Biology Workshop (SM Sains Kubang Pasu)

Allele and Gene

A gene is a part of the DNA. Alleles on the other hand refer to different versions of the same gene. There are other more subtle differences between the two and this is what we are going to explore. 

• Genes are the different parts of the DNA that decide the genetic traits a person is going to have. Alleles are the different sequences on the DNA-they determine a single characteristic in an individual.
• Another important difference between the two is that alleles occur in pairs. They are also differentiated into recessive and dominant categories. Genes do not have any such differentiation.
• An interesting difference between alleles and genes is that alleles produce opposite phenotypes that are contrasting by nature. When the two partners of a gene are homogeneous in nature, they are called homozygous. However, if the pair consists of different alleles, they are called heterozygous. In heterozygous alleles, the dominant allele gains an expression.
• The dominance of a gene is determined by whether the AA and Aa are alike phenotypically. It is easier to find dominants because they express themselves better when they are paired with either allele.
• Alleles are basically different types of the same gene. Let me explain this to you in this way- If your eye colour was decided by a single gene, the colour blue would be carried by one allele and the colour green by another. Fascinating, isn’t it?
• All of us inherit a pair of genes from each of our parents. These genes are exactly the same for each other. So what causes the differences between individuals? It is the result of the alleles.
• The difference between the two becomes more pronounced in the case of traits. A trait refers to what you see, so it is the physical expression of the genes themselves. Alleles determine the different versions of the genes that we see. A gene is like a machine that has been put together. However, how it will works will depend on the alleles.

Both alleles and genes play an all important role in the development of living forms. The difference is most colourfully manifest in humans of course! So next time you see the variety of hair colour and eye colour around you, take a moment and admire the phenomenal power of both the gene and the allele!

 Summary

1. Genes are something we inherit from our parents - alleles determine how they are expressed in an individual.

2. Alleles occur in pairs but there is no such pairing for genes.

3. A pair of alleles produces opposing phenotypes. No such generalisation can be assigned to genes.

4. Alleles determine the traits we inherit.

5. The genes we inherit are the same for all humans. However, how these manifest themselves is actually determined by alleles.

Industrial melanism in Biston betularia

1.  Industrial melanism - the phenomenon

Many moths in Britain come in two different colours, a lighter "natural" form, and a darker, melanic form.

The melanic form is in all ways similar to the natural form except that it produces a much greater amount of melanin, the pigment that gives its wings their dark colouration. 

In Biston betularia, Kettlewell and his group have performed crosses that have demonstrated that a single gene controls the difference between natural and melanic morphs.

2.  Historical records

In the last 150 years, the relative preponderance of the two morphs has changed dramatically.

Old collections from the early 1800's show that the pepper morph was far and away the most abundant morph. 

Melanic morph was collected only very rarely.

Beginning in the early to mid 1800's, however, melanic form increased in abundance dramatically, until today, in some areas virtually all moths are melanic.

There has thus clearly been a dramatic change in gene frequencies, i.e. evolution has occurred. 

3.  Observation:  the change in morph frequencies corresponded with the onset of the industrial revolution in Britain.

One consequence of the industrial revolution was that the smoke and soot put out by all of the factories that sprung up across Britain caused a darkening of the tree trunks in many areas, particularly near urban industrial centers. 

Originally, tree trunks had been covered with light-coloured lichens, but after the industrial revolution, these lichens and the tree trunks they covered became dark in these areas; many likens were killed.

4.  Kettlewell's hypothesis:  Because moths spend a great deal of time during the day resting on tree trunks, Kettlewell reasoned that they are probably exposed to a great deal of predation by birds and other animals.  It would therefore benefit a moth to be cryptically coloured, so that it will blend in well with the background of the tree trunk on which it rests.

Individuals that were more cryptically colored would tend to escape notice by predators to a greater extent, and thus would tend to have a survival advantage over non-cryptically coloured individuals. 

Kettlewell postulated that before the industrial revolution, the pepper form blended in with the light-colored background of tree trunks, whereas the black morph was conspicuous, leading to selection against the melanic morphs.  This genotype would thus be held at very low frequency. 

With the change in tree trunk color associated with industrialization, however, the melanic forms became cryptically colored and the pepper forms became conspicuous.  Under such situations, the rare melanic mutants would enjoy a survival advantage and increase in frequency until the pepper forms were eliminated from the population.

Visual inspection of the degree of crypsis on dark and light tree trunks supports this hypothesis.   

