Download Chromosome - Didattica Orizzonte Scuola

CLIL MODULE - BIOLOGY
2° Liceo Scientifico
Istituto Sant’Anna
GENETICS: Chromosomes, cells and genes
Prof.ssa Elena Tibaldi
AS 2012-2013
1
To know:
• concept of chromosome, gene and allele
• concept of homozygous and heterozygous
Content
objectives
To be able to:
• predict the genotype and phenotype of the offspring using Punnett
square
To be aware of:
• the effect of genetic mutations in the onset of genetic disorders
• the effect of non-disjunction during meiosis
Language
objectives
Expand knowledge of content-specific vocabulary
Working on scientific words: use of prefixes and suffixes to convey
precise meaning
Describe a process/an experiment and motivate results
Passive forms of the verbs
Link words and sequencers
Prerequisites
The structure of DNA Æ see review slide
Cell cycle and division; mitosis and meiosis Æ see review slides
Task-based
activity
Groupwork: powerpoint presentation
Timing
Second term; II year
Classes: IIA and IIB Liceo
2
HUMAN TRAITS AND GENETIC INHERITANCE
Brainstorming Æ compare inherited human traits
Other
human
genetic
traits
Dark/blond hair
Curly/straight hair
Dark/light-coloured skin
3
ACTIVITIES ON CONTENT-SPECIFIC VOCABULARY
Activity 1 Æ see English textbook pag 314
Activty 2 Æ see English textbook pag 314
Activity 3 Æ Complete the following passage using the words listed below:
DNA – genes - nucleus - instructions – body – chromosomes – traits helix
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.......................................
4
REVIEW Æ THE STRUCTURE OF DNA
DNA is a double helical structure consisting of two
filaments (strands) made of nucleotides.
The
two
strands
are
complementary in nucleotidic
sequence (A-T) and (C-G) and
are
kept
together
by
hydrogen bonds between the
complementary bases of the
two strands.
Hydrogen
bonds
5
LAB ACTIVITY: DNA EXTRACTION FROM FRUIT
Materials:
• 100g of fruit pulp (½ banana /3 kiwis / ½ pear /some strawberries)
• salt
• liquid detergent (not from concentrate)
1-2
• Pineapple juice
• Plastic pipettes
• 5ml syringes
• plastic dishes, forks, knives and spoons
• Beakers and cylinders
•Test tubes
• 95% ice-cold alcohol
Experimental procedure:
1. Peel the fruit and place it in a plastic
dish
2. Using knife and fork, mash the fruit
pulp for several minutes
3. In a 250 ml beaker prepare the
extraction solution by adding:
3g (½ tablespoon) of salt
90 ml distilled water
10 ml liquid detergent
3
6
http://www.funsci.com/fun3_en/dna/dnaen.htm
4. Add the mashed pulp into the extraction solution and
stir for 10 minutes without making bubbles.
4
5. Filter the solution through a paper filter into a 100ml
beaker. Make sure the top part of the filter is folded
over 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.
5
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 coming
out of solution as a cotton thread in the tube.
6-7
10. Collect the DNA with a toothpick
8
9-10
7
http://www.funsci.com/fun3_en/dna/dnaen.htm
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 membrane
‰ To digest fruit fibers
‰ To 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 juice
‰ Low temperature of ethanol
‰ Presence of detergent
9. Place the following steps of the experimental procedure in the correct
order
‰ digestion of proteins
‰ ethanol precipitation
‰ break down of cell membranes
8
DNA ORGANIZATION IN CHROMOSOMES
DNA is wrapped around proteins called
HYSTONES and condensed to form
CHROMOSOMES
9
WORD STUDY: THE CHROMOSOME
The prefix CHROM- is referred to colour
Exercise Æ find out the meaning of the following
terms:
• Chromatin: ........................................................................
• Sister chromatids: ..........................................................
The prefix or suffix SOME is referred to body.
Exercise Æ find out the
meaning of the following
terms:
• Nucleosome: ..........................................................................................................................................
• Lysosome: ..............................................................................................................................................
