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GENETICS: Chromosomes, cells and genes

Prof.ssa Elena TibaldiAS 2012-2013

CLIL MODULE - BIOLOGY

2° Liceo Scientifico

Istituto Sant’Anna

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Contentobjectives

To know:• concept of chromosome, gene and allele• concept of homozygous and heterozygous

To be able to:• predict the genotype and phenotype of the offspring using Punnettsquare

To be aware of:• the effect of genetic mutations in the onset of genetic disorders• the effect of non-disjunction during meiosis

Languageobjectives

Expand knowledge of content-specific vocabularyWorking on scientific words: use of prefixes and suffixes to conveyprecise meaningDescribe a process/an experiment and motivate resultsPassive forms of the verbsLink words and sequencers

Prerequisites The structure of DNA see review slideCell cycle and division; mitosis and meiosis see review slides

Task-basedactivity

Groupwork: powerpoint presentation

Timing Second term; II yearClasses: IIA and IIB Liceo

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HUMAN TRAITS AND GENETIC INHERITANCEBrainstorming compare inherited human traits

Dark/blond hair

Curly/straight hair

Dark/light-coloured skin

Otherhumangenetictraits

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Eye and hair colours are called ...................................

Parents pass on traits to their offspring in their .............................

Different ........................ control different traits.

Genes are found on .................................................., that are in the

............................... of the cell.

DNA provide information on how to build each part of your.............................

DNA has the shape of a double.......................................

Activity 1 see English textbook pag 314

Activty 2 see English textbook pag 314

Activity 3 Complete the following passage using the words listed below:

DNA – genes - nucleus - instructions – body – chromosomes – traits -helix

ACTIVITIES ON CONTENT-SPECIFIC VOCABULARY

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REVIEW THE STRUCTURE OF DNA

DNA is a double helical structure consisting of twofilaments (strands) made of nucleotides.

The two strands are complementary in nucleotidicsequence (A-T) and (C-G) and are kept together byhydrogen bonds between the complementary bases of the two strands. Hydrogen

bonds

6http://www.funsci.com/fun3_en/dna/dnaen.htm

LAB ACTIVITY: DNA EXTRACTION FROM FRUITMaterials:• 100g of fruit pulp (½ banana /3 kiwis / ½ pear /some strawberries)• salt• liquid detergent (not from concentrate)• Pineapple juice• Plastic pipettes• 5ml syringes• plastic dishes, forks, knives and spoons• Beakers and cylinders•Test tubes• 95% ice-cold alcoholExperimental procedure:1. Peel the fruit and place it in a plastic dish2. Using knife and fork, mash the fruitpulp for several minutes3. In a 250 ml beaker prepare the extraction solution by adding:

3g (½ tablespoon) of salt90 ml distilled water10 ml liquid detergent

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4. Add the mashed pulp into the extraction solution and stir for 10 minutes without making bubbles.

5. Filter the solution through a paper filter into a 100ml beaker. Make sure the top part of the filter is foldedover the top of the beaker and that the bottom of the filter does not touch the bottom of the cup

6. Put 5ml of the filtrate into a test tube.

7. Add 1ml of pineapple juice. Mix 2-3 minutes.

8. Slowly add 6ml of ice-cold alcohol.

9. Wait a few minutes until you see the DNA comingout of solution as a cotton thread in the tube.

10. Collect the DNA with a toothpick

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http://www.funsci.com/fun3_en/dna/dnaen.htm

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AT THE END OF THE LAB ACTIVITY, ANSWER THE FOLLOWING QUESTIONS

1. What is the purpose of mashing up the fruit pulp?................................................2. What does the extraction solution do?...................................................................3. What is the purpose of the detergent in the extraction solution?

To destroy cell membraneTo digest fruit fibersTo make DNA precipitation

4. Why do we filter the solution?...............................................................................5. What is the purpose of adding the pineapple juice?..............................................6. What happens when you add the alcohol to the filtrate?.....................................7. What does the DNA look like?...............................................................................8. Why are bubbles formed during ethanol precipitation?