5.  Experimental test of the hypothesis. 
I. Compare survival of melanic and pepper moths.

Capture-Mark-Release-Recapture experiment. Released several hundred marked individuals of both morphs into two types of woodlands:                  
 --  One woodland near a big city; polluted; trunks darkened with soot.
 --  One woodland more rural, relatively unpolluted; tree trunks not darkened.

Recaptured using caged females emitting pheromones. 

Reasoning:  if dark morphs have survival advantage in polluted woods, should recapture more dark morphs than pepper morphs.  By contrast, if pepper morphs have survival advantage in unpolluted woods, should recapture  more pepper moths there. 

Results:

                                          %Recaptured
                    Woodland    Melanics    Pepper
                    Urban            27.5           13.0
                    Rural               6.3           12.5

This experiment showed that the melanic form did indeed enjoy a survival advantage in polluted woodlands, while the reverse was true in unpolluted areas.  However, Kettlewell still had not shown that this differential survival was caused by differential susceptibility to predation. 

6.  Experimental test of the hypothesis. 
II. Differential predation

Placed recently-killed moths of each morph on tree trunks in the two types of woodland. Sat in blind and observed what happened to moths placed out.  In particular, counted the number of individuals of each morph eaten by birds. 

Results

                                            No. of moths eaten by birds
                    Woodland            Melanics        Pepper
                    Urban                     15                  43
                    Rural                     164                 26

Interpretation:  Kettlewell's hypothesis is confirmed.  In the polluted environment, more pepper morphs are eaten, while in the unpolluted environment, more melanic morphs are eaten.

7.  Summary:

Industrial melanism is genetically controlled by a single locus in B. betularia. 

Populations have undergone evolutionary change in color pattern. 

That change is consistent with the interpretation that it was due to natural selection, in that there is differential survival of the genotypes caused by differential predation on a particular background. 

Results confirm qualitative prediction of equation for gene frequency change.

8.  Additional point

Industrial melanism is seen in more than 70 species of British moths, and all show patterns similar to that seen in B. betularia.

At least one prediction based on Kettlewell's work has come true: since the imposition of pollution control devices on many of Britain's factories in the 1950's, pollution has decreased markedly in many areas.  As a result, many of the formerly polluted woodlands have returned to their original condition, in which the colour of the tree trunks is light and mottled.  As would be expected from Kettlewell's work, the melanic forms that were once so prevalent in these areas have almost disappeared.

(see H.B.D. Kettelwell.  1973.  Industrial Melanism.  Oxford Univ. Press, Oxford, U.K.)

Diabetes Mellitus and Diabetes Insipidus

The two types of diabetes : diabetes insipidus and diabetes mellitus

They differ in many ways. Though they share common name, ‘diabetes’, the reasons behind them and most of the symptoms are different. Diabetes mellitus is the most common of the two, as it is a lifestyle disease that affects metabolism in our body. The increased incidence of sedentary life, tensions, and decrease in physical activity are mostly to be blamed, though some other reasons such as auto-immune disease also are causes. Some severe head injuries, tumours, or certain diseases can result in diabetes insipidus.

Here is more about diabetes insipidus and diabetes mellitus and the differences between them.

What is diabetes insipidus?

Due to some injuries or viral diseases, the hypothalamus or pituitary gland get damaged and might be rendered unable to produce the hormone vasopressin or ADH. In some, the kidneys might have defect or be damaged due to certain reasons resulting in inability to respond to vasopressin/ADH. This lack of vasopressin/ADH or inability to respond to vasopressin causes the body to lose water through excessive urination. This is known as diabetes insipidus.

What is diabetes mellitus?

Diabetes mellitus varies from diabetes insipidus mainly in the hormone involved. When it comes to diabetes mellitus, the hormone involved is insulin, secreted by pancreas, which is absorbed by the cells in our body as a message to use glucose present in the blood. When pancreas is unable to secrete insulin or when the cells in our body develop resistance to insulin, the glucose in the blood will not be utilised. This is known as diabetes mellitus.

What are the differences between diabetes mellitus and diabetes insipidus?

• The Hormones Involved

In diabetes insipidus, it is the lack of vasopressin /ADH or inability of kidneys to respond to it, which is synthesised by hypothalamus in the brain and released by pituitary gland present nearby.

Where as in diabetes mellitus, the hormone insulin, which is secreted by the cells in pancreas present near the stomach, is either deficient or the body is unable to respond to it.

• What is in excess?

In those who are suffering from diabetes insipidus, excess urination results in increasing the concentration of salts or electrolytes present in the body. This is known as hypernatraemia.