• Centrosome: ............................................................................................................................................
• Somatic cell: ........................................................................................................................................
CHROMOSOME =
stained (=coloured) body
Walther Flemming (1843-1905), a German biologist
and founder of cytogenetics, was the first scientist
that stained the chromatin in the nucleus using aniline
dye. He correlated the chromatin with the threadlike structures that were lately named chromosomes.
Other dyes for nuclear staining are commonly used in
10
the lab: Giemsa, methylene blue and acridine orange.
GUESS WHO ...?
..........................................................
discovered the chromosomes and
the process of mitosis.
Walter Flemming
..........................................................
discovered the structure of DNA.
Gregor Mendel
..........................................................
identified laws of inheritance
working with pea plants.
James Watson and Francis Crick
11
REVIEW Æ THE
CELL CYCLE
The life of the cells is an ordered sequence of
events called cell cycle.
The cell cycle is divided in two parts:
• interphase Æ It is the longest phase of the cycle,
a very active period between two subsequent
divisions; it consists of three phases: G1, S and G2.
• cell division Æ mitosis or meiosis
Cell cycle is tightly regulated by a complex system
of proteins named cyclins and kinases.
Animation on cell cycle:
http://www.cellsalive.com/cell_cycle.htm
THE PROCESS OF CELL DIVISION
All living organisms need to produce new cells (daughter cells). They can only do this by
division of pre-existing cells (parent cells).
In prokaryotic cells Æ binary scission
• replication of single circular chromosome
• two copies of the chromosome move to the
cell poles
• Division of the cytoplasm to form two
daughter cells
• it occurs in asexual reproduction
In eukaryotic cells Æ mitosis
• division of the nucleus to form two
genetically identical nuclei
• it occurs during growth, embryonic
development, tissue repair (ie wound
healing), tissue regeneration (ie. starfish)
12
and asexual reproduction
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
13
WORKING ON LANGUAGE:
The expressions of time
GRAMMAR REVIEW: Expressions of time are very useful when
describing the order in which the events occur over time.
Exercise 1: complete the sentences choosing the correct expression of time among
those listed below. Some expressions can be used more than once, others are not used
at all.
Finally, during, first, subsequently, then, at the end, after, afterwards,
at the beginning
1) Crossing-over occurs........................................................ the prophase I of meiosis I.
2)................................................................ of the mitosis, two genetically identical daughter
cells have been formed.
3) .............................................. of interphase, the cell begins mitosis.
4) .............................................. the S phase, DNA molecule is replicated.
Exercise 2: Write a short passage on your notebook, describing the sequence of events
14
occurring during mitosis, using at least 5 different expressions of time.
MEIOSIS IS THE CELL DIVISION
OCCURRING IN SEXUAL REPRODUCTION
Sexual reproduction is a way of producing offspring that also generates genetic diversity
in 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 chromosomes
occurs.
In Meiosis I, homologous chromosomes separate into the
two haploid daughter cells; in Meiosis II (similar to
mitosis, the sister chromatides separate into the four
haploid 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 genetically
different from the parent cell.
15
GLOSSARY Æ 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 gonads
and join together to form a new organism (zygote)
)
One of two or more possible forms of a gene which are found on
a chromosome. It can be dominant (A) or recessive (a)
Allele
(
Genotype
(
)
Phenotype
(
)
The genotype is the actual genetic make up of an individual and
derives form the combination of alleles of the genes from both
parents.
The phenotype is what that individual looks like. The phenotype
is the visible expression of genes.
16
TERM
(translation)
DEFINITION
Carrier
(
)
an individual that has a recessive allele of a gene that does not
have an effect on his phenotype
)
pairs of alleles that both affect the phenotype when present in
a heterozygote
)
Pair of identical alleles of a gene. It can be homozygous
dominant (AA) or recessive (aa)
Codominant alleles
(
Homozygous
(
Heterozygous
(
Pair of different alleles of a gene (Aa)
)
To breed
(
)
Fertilize the organism to get offspring. Same meaning as “to
cross”
17
GENETICS – THE STUDY OF INHERITANCE
When living organisms reproduce, they pass
on their features to the offspring.
