DNA and Heredity

Teachers’ Notes1. Level

S1-S3

2. Duration20 minutes

3. Learning Objectivesi) Recognise that the chromosomes found in the nucleus of each cell contain the

genetic material, DNA

ii) Recognise that there are 46 chromosomes in a human body cell, the 23rd pair is responsible for sex determination

iii)Recognise that a sperm and an ovum each carry one set of chromosomes (23 chromosomes) in humans, the zygote formed from fertilisation carries two sets of chromosomes (46 chromosomes)

iv) Recognise that DNA encodes the instructions that determine our different traits

v) Recognise that heredity is the passing of traits from one generation to the next as a result of the transmission of genetic information

vi) State that the double helix structure of DNA is based on the base pairing of A with T and C with G. The instructions encoded in DNA depend on the sequence of bases on the DNA

4. Curriculum Links

Science (Secondary 1 - 3) (2017)Unit 4 Cells, Human Reproduction and Heredity

5. Contents of the Resource:

This resource covers the two main themes “What is DNA?” and “What is Heredity?” It first gives an introduction about DNA. What is DNA and how DNA controls cellular activities and determines human traits are explained. Then, the structure of DNA, and

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how the instructions encoded in DNA are determined by the base sequences on the DNA are discussed. Lastly, the concept of heredity is explained with the shape of little finger as an example to illustrate the how traits are passed on from one generation to the next.

6. How to use this resourceThe 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 to explain important concepts to students. Teachers can also discuss with students the relationship between DNA and chromosomes, the importance of having only one set of chromosomes in sex cells, how base sequences on DNA acts as instructions to cellular activities, and how traits are passed on from one generation to the next in a family.

ii) Supplementary information like DNA origami, experiment manual for DNA extraction, worksheet for “Your name and DNA” and reading materials related to the content of this resource are also provided for teachers’ and students’ reference.

iii) Teachers may also complete the worksheet with students for consolidation.

Teachers’ references:

1. Know more about genetic diseasehttp://www.dh.gov.hk/english/main/main_cgs/files/Know_more_genetic_diseases_en.pdf

2. Gluocse-6-phosphate dehydrogenase (G6PD) deficiency http://www.dh.gov.hk/english/main/main_cgs/files/DH2289E%20G6PD%20English.pdf

3. Human female karyotype: https://www.dnalc.org/view/16243-Gallery-8-Human-female-karyotype.html

4. Human male karyotype: https://commons.wikimedia.org/wiki/File:NHGRI_human_male_karyotype.png

Courtesy: National Human Genome Research Institutehttps://www.genome.gov/

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Worksheet

I. Creating your family’s Tree of Trait

Select a human trait. In the space provided, draw a “Tree of Trait” to illustrate how this trait is passed on from one generation to the next in your family.

The trait you choose: ______________________________

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Remarks:

1. Your Tree of Trait should include three generations:

- The first generation: grandfather and grandmother - The second generation: Your father/mother and their brother(s) and sister(s). (You

only need to include your father’s OR mother’s brother(s) and sister(s) in the diagram.)

- The third generation: You and your brother(s), sister(s) and cousins

2. The following diagram is an example:

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II. Do you know that these characters are hereditary?

The following table list a series of human traits. Follow your teacher’s instruction and count the number of students in your class who have these traits.

Traits Eye lid Double eye lid

Source:

https://www.flickr.com/photos/53516453@

N05/albums/72157625425533057)

Single eye lid

Source:

https://www.flickr.com/photos/53516453@N05/

albums/72157625425533057)

Number of studentsShape of earlobe

Free earlobes

(Source: library.thinkquest.org)

Attached ear lobes

(Source: library.thinkquest.org)

Number of studentsDimples With dimples

(Source: https://pixabay.com)

With no dimples

Number of students

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Tongue rolling

Can roll tongue Cannot roll tongue

Number of studentsFreckles With freckles

(Source: https://pixabay.com)

With no freckles

Number of studentsShape of hairline

Straight hairline V-shape hairline

(Source: Kdhondt)

Number of studentsBlood Group

Group A Group B Group O Group AB

Number of studentsThumb bending

Thumb can bend back Thumb cannot bend back

Number of students

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Hair texture

Straight hair Curly hair

Number of students

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III. Information search

Some genetic diseases are listed below. Select one disease from the list and search for information about this disease. Prepare a PowerPoint presentation with no more than 10 slides, each slide with no more than 100 words and present your findings about the disease to your classmates.

1. Down syndrome

2. Cystic Fibrosis (囊性纖維變性)

3. Haemophilia (血友病)

4. Red-Green Colour Blindness

5. Glucose-6-Phosphate Dehydrogenase (G6PD) Deficiency

6. Albinism (白化病)

7. Huntington’s disease (亨丁頓舞蹈症)8. Spinal Muscular Atrophy (脊髓肌肉萎縮症)

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IV. DNA Extraction Experiment

Materials and apparatus: Strawberries (Kiwifruit or Onion can also be used) Gentle liquid detergent Ice-cold 95% ethanol Sodium chloride Gauze/coffee filter Plastic zipper bag 100 ml beaker Boiling tube and test tube rack 10 ml measuring cylinder Glass rod

Procedures:1. Prepare the extraction solution: Mix 5 ml of gentle liquid detergent with 1 g of sodium

chloride, add distilled water and dilute the solution to 50 ml.2. Chill the extraction solution in an ice-bath.