In diabetes mellitus, since the body cannot process the glucose present in blood, there is either excess glucose present in the blood or very low levels of glucose present in blood because of physical activity or insulin intake, though this is when there is no proper control of blood sugar and health.

• The Reasons for Polyuria

Polyuria is one of the symptoms of both diabetes mellitus and diabetes insipidus.

But, the reason for the symptom polyuria in diabetes insipidus is the kidneys do not either receive the anti-diuretic hormone (ADH) or they are unable to respond to it. This inhibits the kidneys ability to reabsorb water into bloodstream to prevent dehydration.

The symptom polyuria in diabetes mellitus is due to the presence of excess glucose in blood, a situation known as hyperglycaemia. The kidneys then try to discard this excess glucose through urination, resulting in polyuria.

• Other Differences in Symptoms

In diabetes insipidus, the symptom polydipsia is due to frequent urination or because of damage to thirst mechanism, whereas, in diabetes mellitus, it only occurs when there is hyperglycaemia. Polyphagia is a symptom of diabetes mellitus, but, is not seen in diabetes insipidus.

Though it may seem difficult to cope with diabetes and be optimistic about the treatment, there are many in the world, suffering from diabetes insipidus and diabetes mellitus, who have taken their lives into their hands and started working on themselves to get healthy and better quality of living. Proper nutrition and good physical activity, with treatment and medication in the right time can always make life happier and easier.

Ta ta......

Biology Workshop (SMK Bandar Sg. Petani)

Biology Workshop (SMK Bukit Gambir)

Biology Workshop (SMK Tunku Abdul Malik)

Program Peningkatan Prestasi Akademik Biologi STPM Kedah 2012

Paper 1
http://www.scribd.com/doc/102906636

Paper 2
http://www.scribd.com/doc/102906738

Mark scheme (P1)
 http://www.scribd.com/doc/106649899


Mark scheme (P2)
http://www.scribd.com/doc/106650002

Good luck.....

Biology Workshop - SMK Naka, SMK Bukit Payong, SMK Kuala Nerang (Dewan Makan SMK Naka)

Biology Workshop for Collegians (Centennial Auditorium)

Reproductive cycle of the human female

The reproductive cycle of the human female.  The figure above shows how (c) the ovarian cycle and (e) the uterine (menstrual) cycle are regulated by changing hormone levels in the blood, depicted in parts (a), (b), and (d). The time scale at the bottom of the figure applies to parts (b)–(e).

The hormones at the top levels of control of this dual cycle are the same brain hormones that control the male reproductive system. These hormones are gonadotropin–releasing hormone (GnRH), secreted by the hypothalamus, and the gonadotropins follicle–stimulating hormone (FSH) and luteinising hormone (LH), secreted by the anterior pituitary. The concentrations of FSH and LH in the blood control the production of two kinds of steroid hormones that are made in the ovaries: oestrogen (actually a family of closely related hormones) and progesterone. The ovarian cycle of hormone production in turn controls the uterine cycle of endometrial growth and loss. The outcome is that ovarian follicle growth and ovulation are synchronised with preparation of the uterine lining for possible implantation of an embryo. 

The Ovarian Cycle.    
1 The cycle begins with the release from the hypothalamus of GnRH, which 
2 stimulates the pituitary to secrete small amounts of FSH and LH. 
3 The FSH (true to its name) stimulates follicle growth, aided by LH, and 
4 the cells of the growing follicles start to make oestrogen. Notice in the figure that there is a slow rise in the amount of oestrogen secreted during most of the follicular phase, the part of the ovarian cycle during which follicles are growing and oocytes maturing. (Several follicles begin to grow with each cycle, but usually only one matures; the others disintegrate.) The low levels of oestrogen inhibit secretion of the pituitary hormones, keeping the levels of FSH and LH relatively low.

The levels of FSH and LH, however, shoot up sharply when 
5 the secretion of oestrogen by the growing follicle begins to rise steeply. Whereas a low level of oestrogen inhibits the secretion of pituitary gonadotropins, a high concentration has the opposite effect: It stimulates the secretion of gonadotropins by acting on the hypothalamus to increase its output of GnRH. 
6 You can see this response in the figure as steep increases in FSH and LH levels that occur soon after the increase in the concentration of oestrogen, indicated in the figure. The effect is greater for LH because the high concentration of oestrogen also increases the sensitivity of LH–releasing cells in the pituitary to GnRH. By now, the follicles can respond more strongly to LH because more of their cells have receptors for this hormone. The increase in LH concentration caused by increased oestrogen secretion from the growing follicle is an example of positive feedback. The LH induces final maturation of the follicle. 
7 The maturing follicle develops an internal fluid–filled cavity and grows very large, forming a bulge near the surface of the ovary. The follicular phase ends, about a day after the LH surge, with ovulation: The follicle and adjacent wall of the ovary rupture, releasing the secondary oocyte.

