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by
Roche A. Samy
The teachers in the Junior High Schools can also use these plans directly or modify to the students’ levels and needs.
The aim here is to attract students initially and to hold their interest, while slowly introducing the terms, vocabulary and thought-provoking discussion questions without turning them off.
Genetics is only one section of biology and can be prEsented within a week or two and the curiosity of students are brought into focus in the development of this unit.
The search for Nature’s secrets can be an exciting story if presented in an orderly manner. The subject can be introduced with a sequence of events that builds on mendel’s experiments with Pea Plants, leading to an understanding of basic, genetic mechanisms—sex determination, gene function and mutation. The students learn that Mendel concluded from his experiments that traits from both parents are passed on to the next generation of offsprings and that there are dominant and recessive factors for each trait.
What Mendel noted as factors are now called genes. These genes are located on the chromosomes which are found in the nuclei of the cells.
With the aid of models and hands-on experience, students are taught that the chromosomes are made up of long, coiled chemical chains known as DNA. During meiosis and mitosis, DNA is duplicated to make it possible for chromosomes and their genes to be transferred to new reproductive cells and body cells.
Vocabulary and genetic terms can be introduced slowly-heredity, genotype, phenotype, homozygous, heterozygous, sex determination. (xx and xy chromosomes) sex linked traits in humans, etc.
The curriculum unit is divided into 5 capsule lessons; each of which is introduced with the aid of some attention-getting pictures, models, photos, diagrams, slides, videos, demonstrations or activity.
This will turn the students on so that motivation can be generated by relating the information from the lesson to the students’ self-interest. The students’ natural curiosity about how human heredity works should be discussed fully. Further discussions and prepared debates on topics such as environment versus heredity should be encouraged.
- 1. Probing students’ knowledge of identical twins, lively discussions can be initiated.
- 2. Using various color-blindness charts, projection slides or diagrams, color-blindness can be surveyed and discussed.
- 3. Blood typing kits may be available from some biological supply houses. These can be used to determine blood types of students.
- 1. List the heredity factors that influence the traits of an organism.
- 2. Explain the terms heredity, genes, genetics, dominant and recessive.
- 3. Explain what a Punnett Square is in relation to Probability.
- 4. Give an analogy of heredity factors in an animal and in a human being. (ex. Animal-Short—horn Cattle, rr=Pure Red. ww=Pure White(p), rw=Hybrid Roan(F); incomplete dominance in Short—horn Cattle). (ex. Human being-Show picture or photo or slide of twins and explain that identical twins develop from a single egg and sperm; they have the same genetic make-up. Fraternal twins develop from the different eggs and sperms and are more like brothers and sisters).
- 1. Mendel’s selection of garden peas for his experiments must be emphasized. The varieties he chose had many clear-cut traits; for example, red versus white flowers, green versus yellow seed pods, etc. The students can then write essays on why Mendel chose plants rather than animals for his experiments.
- 2. Pea seeds bred for dominant and recessive factors can be obtained from a biological supply house. Students can grow their plants and simulate Mendel’s experiments in class.
- 1. What terms do scientists use for the heredity factors that determine the traits of an organism?
- 2. Why were there no short plants in the first generation?
- 3. Mendel found that there were tow heredity factors for each trait in pea plants. Give a few examples.
- 4. In mendel’s experiments when he crossed tall and short pea plants, what resulted in the first generation of plants?
- 5. How did Mendel decide which traits were dominant?
The Chart A below is an example of Punnett Square for an organism. The paired genes for a trait may be identical as with TT or tt. If both genes are same, the organism is homozygous, or pure for that trait.
The results of pollinating an egg of a homozygous tall pea plant is shown in the Punnett Square A. Everyone of the resulting pea plants will be heterozygous tall. In a similar process, other forms of crossing can be followed or calculated. (ex. crossing Tt x Tt or TT x Tt or Tt x tt).
These charts or Punnett Squares can also be used to show the probability of each resulting phenotype. For example, in the following chart B, the probability of producing tall plants from a cross between heterozygous tall pea plants are three out of four. (3:4) This means there is one chance in four of producing a short plant from such a cross.
- 1. Explain that the factors studied by mendel are now called genes, located in chromosomes in the nuclei of cells.
- 2. Explain with the aid of diagrams that the chromosomes are made up of long coiled, chemical chains known as DNA.
- 3. Demonstrate and describe the fact that during meiosis and mitosis, DNA is duplicated to make it possible for chromosomes and their genes to be passed on to new body cells and reproductive cells.
- 4. Define and explain with examples the terms genotype and phenotype, homozygous and heterozygous and variations in inheritance.
- 5. Explain the sex chromosomes (xx for females and xy for males) that determine the sex of the offspring.
Modeling Chromosomes
For many of the average students, modeling of chromosomes is necessary to understand the difference between mitosis and meiosis because they lack the facility to understand abstract concepts. Hence, they will find the models very helpful.