Bromeline contained in the pineapple juiceLow temperature of ethanolPresence of detergent

9. Place the following steps of the experimental procedure in the correctorder

digestion of proteinsethanol precipitationbreak down of cell membranes

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DNA ORGANIZATION IN CHROMOSOMES

DNA is wrapped around proteins calledHYSTONES and condensed to formCHROMOSOMES

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The prefix CHROM- is referred to colourExercise find out the meaning of the following terms:• Chromatin: ........................................................................

• Sister chromatids: ..........................................................

WORD STUDY: THE CHROMOSOME

CHROMOSOME = stained (=coloured) body

• Nucleosome: ..........................................................................................................................................

• Lysosome: ..............................................................................................................................................

• Centrosome: ............................................................................................................................................

• Somatic cell: ........................................................................................................................................

The prefix or suffix -SOME is referred to body.Exercise find out the meaning of the following terms:

Walther Flemming (1843-1905), a German biologistand founder of cytogenetics, was the first scientistthat stained the chromatin in the nucleus using aniline dye. He correlated the chromatin with the thread-like structures that were lately named chromosomes. Other dyes for nuclear staining are commonly used in the lab: Giemsa, methylene blue and acridine orange.

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..........................................................discovered the chromosomes and the process of mitosis.

Walter Flemming

.......................................................... identified laws of inheritanceworking with pea plants.

GUESS WHO ...?

..........................................................discovered the structure of DNA.

James Watson and Francis Crick

Gregor Mendel

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REVIEW THE CELL CYCLE

Animation on cell cycle:http://www.cellsalive.com/cell_cycle.htm

THE PROCESS OF CELL DIVISIONAll living organisms need to produce new cells (daughter cells). They can only do this bydivision of pre-existing cells (parent cells).

In eukaryotic cells mitosis• division of the nucleus to form twogenetically identical nuclei• it occurs during growth, embryonicdevelopment, tissue repair (ie woundhealing), tissue regeneration (ie. starfish) and asexual reproduction

In prokaryotic cells binary scission• replication of single circular chromosome• two copies of the chromosome move to the cell poles• Division of the cytoplasm to form twodaughter cells• it occurs in asexual reproduction

The life of the cells is an ordered sequence of events called cell cycle. The cell cycle is divided in two parts:• interphase It is the longest phase of the cycle, a very active period between two subsequentdivisions; it consists of three phases: G1, S and G2. • cell division mitosis or meiosis

Cell cycle is tightly regulated by a complex system of proteins named cyclins and kinases.

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ACTIVITY 1- PAIRWORK Name and number the phases of mitosis

Phase N°......:..............................

Phase N°......:..............................

Phase N°......:..............................

Phase N°......:..............................

ACTIVITY 2- INDIVIDUALLY AT HOME http://www.cellsalive.com/puzzles/mitosis/index.html

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WORKING ON LANGUAGE: The expressions of time

Exercise 1: complete the sentences choosing the correct expression of time amongthose listed below. Some expressions can be used more than once, others are not usedat all.

1) Crossing-over occurs........................................................ the prophase I of meiosis I.

2)................................................................ of the mitosis, two genetically identical daughtercells have been formed.

3) .............................................. of interphase, the cell begins mitosis.

4) .............................................. the S phase, DNA molecule is replicated.

Finally, during, first, subsequently, then, at the end, after, afterwards, at the beginning

Exercise 2: Write a short passage on your notebook, describing the sequence of eventsoccurring during mitosis, using at least 5 different expressions of time.

GRAMMAR REVIEW: Expressions of time are very useful whendescribing the order in which the events occur over time.

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MEIOSIS IS THE CELL DIVISION OCCURRING IN SEXUAL REPRODUCTION

Sexual reproduction is a way of producing offspring that also generates genetic diversityin a species. In eukaryotic organisms, it involves the process of fertilization.

In the process of fertilization, male gamete (sperm cell) penetrates the female gamete (egg cell) to produce a zygote (fertilized egg) which will then develop into a new organism.

Gametes are produced in the gonads through a process of cell division called meiosis. Meiosis consists of two subsequent cell divisions, preceeded by only one DNA replication.

During the prophase I, an exchange of genetic material (crossing-over) between homologous chromosomesoccurs.

