DNA – The Book of Life
Teachers’ Notes
1. Level
S4-S6
2. Duration
15 minutes
3. Learning Objectives
i) Recognise the structural and functional relationship between chromosomes, genes and nucleic acids.
ii) Recognise the molecular structure of DNA.
iii) Understand the nature of science through the discovery of the structure of DNA.
4. Curriculum Links
Biology (Secondary 4 - 6)Compulsory Part: II. Genetics and Evolution
Integrated Science (Secondary 4 – 6)
Compulsory Modules: C8 From Genes to Life – DNA as the genetic material
5. Contents of the Resource:
The programme of this resource introduces the structure and function of DNA as well as the discovery of its structure.
The first part of the programme introduces some interesting facts about DNA. The structural and functional relationships between cells, chromosomes and DNA are also discussed. The second part of the programme is about the structure of DNA. Some aspects of the nature of science will be explained with the story of how the structure of DNA was uncovered.
6. How to use this resource
The following suggestions are for teachers’ reference only and may be adjusted according to classroom situations.
i) This resource is divided into several segments in accordance with different contents. Teachers may use the corresponding segments for explaining concepts and consolidating student learning according to students’ pace of learning.
ii) Through classroom discussion and activity (DNA origami), students’ understanding of the molecular structure of DNA and the nature of science could be enhanced.
iii) After watching the programme, teachers may discuss the questions in Worksheet with students.
Teachers’ references:
i) DNA extraction:
http://cd1.edb.hkedcity.net/cd/science/biology/resources/L&t2/practical/Practical-30.pdf
ii) Classroom activity: DNA origami:
https://www.yourgenome.org/activities/origami-dna
Source: Genome Research Limited
iii) Reading to Learn: The 2% difference of DNA between human and chimpanzee
The 2% Difference:
http://discovermagazine.com/2006/apr/chimp-genome
Source: discovermagazine.com
Worksheet
After watching the programme, teachers may discuss the following questions with students.
1. In a human body cell, there are 46 chromosomes. These chromosomes come in pairs and we call them homologous chromosomes. In each pair of homologous chromosomes, one was inherited from the father and one from the mother.
Every cell in human body originates from the zygote and they should have the same genetic content. Then why cells in human body have different appearance and functions? (For example, why only pancreas cells, but not other cells, can secrete insulin?).
2. The 23rd pair of chromosomes in human cells determines the sex of the foetus. Amniocentesis is a medical procedure used inprenatal diagnosis, in which a small amount ofamniotic fluid is sampled from the amniotic sac surrounding a developing foetus.
a) According to your knowledge about cells and chromosomes, explain why this prenatal diagnosis could be used for determining the sex of the foetus.
b) Conduct an Internet search and give other examples of congenital diseases that could be diagnosed by amniocentesis.
3. Genes are small segments of DNA that form the basic units of genetic heredity. The base sequence on the DNA gives special instructions that are meaningful to the cells and control the various cellular activities of the organism.
a) What are genetically modified organisms (GMOs) and genetically modified (GM) foods? Give some examples of GM foods. How would GM foods affect agriculture and food manufacturing industry?
b) Gene mutation is the change in the base sequence of the DNA in a gene. The base sequence can be changed by a deletion, an insertion or duplication of base(s) in the DNA. Gene mutation causes changes in the structure and function of the protein produced. These non-functional proteins make cells cannot function properly.
Sickle-cell anaemia is a disease caused by gene mutation. People suffered from Sickle-cell anaemia produce abnormal haemoglobin and sickle-shaped red blood cells. These sickled-shaped cells can block blood vessels and may lead to organ damage.
The following diagram illustrates a segment of DNA found in normal haemoglobin producing gene and sickle-cell anaemia gene:
i) According to the diagram, what is the difference between normal haemoglobin producing gene and Sickle-cell anaemia gene?
ii) Explain why gene mutation can cause great changes in cellular functions. What are the advantages and disadvantages of gene mutation?
4.
According to the programme, human and chimpanzees have got only 2% DNA differences.
a) What do you think are the greatest difference between humans and chimpanzees?
b) Read the following article and find out why only 2% differences in DNA could cause such great differences in appearance, intelligence and behavior between human and chimpanzees.
The 2% Difference:
http://discovermagazine.com/2006/apr/chimp-genome
Source: discovermagazine.com
Worksheet (Suggested answers)
1. Every cell in human body have the same genetic content. Each cell has a copy of all the genes in an organism. However, some genes are expressed in certain types of cells only. The genes that are ‘switched on’ in each type of cell are different, causing differences in appearance and functions of different cells. In the case of insulin, the insulin is ‘switched on’ in some of the cells in pancreas, but ‘switched off’ in all other cells.
2. a) In amniocentesis, small amount of amniotic fluid which contains the foetal cells are extracted. The foetal cells are allowed to grow in a culture medium and the chromosomes inside are then examined under microscope. If both of the 23rd pair of chromosomes are X, then the foetus will be a female. If one is X and the other is Y, then the foetus will be a male.
c) Amniocentesis can also be used in the diagnosis of other diseases with abnormal number of chromosomes. For examples, trisomy 21 for Down syndrome, monosomy X sex chromosome for Turner syndrome and trisomy 18 for Edward syndrome.
3. a) Genetically modified organisms (GMOs) can be defined as organisms (i.e. plants, animals or microorganisms) in which the genetic material (DNA) has been altered in a way that does not occur naturally by mating and/or natural recombination. The technology is often called “modern biotechnology” or “gene technology”, sometimes also “recombinant DNA technology” or “genetic engineering”. It allows selected individual genes to be transferred from one organism into another, also between non-related species. Foods produced from or using GM organisms are often referred to as GM foods. Commonly known GM crops include soy, corn and cotton. GM foods are developed – and marketed – because there is some perceived advantage either to the producer or consumer of these foods. This is meant to translate into a product with a lower price, greater benefit (in terms of durability or nutritional value) or both.
b) i) The base T on the normal haemoglobin gene is replaced by the base A in the sickle-cell anaemia gene.
ii) A gene mutation is a permanent alteration in the DNA sequence that makes up a gene, such that the sequence differs from what is found in most people.
Gene mutation usually causes the production of mal-functioning protein that affect cellular activities and lead to genetic disorder.
Mutations can sometimes be beneficial. They provide a source of variations in a population and may give rise to new characters that are favourable to a certain environment. Variations are essential for natural selection to work and bring about evolution.
4. a) The biggest difference between humans and chimpanzees is intelligence. Human brain can perform a series of complex cognitive activities such as thinking, memory, reasoning and making decisions. The intelligence of chimpanzees is relatively lower. The main difference between chimpanzees and humans arise from how the brains are used.
b) Please refer to the article.
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