluntary muscles and the reflex arc process. Carries nerve impulses back/forth between the CNS, skeletal muscles, skin and sensory organs.
Sensory neurons convey information to CNS from receptors in head, body wall and limbs and from vision, hearing, taste and smell receptors.
Motor neurons conduct impulses from the CNS to skeletal muscles only. Under conscious control.
Autonomic system sensory neurons convey information from receptors located in visceral organs to the CNS. Motor neurons conduct nerve impulses from the CNS to smooth muscle, cardiac muscle and glands. Involuntary.
Sympathetic system neurons increase heart rate. Helps support exercise emergency actions, ‘fight or flight’ responses
Parasympathetic system neurons reduce heart rate. Take care of ‘rest or digest’ activities.

The similarities between the endocrine system and the nervous system as well as the differences.
Endocrine system
Nervous system
Similarities
Maintain homeostasis.
Work together to coordinate functions of all body systems.
Regulate biological processes inside an organism.
Differences
Hormone signal transmission is slower (seconds to hours to days) but action functions are longer lasting.
Nerve impulses are quicker (milliseconds) but action functions are shorter.
Signals are sent via chemicals (hormones).
Signals are sent via nerve impulse.
Effects are widespread throughout the body.
Localised effect
Formed of a collection of glands.
Formed of a collection of neural cells.
System organs are not physically connected. Anatomically discontinuous.
Cells are connected. Whole system is continuous.
Use circulatory system to transmit the signal.
Use neurons to transmit the signal.
Acts on all types of body cells.
Acts on specific muscles and glands.
Hormones delivered to tissues of the body through blood.
Neurotransmitters released locally in response to nerve impulses.
Hormones usually act upon cells far from site of release. Binds to receptors on or in target cells.
Act upon cells close to site of release, at synapse, binds to receptors in postsynaptic membrane.
Target cells throughout body.
Target muscle (smooth, cardiac and skeletal) cells, gland cells and other neurons.
Action onset is seconds to hours to days.
Action onset is usually within milliseconds.

What organs are involved in the excretory system and what structures do they have to carry out this role, use annotated diagrams as part of the answer
Key excretory system organs are the liver and kidneys.
The liver fulfills a range of processes including metabolism of proteins, fats, carbohydrates and bilirubin (produced when blood cells die) which is excreted through bile. During protein metabolism for ATP production, nitrogen removal from amino/nucleic acids produces amonia. The liver changes toxic amonia to a less toxic chemical called urea. It’s then transported to the bloodstream and removed by the kidneys.
The kidneys are sophisticated machines. Waste and water excreted from them forms urine which flows along the ureter to the bladder for storage/secretion. Kidneys contains 1-2 million nephrons – functional units that perform excretion and reabsorotion.
Nephron structure

Blood travels down the renal aorta to the kidneys and enters the Glomerulus – a network of capillaries responsible for blood filtration – where it’s squeezed through capillaries at high pressure allowing filtrate (including small ions like sodium and glucose) to pass into Bowman’s Capsule. Filtrate then travels through the Proximal Convoluted Tube and materials the body doesn’t want to lose – such as glucose, sodium, acids and some water – is reabsorbed using an active transport mechanism. Filtrate then enters the Loop of Henle. This hair-pin shaped structure uses active transport as a mechanism in its descending and ascending parts to remove sodium ions out of the filtrate, allowing for more effective reabsorption at the collecting duct. Filtrate then enters the Distal Convoluted Tubule where more calcium, sodium etc is reabsorbed. Waste products and excess water which is left travels to collecting ducts that send, what is now urine, down the ureter to the bladder for storage and secretion.
The lungs through diffusion of carbon dioxide excreted through breathing and the skin, through excretion of sweat which includes waste materials (urea, water) are also considered part of the excretory system.
Bibliography
Abpischools.org.uk, (2015). ADH and control of the water balance – ABPI – Resources for Schools. [online] Available at: http://www.abpischools.org.uk/page/modules/homeostasis_kidneys/kidneys6.cfm?coSiteNavigation_allTopic=1 [Accessed 21 Jan. 2015].
Akitarescueoftulsa.com, (2015). [online] Available at: http://www.akitarescueoftulsa.com/nephron-diagram-unlabeled/ [Accessed 26 Jan. 2015].
Bbc.co.uk, (2015). BBC – GCSE Bitesize: Water balance. [online] Available at: http://www.bbc.co.uk/schools/gcsebitesize/science/add_ocr_pre_2011/homeostasis/waterbalrev1.shtml [Accessed 27 Jan. 2015].
Education Portal, (2015). Somatic Nervous System: Definition, Function

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