In Meiosis I, homologous chromosomes separate into the two haploid daughter cells; in Meiosis II (similar tomitosis, the sister chromatides separate into the fourhaploid daughter cells.

The final result is the production of four daughter cells(gametes) each of which possesses half of the chromosome number (haploid cells) and is geneticallydifferent from the parent cell.

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GLOSSARY CONTENT-SPECIFIC VOCABULARY

TERM(translation)

DEFINITION

Heredity / Inheritance( )

Genetic information is passed on from parents to their offspring

Chromosome( )

Thread-like structure made up of DNA and proteins

Gene ( )

Sequence of DNA coding for a protein

Gamete ( )

Male cell (sperm) or female cell (egg) are produced in the gonadsand join together to form a new organism (zygote)

Allele( )

One of two or more possible forms of a gene which are found on a chromosome. It can be dominant (A) or recessive (a)

Genotype( )

The genotype is the actual genetic make up of an individual and derives form the combination of alleles of the genes from bothparents.

Phenotype( )

The phenotype is what that individual looks like. The phenotypeis the visible expression of genes.

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TERM(translation)

DEFINITION

Carrier( )

an individual that has a recessive allele of a gene that does nothave an effect on his phenotype

Codominant alleles( )

pairs of alleles that both affect the phenotype when present in a heterozygote

Homozygous( )

Pair of identical alleles of a gene. It can be homozygousdominant (AA) or recessive (aa)

Heterozygous( )

Pair of different alleles of a gene (Aa)

To breed( )

Fertilize the organism to get offspring. Same meaning as “tocross”

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GENETICS – THE STUDY OF INHERITANCE

When living organisms reproduce, they pass on their features to the offspring.

The mechanism of inheritance wasdiscovered by Mendel who performedexperiments using varieties of pea plantsdiffering for specific traits.

Plants with different traits were crossedby tranferring the male pollen from one variety to the female pistil of anothervariety.

The offspring were collected and grown tofind out what their traits were.

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MENDEL – VARIETIES OF PEAS

Note that for each trait only twophenotypes are present; the phenotype in the left column is dominant, the otherrecessive.

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MENDEL’S CHARACTERS (2)

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MENDEL’S LAW OF INHERITANCE

When breeding a spherical(round) seed with a dented(wrinkled) seed, the first generation (F1) is representedby 100% spherical seeds. Thismeans that spherical trait isdominant and that dented trait is recessive.

After breeding two F1 spherical seeds, Mendelobserved, in the F2 generation, both sphericaland dented seeds in a 3:1 ratio.

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DOMINANT OR RECESSIVE?

A dominant allele controls a trait that appears whenever the dominant allele ispresent as homozygous dominant (AA) or as heterozygous (Aa). The dominantallele is indicated with the capital letter.

A recessive allele controls a trait that appears only when present in homozygous recessive organisms (aa); the recessive allele is indicated with a small letter.

Aa

Aa A= yellow seed (dominant)a= green seed (recessive)

This picture represents thePUNNETT SQUARE

Note that AA and Aa haveidentical phenotype.

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Male’s alleles are listed across the top of the square; female’s alleles are listed on the side.The genotype of the offspring is obtained by crossingparents’ alleles.

THE PUNNETT SQUAREThe Punnett square shows how the different combination of genes from male and femalegametes generates the genotype in the offspring.It helps predict which traits are likely to appear in the offspring.

Example:

If B is the allele for purple flowers and b is the allele for white flowers, the offspring are:

• BB homozygous dominant plantwith purple flowers;• Bb heterozygous plant with purpleflowers• bb homozygous recessive plant withwhite flowers

Note that both the homozygousdominant and the heterozygous havethe same phenotype.