3. Cut the strawberries into small pieces.

4. Put the strawberries into a plastic zipper bag. Squeeze air out of the bag and seal the bag.

5. Gently mash the strawberries in the plastic zipper bag for about 3 minutes.

6. Add 10 ml of the extraction solution into the zipper bag. Mix the solution with the mashed strawberries. Use fingers and hands to further mash the strawberries inside the bag. (Avoid formation of bubbles inside the bag.)

7. Filter the fruit mixture through two layers of gauze over a beaker.

8. Using a measuring cylinder, transfer about 4 ml of the strawberry filtrate into a boiling

tube.

9. Tilt the boiling tube to 45o and pour well-chilled ethanol slowly into it.

10.Place the boiling tube on the rack and wait for 2-3 minutes. Observe the changes in the ethanol layer.

11.Use a wooden or glass rod to spool the whitish DNA fibres.

Remarks: The DNA extracted in this way contains impurities such as proteins that makes it visible to the naked eye. Pure DNA is virtually colourless.

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V. DNA and your name

1. Write your name in the spaces provided. (e.g. Annie Chan)

Example:A n n i e C h a n

2. Use the following English letter-DNA encoder, translate your name into DNA base sequence.

English letter-DNA encoder: Three Bases

English letters

Three Bases

English letters

Three Bases

English letters

Three Bases

English letters

AAA a CAA q GAA G TAA WAAC b CAC r GAC H TAC XAAG c CAG s GAG I TAG YAAT d CAT t GAT J TAT ZACA e CCA u GCA K TCA 1ACC f CCC v GCC L TCC 2ACG g CCG w GCG M TCG 3ACT h CCT x GCT N TCT 4AGA i CGA y GGA O TGA 5AGC j CGC z GGC P TGC 6AGG k CGG A GGG Q TGG 7AGT l CGT B GGT R TGT 8ATA m CTA C GTA S TTA 9ATC n CTC D GTC T TTC 0ATG o CTG E GTG U TTG SpaceATT p CTT F GTT V TTT .

Your Name:

The corresponding DNA base sequence:

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Example:

Your Name: A n n i e C h a n

The corresponding DNA base sequence: CGG AT

CATC AGA ACA CTA ACT AAA ATC

VI. DNA origami:

The DNA origami activity allows students to create their own paper model of DNA double helix and learn about complementary base pairing in DNA molecule.

https://www.yourgenome.org/activities/origami-dna

(Source：Genome Research Limited)

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VII. Multiple Choice Questions

(Please choose the best answer.)

1. The following diagram shows the chromosomes found in the body cell of a young person:

(Source: http://www.asean-endocrinejournal.org/index.php/JAFES/article/view/307/759)

Which of the following description about the young person is correct?

A. The person is a normal male.B. The person is a normal female.C. The person is a male with Down syndrome.D. The person is a female with Down syndrome.

2. Which of the following human body cells possess 46 chromosomes?

(1)Nerve cell(2)Muscle cell(3)Sperm(4)Fertilized egg (Zygote)

A. (1) onlyB. (1) and (2) onlyC. (2), (3) and (4) onlyD. (1), (2) and (4) only

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3. Which of the following statements about DNA are correct?

(1)The full name of DNA is ribonucleic acid.(2)DNA is the genetic material that pass from one generation to the next.(3)DNA can control cellular activities.

A. (1) and (2) onlyB. (2) and (3) onlyC. (1) and (3) onlyD. (1), (2) and (3)

4. Which of the following statements about chromosome are correct?

(1)DNA could be found in chromosomes(2)All organisms have the same number of chromosomes(3)The 23rd pair of chromosomes in human body cells are responsible for sex

determination

A. (1) and (2) onlyB. (2) and (3) onlyC. (1) and (3) onlyD. (1), (2) and (3)

5. Doctors may withdraw amniotic fluid from the uterus of pregnant women for examination. The purpose is to:

A. examine the content of amniotic fluidB. examine the chromosomes in amniotic fluidC. withdraw mother cells in the amniotic fluid for examinationD. withdraw foetus cells in the amniotic fluid for examination

6. Which of the following statement about human sperms, eggs and fertilized eggs is incorrect?

A. Sperms contain 23 pairs of chromosomes.B. Eggs contain 23 chromosomes.C. Fertilized eggs contain 23 pairs of chromosomes.D. A fertilized egg contains the genetic material of father and mother.

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7. Which of the following base cannot be found in DNA?

A. GB. UC. TD. C

8. If the base sequence on one chain of the DNA double helix is CCTTAGA, the base sequence on the other chain will be

A. GAATCTAB. GGAATCTC. CCAAAGAD. CCTTAGA

9. The specific base sequence on DNA will become a ____________ and control cellular activities.

A. chromosomesB. geneC. meaningful message to the cellD. sentence

10.Trait refers to

A. the sex of an organismB. the sex organ of an organism C. the characters related to sexD. genetically determined characteristics

11.The father of a family is red-green colour-blindness. His son has normal vision. The reason is

A. The father is not the biological father of the son.B. Father passes half of his genetic material to his children. He did not pass the colour-

blindness genetic material to his son.C. Colour-blindness is not a genetic disease.D. The nutrient-rich diet of the son cured his colour-blindness.

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12.Which of the following can explain why siblings do not carry identical traits?

A. Siblings may have different sexes.B. Father and mother pass different genetic material to different children.C. The situations when mother give birth to different children are not the same.D. Father and mother pass different number of chromosomes to different children.

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Worksheet (Suggested answers)

VIII. Multiple Choice questions

1. B2. D3. B4. C5. D6. A7. B8. B9. C10. D11. B12. B

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