Each student is given some clay of various colors, with enough of each color to make pairs of “chromosomes”. The students can then draw circles on sheet of paper, to represent stages of the cells. The students then place the right number and kind of chromosomes in each kind of cell as it undergoes mitosis and as it undergoes tow divisions in meiosis. It is hoped that this will help clarify the difference between the two processes. This activity can be combined with exhibition of movies or video tapes describing DNA.
- 1. In what part of a cell are DNA, chromosomes and genes found?
- 2. List the parts of the DNA and describe how they are arranged.
- 3. Explain in your own words why DNA replication is necessary for meiosis and mitosis to occur.
- 1. Explain that double helix DNA model provides an adequate explanations of the duplication, mutation and transmission of genetic material.
- 2. Describe what scientists have learned from mapping genes.
- 3. Explain what is meant by homozygous genotype.
- 4. State how many genotypes and phenotypes are possible when tow heterozygous individuals mate.
- 5. Explain with diagrams how to use the Punnett Squares.
- 1. Students can construct models of the Double Helix DNA as conceived by Watson and Crick. Using colored construction paper. (As an alternative, students can draw diagrams of DNA as shown in prior studies, drawings or models). (See Appendix 4; p. 18, 18a, 18b)
- 2. Students can also use tongue depressors and strips of stiff plastic to form a double helix and to show the arrangement of the bases.
- 3. Slides, films and video tapes can be shown.
- 4. Some human genetics problems can be given to students to solve. For example, blond hair in humans is recessive to darker hair;, right-handedness is dominant to left handedness, etc.
- 5. Students can be instructed to make a family inventory of traits that have been passed from grandparents to students.
- 1. What do you think the scientists have learned from mapping genes?
- 2. What can you tell about the differences in genes of a boy having dark hair and a girl who is light-haired?
- 3. How are their genes similar?
- 4. What genotypes are produced from a heterozygous cross?
- 5 Knowing the phenotype of a flower what can you determine about its genotype?
- 1. State on example of incomplete dominance.
- 2. Name three factors that may cause genes to mutate.
- 3. Explain why plant breeders sometimes try to breed polyploid plants.
- 1. Students can be instructed to make a list of breeding examples in which breeders have taken advantage of incomplete dominance of traits to produce variations. (ex. cats, roses, cattle, breeding dogs, race horses, etc.).
- 2. Students can be asked to research and prepare reports on diseases like sickle-cell anemia, cystic fibrosis, diabetes and tay sacks disease.
- 1. What is an incomplete dominance? Give an example.
- 2. The colors of flowers in a flower garden are varied. What might you assume in the genotype of each of the differently colored flowers?
- 1. Describe when the sex of a child is genetically determined.
- 2. Name which gamete, male or female determines the sex of a child.
- 3. Give an example of a sex-linked characteristic in people.
- 4. Explain Down’s Syndrome, mutations, polyploidy.
- 1. Sex linked traits have long been studied in the common fruitfly-Drosophila. Traits for red/white eye color, normal/small wings and others can be studied by obtaining cultures of this fly from biological supply houses.
- 2. Red-green color blindness can be studied in class.
(N.B. Activities can be supplemented with AU-4)
- 1. When is the sex of a child determined?
- 2. Which gamete, male or female, determines a child’s sex?
- 3. What is an example o a sex-linked characteristics in people?
Also show charts of color blindness.
The Marfan syndrome affects some 20,000 persons in this country, including males and females of any race of ethnic group. The March of Dimes supports research on this and related disorders, and cooperates with other concerned organizations to keep the public informed.
Heart and blood vessels nearly always are affected. Heart valves—pairs or trios of flaps that keep the blood flowing in one direction through the heart— usually are oversized and floppy. Their action during heart-beats may allow brief reverse blood flow and cause a heart murmur (an abnormal sound heard through a stethoscope). The body’s largest artery, the aorta, is nearly always affected to some extent by the Marfan syndrome. Sl blood pumped from the heart passes forcefully into the aorta, which branches out to carry oxygen-rich blood to the entire body. A defective aorta can split in places and allow blood to leak into the chest or abdomen.
In some 50% of persons with the Marfan syndrome the lens of an eye is off-center. Nearsightedness is another common symptom, whether the lens is in place or not. The light-sensing inner lining of the eye (retina) may become detached. Persons with the Marfan syndrome are more prone than others to sudden lung collapse,
Figure 1 VISIBLE SYMPTOMS OF MARFAN SYNDROME
The gene is usually inherited from on parent. It is a “dominant” gene, which means that each child of a parent with the gene has a 50-50 chance of inheriting it. In about 15 percent of cases, a genetic accident (new mutation) occurs in a sperm of egg cell of an unaffected parent and so in passed on to an offspring.
A person who has such a gene and doesn’t know it may overdo physical activity which might harm vital body structures that are made up largely of connective tissue.
Because of heart value abnormalities, most Marfan syndrome patients are prone to infections in those valves. They must be treated with preventive antibiotics before any kind of surgery, including tooth-pulling, to keep bacteria out of the blood stream.
An artificial heart valve, can be implanted surgically to replace a weakended valve. Afterward, the patient is given anticlotting medication on a lifelong basis, because blood tends to clot in contact with artificial valves.