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Complete the following

Punnett squares

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DIHYBRID CROSSINGWhen breeding two F1 seeds with two features (shape and colour) (RrYy genotype; smoothyellow phenotype), the phenotype of the offspring results in a fixed ratio:9 (smooth yellow) : 3 (smooth green) : 3 (wrinkled yellow) : 1 (wrinkled green)

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EXERCISE -PAIRWORKMatch the words with the correct definitions

1 2 3 4 5 6 7 8 9 10

1 inheritance2 chromosomes3 gametes4 haploid number5 diploid number6 alleles7 dominant8 genotype9 recessive10 phenotype

a) Number of chromosomes found in a gameteb) Different forms of a genec) Process by which genetic information is passed on from

parents to their offspringd) A characteristic that can be seene) Trait that can be seen only in homozygous recessive formf) The genes for a particular characteristicg) Thread-like structures made up of DNA and proteinsh) Number of chromosome found in a normal celli) Sex cells which only have half the usual number of

chromosomesj) Trait that can be seen both in homozygous and in heterozygous

organisms

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INCOMPLETE DOMINANCE

Incomplete dominance occurs when no trait dominates on the other; the heterozygousis different from the homozygous dominantbecause an intermediate trait shows up in the heterozygous organism.

Example: red snapdragon plant (RR) crossedwith a white snapdragon plant (rr) makesplants with pink flowers (Rr).

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CODOMINANCECodominance occurs when both alleles can be expressed or visible.In humans, there are four blood types (phenotypes): A, B, AB, and O. Blood type is controlled by three alleles: A, B, O. O is the recessive allele: two O alleles must be present for the person to have type O blood. A and B are codominant if a person receives A allele and B allele from parents, his bloodtype is AB.

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SEX CHROMOSOMES MALE OR FEMALE?

father

mother

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Non-disjunction during meiosis causes the altered number of chromosomes in the gamete.Here a few examples of chromosomal defects.

1) Defects in the number of sexual chromosomes: individuals can live normally, but are generally sterile.• Turner Syndrome (XO) female with only one X chromosome• Klinefelter Syndrome (XXY) male, with two X chromosomes

2) Defects in the number of autosomes: in the majority of cases, defects in the number of autosome causes abortion; the only possibility of survival is:• Edwards syndrome (trisomy of chr. 18) 90% of affected children die within the first six months because of heart damage and failure.

• Patau syndrome (trisomy of chr. 13) affected children die within the first threemonths because of damage to the nervous system and heart failure.

• Down Syndrome (trisomy of chr.21) affected children show mental retardation and delay in physical growth. Many children with Down syndrome are educated in regular schoolclasses while others require specialised educational facilities. Education and proper care has been shown to improve quality of life significantly. Many adults with Down Syndromeare able to work at paid employment in the community, while others require a more sheltered work environment. Life expectancy depends on the severity of the disease.

DEFECTS IN THE NUMBER OF CHROMOSOMES

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GENETIC DISORDERS

AUTOSOMAL DOMINANT =Mutation occurs in the dominant allele(A*) Both homozygous dominant(A*A*) and heterozygous (AA*) individuals are sickEx. Huntington’s disease

AUTOSOMAL RECESSIVE =Mutation occurs in the recessive allele (a*)

Homozygous recessive (a*a*) individualis sick; heterozygous (Aa*) is carrier.Ex. Albinism; sickle-cell anemia; cysticfibrosis; Tay-Sachs syndrome.

X-LINKED DOMINANT = Mutationoccurs in an allele on the X chromosome(X*):X*X* homozygous female, sickX*X heterozygous female, sickX*Y male, sickEx. Rett syndrome

X-LINKED RECESSIVE =Mutation occurs in an allele on the X chromosome (X*):X*X* homozygous female, sickX*X heterozygous female, carrierX*Y male, sickEx. Duchenne muscolar dystrophy; haemophilia; color blindness (daltonism)

Y-LINKED = Mutation occurs in an allele on the Y chromosome(Y*):XY healthy maleXY* sick male

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THE SICKLE-CELL ANEMIA

HbAHbS HbAHbS

HbAHbA HbAHbS HbSHbS

The heterozygous HbAHbS shows anadvantage in case of malaria: Plasmodiumfalciparum does not live in sickle cell, therefore heterozygous individuals are notaffected by malaria.

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ALBINISM NOT ONLY A HUMAN CONDITIONAlbinism (from Latin “Albus” = white) is caused by a genetic mutation of a gene coding foran enzyme involved in the production of melanin in skin, eyes and hair.