The mechanism of inheritance was
discovered by Mendel who performed
experiments using varieties of pea plants
differing for specific traits.
Plants with different traits were crossed
by tranferring the male pollen from one
variety to the female pistil of another
variety.
The offspring were collected and grown to
find out what their traits were.
18
MENDEL – VARIETIES OF PEAS
Note that for each trait only two
phenotypes are present; the phenotype in
the left column is dominant, the other
recessive.
19
MENDEL’S CHARACTERS (2)
20
MENDEL’S LAW OF INHERITANCE
When breeding a spherical
(round) seed with a dented
(wrinkled) seed, the first
generation (F1) is represented
by 100% spherical seeds. This
means that spherical trait is
dominant and that dented trait
is recessive.
After breeding two F1
spherical seeds, Mendel
observed, in the F2
generation, both spherical
and dented seeds in a 3:1
ratio.
21
DOMINANT OR RECESSIVE?
A dominant allele controls a trait that appears whenever the dominant allele is
present as homozygous dominant (AA) or as heterozygous (Aa). The dominant
allele 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
A= yellow seed (dominant)
a= green seed (recessive)
Note that AA and Aa have
identical phenotype.
Aa
This picture represents the
PUNNETT SQUARE
22
THE PUNNETT SQUARE
The Punnett square shows how the different combination of genes from male and female
gametes generates the genotype in the offspring.
It helps predict which traits are likely to appear in the offspring.
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 crossing
parents’ alleles.
Example:
If B is the allele for purple flowers and
b is the allele for white flowers, the
offspring are:
• BB Æ homozygous dominant plant
with purple flowers;
• Bb Æ heterozygous plant with purple
flowers
• bb Æ homozygous recessive plant with
white flowers
Note that both the homozygous
dominant and the heterozygous have
the same phenotype.
23
24
http://www.exploringnature.org/db/detail.php?dbID=22&detID=2290
ACTIVITY:
Complete the
following
Punnett squares
DIHYBRID CROSSING
When breeding two F1 seeds with two features (shape and colour) (RrYy genotype; smooth
yellow phenotype), the phenotype of the offspring results in a fixed ratio:
9 (smooth yellow) : 3 (smooth green) : 3 (wrinkled yellow) : 1 (wrinkled green)
25
EXERCISE -PAIRWORK
Match the words with the correct definitions
1
2
3
4
5
6
7
8
9
10
inheritance
chromosomes
gametes
haploid number
diploid number
alleles
dominant
genotype
recessive
phenotype
1
2
a) Number of chromosomes found in a gamete
b) Different forms of a gene
c) Process by which genetic information is passed on from
parents to their offspring
d) A characteristic that can be seen
e) Trait that can be seen only in homozygous recessive form
f) The genes for a particular characteristic
g) Thread-like structures made up of DNA and proteins
h) Number of chromosome found in a normal cell
i) Sex cells which only have half the usual number of
chromosomes
j) Trait that can be seen both in homozygous and in heterozygous
organisms
3
4
5
6
7
8
9
10
26
INCOMPLETE DOMINANCE
Incomplete dominance occurs when no trait
dominates on the other; the heterozygous
is different from the homozygous dominant
because an intermediate trait shows up in
the heterozygous organism.
Example: red snapdragon plant (RR) crossed
with a white snapdragon plant (rr) makes
plants with pink flowers (Rr).
27
CODOMINANCE
Codominance 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 Æ if a person receives A allele and B allele from parents, his blood
type is AB.
28
SEX CHROMOSOMES Æ MALE OR FEMALE?
father
mother
29
DEFECTS IN THE NUMBER OF CHROMOSOMES
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) Æ female with only one X chromosome
• Klinefelter Syndrome (XXY) Æ 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) Æ 90% of affected children die within the first
six months because of heart damage and failure.
• Patau syndrome (trisomy of chr. 13) Æ affected children die within the first three
months because of damage to the nervous system and heart failure.