Although little can be done about the outward appearance of a person with classic Marfan syndrome, physical therapy, a brace, or surgery can often correct spinal curvatures that may arise. Crowded teeth can be adjusted by an orthodontist. Early and regular eye examinations may lessen eye problems common to these patients. Detached retinas can be restored by “bloodless surgery” with lasers. A hormone specialists may help with control of spinal curves and overall growth. Psychological attention may be necessary.
Figure 2
Heredity appears to play a role in about 25 percent of cases. In other 75 percent there is no family history of the defect, even among distant relatives. It is known that if both parents are normal and have a child with a cleft,the chances that subsequent babies will have a cleft increase progressively. If either parent has a cleft, there’s a four percent chance that their first baby will have a cleft, and the chances increase with each time they have an affected child.
Figure 3
Defective speech is one of the most serious results of cleft palate and, to a lesser extent, cleft lip. Psychological problems may result from speech difficulties and the child’s unusual appearance before clefts are repaired,a nd require a professional counselor’s help. Clefts have no relation to mental ability or retardation.
Ear infections are common. Difficulty in swallowing affects air pressure around the inner ear, spreading infection directly through the nose to ear. Frequent or severe ear infections may lead to hearing loss.
Many adults with Down syndrome age faster than their normal age group. Life expectancy among Down syndrome adults is about 50 years of age, but this varies widely.
Figure 4
In (B) DNA, on the opposite side, the base pairs sit astride the helix axis and are perpendicular to it.
This activity is ideal for Capsule Lesson 3.
- AV-1. Genes and Protein Synthesis.
- ____17Mins. 16mm. film.
- ____Hereditary diseases caused by aberrant hemaglobins, such as hemaglobin S, and especially sickle cell anemia. Also explains allelism and non-allelism.
- AV-2. Genetic Activity and Chromosome Chemistry. 29 Min. B&W. 16 mm.
- ____Reviews the contribution of Mendel, nucleic acids, chemical composition of chromosomes. Compares cell activity of DNA & RNA.
- AV-3. Genetic Chance 60min., color l6mm.
- ____Starts with problematical question: Suppose you were told that your unborn male child stood an even chance of being born with a crippling disease! You had the choice of terminating the pregnancy or allowing it to continue. Would you run the risk of aborting the healthy fetus or of bringing into the world a child crippled with a paralytic disease for the whole life.
- ____-very real chance of mothers who are carriers of hemophelia.
- ____-technique of diagnosing the sex of fetus.,
- AV-4. Genetic Defects: the broken code
- ____87 mins. color
- ____Features several revelations explaining the medical advances ocurring in the field of genetics; counseling to families having genetic problems, cystic fibrosis, Huntington’s Chorea,hemophilia, combined immune deficiency, Down’s Syndrome, sickle cell anemia, discussion of genetic screening finding potential parents, and ethical, moral and legal questions are raised.
- ____N.B. All the above can be located and loaned at Yale Audio Visual Center.
- AV-5. Basis of Birth Defects
- ____16mm about 5mins.
- ____Exposes the different types of birth defects of children.
- ____Above film available at March of Dimes.
- 1). Carolina Biological Supply Co., Burlington, North Carolina 27215.
- 2). Fisher Scientific Co., 1259 Wood St., Chicago, Il. 60622.
- 3). Wards’ Biology, Ward’s Natural Science Establishment Inc., 5100 West Henrietta Road, P.O. Box 92912, Rochester, N.Y. 14692-9012. 1-800-962-2660.
- 1). Contemporary/McGraw Hill Films, 1221 Avenue of the Americas, New York, N.Y. 10020.
- 2). Encyclopedia Britannica, Educational Corporation, 425 N.Michigan Ave., Chicago, Il 60611.
- 3). March of Dimes, 18 Elm Ave., Norwich, CT. 1-203-889-3883.
- 4). National Geographic Educational Society, Services, Dept. 79, Washington, D.C. 20036.
- 5). Yale Audio Visual Center, Educational Film Locator, 59 High St., New Haven. Tel. 1-203-432-2650.
2. Genetic Counselling, March of Dimes Birth Defects Foundation (1985)., New Haven County Chapter, New Haven, CT. 1-203-397-5008.
3. Huntington’s Disease , Huntington’s Chorea, (1976), National Institutes of Health, Bethesda, MD.20014.
4. March of Dimes Birth Defects Foundation, Public Health Education, Information Sheet, Genetic Series, 1275 Mamaroneck Ave., White Plains, N.Y. 10605.
5. Morholt, Brandwein & Joseph, A Source Book for the Biological Sciences (1966).
6. Otto, J.H.; Towle, A. & Bradley, J.V., (1981)., Modern Biology Holt, Rinehart & Winston Publishers, N.Y.
7. Tuberous Sclerosis, National Tuberous Sclerosis Association, Inc., (1984), P.O. Box 612, Winfield, Il. 60190. 1-312-668-0787.
Contents of 1987 Volume V | Directory of Volumes | Index | Yale-New Haven Teachers Institute
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