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COLOUR BLINDNESS (DALTONISM)

Colour blindness or colour vision deficiency is the inability or decreased ability to seecolours, or perceive colour differences, under normal lighting conditions.

The English chemist John Dalton published the first scientific paper on this subject in 1798, "Extraordinary facts relating to the vision of colours", after the realization of hisown colour blindness.Because of Dalton's work, the general condition has been called daltonism.

COLOUR BLINDNESS TEST

Vision is allowed by photoreceptors called cone cells (activein normal daylight) and rod cells (active in low light). Colour blindness is caused by mutations of genes involved in colour vision which are present on the X-chromosome.

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HAEMOPHILIA AND THE ENGLISH ROYAL FAMILY

Haemophilia is caused by a mutation in the gene codingfor the clotting factor VIII. Such mutation causesproblems during blood clotting after injures. Since this recessive gene is encoded in the X chromosome, males can be healthy or sick; females are carriers.

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WORKING ON LANGUAGE: The passive form of the verbs

GRAMMAR REVIEW: in many scientific reports, the use of the passive form of the verbsis very common.

Exercise below, a few sentences found in the previous slides are listed. Complete them and convert them from the passive to the active form.

1) Two strands of DNA are kept together by ....................... bonds.

......................................................................................................................................................................

2) Cell cycle is tightly regulated by a complex system of proteins named ...................... and ...................

......................................................................................................................................................................

3) The mechanism of ............................... was discovered by Mendel

......................................................................................................................................................................

4) The genotype of the offspring is obtained by ...............................parents’ alleles.

......................................................................................................................................................................

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5) Blood type is controlled by three alleles: ........, ..........., ...........

...................................................................................................................................................................

6) Albinism (from Latin “Albus” = .............................) is caused by a genetic mutation.

....................................................................................................................................................................

7) Color ............................ is caused by mutations of genes present on the X-chromosome.

....................................................................................................................................................................

8) Haemophilia is caused by a mutation in the gene coding for the ......................factorVIII

....................................................................................................................................................................

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ACTIVITY GENETICS AND FAMILY TREE

Observe the family tree and answer the questions:

1) Is there any female affected?2) Is there any male affected?3) Which is the type of genetic inheritance

shown in this family tree?Autosomic dominantAutosomic recessive X-linkedY-linked

Motivate your answer......................................................................................................................................................................................................................................................................

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Aim of the activity

Each group elaborates a powerpoint presentation in which the outstanding results on topics related to genetics are described and presented it to the whole class.

Procedure Students, in small groups, should choose one of the following topic and elaborate a powerpoint presentation on:

Recent discoveries on gene therapyRelation between genetics and cancerDescription of a genetic disorder

Students can find the above information by consulting sciencetextbooks, other books, internet.Bibliography and sitography must be included in the presentation.

Language skills Oral activity speaking in small groups / with whole classWritten activity powerpoint presentationUse of content-specific language

TASK-BASED ACTIVITY

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Books and textbooks:• Gateway to science – Thompson Heinle• Biology. Course companion – Allott and Mindorff- Oxford• Science. Oxford content and language support – Kauser and O’Donoghue - Oxford• Science – Keith Kelly – Macmillan Vocabulary Practice Series – Macmillan• Biology for IB diploma – standard and high level – Andrew Allott – Oxford• Edexcel IGCSE Biology – Bradfield and Potter- Pearson

Websiteshttp://www.bbc.co.uk/schools/gcsebitesize/science/http://www.cellsalive.com/cells/3dcell.htm http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa_pre_2011/cellshttp://www.bbc.co.uk/scotland/learning/bitesize/standard/biology/investigating_cells/cells_and_diffusion_rev2.shtml http://www.cellsalive.com/cell_cycle.htmhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__mitosis_and_cytokinesis.htmlhttp://www.cellsalive.com/mitosis.htmhttp://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa_pre_2011/celldivision/http://www.cellsalive.com/puzzles/mitosis/index.htmlhttp://science.education.nih.gov/supplements/nih1/cancer/activities/activity2_animations.htmhttps://wikispaces.psu.edu/display/bio110/Home

BIBLIOGRAPHY and SITOGRAPHY