8 Following ovulation, during the luteal phase of the ovarian cycle, LH stimulates the transformation of the follicular tissue left behind in the ovary to form the corpus luteum, a glandular structure. (LH is named for this “luteinising” function.) Under continued stimulation by LH during this phase of the ovarian cycle, the corpus luteum secretes progesterone and oestrogen. As the levels of progesterone and estrogen rise, the combination of these hormones exerts negative feedback on the hypothalamus and pituitary, inhibiting the secretion of LH and FSH. Near the end of the luteal phase, the corpus luteum disintegrates, causing concentrations of estrogen and progesterone to decline sharply. The dropping levels of ovarian hormones liberate the hypothalamus and pituitary from the inhibitory effects of these hormones. The pituitary can then begin to secrete enough FSH to stimulate the growth of new follicles in the ovary, initiating the next ovarian cycle.

The Uterine (Menstrual) Cycle.    
The hormones secreted by the ovaries—oestrogen and progesterone—have a major effect on the uterus. Oestrogen secreted in increasing amounts by growing follicles signals the endometrium to thicken. In this way, the follicular phase of the ovarian cycle is coordinated with the proliferative phase of the uterine cycle. Before ovulation, the uterus is already being prepared for a possible embryo. After ovulation, 
9 oestrogen and progesterone secreted by the corpus luteum stimulate continued development and maintenance of the endometrium, including enlargement of arteries and growth of endometrial glands. These glands secrete a nutrient fluid that can sustain an early embryo even before it actually implants in the uterine lining. Thus, the luteal phase of the ovarian cycle is coordinated with what is called the secretory phase of the uterine cycle.

10 The rapid drop in the level of ovarian hormones when the corpus luteum disintegrates causes spasms of the arteries in the uterine lining that deprive it of blood. The upper two–thirds of the endometrium disintegrates, resulting in menstruation—the menstrual flow phase of the uterine cycle—and the beginning of a new cycle. By convention, the first day of menstruation is designated day 1 of the uterine (and ovarian) cycle. Menstrual bleeding usually persists for a few days. During menstruation, a fresh batch of ovarian follicles are just beginning to grow.

Cycle after cycle, the maturation and release of egg cells from the ovary are integrated with changes in the uterus, the organ that must accommodate an embryo if the egg cell is fertilized. If an embryo has not implanted in the endometrium by the end of the secretory phase of the uterine cycle, a new menstrual flow commences, marking day 1 of the next cycle. Later in the chapter, you will learn about override mechanisms that prevent disintegration of the endometrium in pregnancy.

In addition to the roles of oestrogen in coordinating the female reproductive cycle, this hormone family is responsible for the secondary sex characteristics of the female. Oestrogen induces deposition of fat in the breasts and hips, increases water retention, affects calcium metabolism, stimulates breast development, and influences female sexual behaviour.

Menopause    
After about 450 cycles, human females undergo menopause, the cessation of ovulation and menstruation. Menopause usually occurs between the ages of 46 and 54. Apparently, during these years the ovaries lose their responsiveness to gonadotropins from the pituitary (FSH and LH), and menopause results from a decline in estrogen production by the ovary. Menopause is an unusual phenomenon; in most species, females as well as males retain their reproductive capacity throughout life. Is there an evolutionary explanation for menopause? Why might natural selection have favoured females who had stopped reproducing? One intriguing hypothesis proposes that during early human evolution, undergoing menopause after having some children actually increased a woman′s fitness; losing the ability to reproduce allowed her to provide better care for her children and grandchildren, thereby increasing the survival of individuals bearing her genes.

Preparing for Biology Exam

Biology exams can seem intimidating and overwhelming to biology students. The key to overcoming these obstacles is preparation. By learning how to study for biology exams you can conquer your fears. Remember, the purpose of an exam is for you to demonstrate that you understand the concepts and information that have been taught. Below are some excellent tips to help you learn how to study for biology exams. 

Get Organised 

An important key for success in biology is organisation. Good time management skills will help you to become more organised and waste less time preparing to study.

Items such as daily planners and semester calendars will help you to know what you need to do and when you need to have it done. 

Start Studying Early 

It is very important that you start preparing for biology exams well in advance. I know, I know, it is almost tradition for some to wait until the last minute, but students who implore this tactic don't perform their best, don't retain the information, and get worn out. 

Review Notes 

Be sure that you review your notes before the exam. You should start reviewing your notes on a daily basis. This will ensure that you gradually learn the information over time and don't have to cram. You must know how to take notes. 

Review the Biology Text 

Your biology textbook or reference book are wonderful sources for finding illustrations and diagrams that will help you visualise the concepts you are learning. Be sure to reread and review the appropriate chapters and information in your book. You will want to make sure that you understand all key concepts and topics. 

Get Answers To Your Questions 

If you are having difficulty understanding a topic or have unanswered questions, discuss them with your teacher. You don't want to go into an exam with gaps in your knowledge. 

Quiz Yourself 

To help prepare yourself for the exam and find out how much you know, give yourself a quiz. You can do this by using prepared flash cards or taking a sample test. You can also use online biology games and quiz resources. 

Find a Study Buddy 

Get together with a friend or classmate and have a study session. Take turns asking and answering questions. Write your answers down in complete sentences to help you organise and express your thoughts. 

Attend a Review Session 

If your teacher holds a review session, be sure to attend. This will help to identify specific topics that will be covered, as well as fill in any gaps in knowledge. Help sessions are also an ideal place to get answers to your questions. 

Relax 

Now that you have followed the previous steps, it's time to rest and relax. You should be well prepared for your biology exam. It's a good idea to make sure you get plenty of sleep the night before your exam. You have nothing to worry about because you are well prepared.

Lastly, if donno, tanya ur teacher la....

Inheritance of Sex–Linked Genes

In addition to their role in determining sex, the sex chromosomes, especially X chromosomes, have genes for many characters unrelated to sex. A gene located on either sex chromosome is called a sex–linked gene , although in humans the term has historically referred specifically to a gene on the X chromosome. (Note the distinction between the terms sex–linked gene, referring to a gene on a sex chromosome, and linked genes, referring to genes on the same chromosome that tend to be inherited together.) Sex–linked genes in humans follow the same pattern of inheritance that Morgan observed for the eye–color locus in Drosophila. Fathers pass sex–linked alleles to all of their daughters but to none of their sons. In contrast, mothers can pass sex–linked alleles to both sons and daughters.

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The transmission of sex–linked recessive traits.  In this diagram, the superscript A represents a dominant allele carried on the X chromosome, and the superscript a represents a recessive allele. Imagine that this recessive allele is a mutation that causes a sex–linked disorder, such as color blindness. White boxes indicate unaffected individuals, light–coloured boxes indicate carriers, and dark–coloured boxes indicate individuals with the sex–linked disorder

 

If a sex–linked trait is due to a recessive allele, a female will express the phenotype only if she is a homozygote. Because males have only one locus, the terms homozygous and heterozygous lack meaning for describing their sex–linked genes (the term hemizygous is used in such cases). Any male receiving the recessive allele from his mother will express the trait. For this reason, far more males than females have sex–linked recessive disorders. However, even though the chance of a female inheriting a double dose of the mutant allele is much less than the probability of a male inheriting a single dose, there are females with sex–linked disorders. For instance, colour blindness is a mild disorder inherited as a sex–linked trait. A colour–blind daughter may be born to a colour–blind father whose mate is a carrier. However, because the sex–linked allele for colour blindness is relatively rare, the probability that such a man and woman will mate is low.

A number of human sex–linked disorders are much more serious than colour blindness. An example is Duchenne muscular dystrophy , which affects about one out of every 3,500 males born in the United States. The disease is characterised by a progressive weakening of the muscles and loss of coordination. Affected individuals rarely live past their early 20s. Researchers have traced the disorder to the absence of a key muscle protein called dystrophin and have mapped the gene for this protein to a specific locus on the X chromosome.

Haemophilia is a sex–linked recessive disorder defined by the absence of one or more of the proteins required for blood clotting. When a person with haemophilia is injured, bleeding is prolonged because a firm clot is slow to form. Small cuts in the skin are usually not a problem, but bleeding in the muscles or joints can be painful and can lead to serious damage. Today, people with haemophilia are treated as needed with intravenous injections of the missing protein.

Biology Workshop (ASTECH)

Biology Workshop (SMK Agama Kedah)

Biology Workshop (Sekolah-sekolah Daerah Langkawi di SMK Mahsuri)