• Down Syndrome (trisomy of chr.21) Æ affected children show mental retardation and
delay in physical growth. Many children with Down syndrome are educated in regular school
classes while others require specialised educational facilities. Education and proper care
has been shown to improve quality of life significantly. Many adults with Down Syndrome
are 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.
30
GENETIC DISORDERS
AUTOSOMAL DOMINANT =
Mutation occurs in the dominant allele
(A*)Æ Both homozygous dominant
(A*A*) and heterozygous (AA*)
individuals are sick
Ex. Huntington’s disease
X-LINKED DOMINANT = Mutation
occurs in an allele on the X chromosome
(X*):
X*X* Æ homozygous female, sick
X*X Æ heterozygous female, sick
X*Y Æ male, sick
Ex. Rett syndrome
AUTOSOMAL RECESSIVE =
Mutation occurs in the recessive allele (a*)
Æ Homozygous recessive (a*a*) individual
is sick; heterozygous (Aa*) is carrier.
Ex. Albinism; sickle-cell anemia; cystic
fibrosis; Tay-Sachs syndrome.
X-LINKED RECESSIVE =
Mutation occurs in an allele on the X
chromosome (X*):
X*X* Æ homozygous female, sick
X*X Æ heterozygous female, carrier
X*Y Æ male, sick
Ex. Duchenne muscolar dystrophy; haemophilia;
color blindness (daltonism)
Y-LINKED = Mutation occurs in an allele on the Y chromosome
(Y*):
XY Æ healthy male
XY* Æ sick male
31
THE SICKLE-CELL ANEMIA
HbAHbS
HbAHbA
HbAHbS
HbAHbS
HbSHbS
The heterozygous HbAHbS shows an
advantage in case of malaria: Plasmodium
falciparum does not live in sickle cell,
therefore heterozygous individuals are not
affected by malaria.
32
ALBINISM Æ NOT ONLY A HUMAN CONDITION
Albinism (from Latin “Albus” = white) is caused by a genetic mutation of a gene coding for
an enzyme involved in the production of melanin in skin, eyes and hair.
33
COLOUR BLINDNESS (DALTONISM)
Colour blindness or colour vision deficiency is the inability or decreased ability to see
colours, 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 his
own colour blindness.
Because of Dalton's work, the general condition has been called daltonism.
Vision is allowed by photoreceptors called cone cells (active
in 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.
COLOUR BLINDNESS TEST
34
HAEMOPHILIA AND THE
ENGLISH ROYAL FAMILY
Haemophilia is caused by a mutation in the gene coding
for the clotting factor VIII. Such mutation causes
problems during blood clotting after injures.
Since this recessive gene is encoded in the X
chromosome, males can be healthy or sick; females are
carriers.
35
WORKING ON LANGUAGE:
The passive form of the verbs
GRAMMAR REVIEW: in many scientific reports, the use of the passive form of the verbs
is very common.
Exercise Æ 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.
36
......................................................................................................................................................................
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 ......................factor
VIII
....................................................................................................................................................................
37
ACTIVITY Æ 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 dominant
‰ Autosomic recessive
‰ X-linked
‰ Y-linked
Motivate your answer.
...........................................
...........................................
............................................
............................................
...........................................
............................................
38
TASK-BASED ACTIVITY
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:
9 Recent discoveries on gene therapy
9 Relation between genetics and cancer
9 Description of a genetic disorder
Students can find the above information by consulting science
textbooks, other books, internet.
Bibliography and sitography must be included in the presentation.
Language skills
Oral activity Æ speaking in small groups / with whole class
Written activity Æ powerpoint presentation
Use of content-specific language
39
BIBLIOGRAPHY and SITOGRAPHY
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
Websites
http://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/cells
http://www.bbc.co.uk/scotland/learning/bitesize/standard/biology/investigating_cells/
cells_and_diffusion_rev2.shtml
http://www.cellsalive.com/cell_cycle.htm
http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter2/animation__mitosis_and_cytokine
sis.html
http://www.cellsalive.com/mitosis.htm
http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa_pre_2011/celldivision/
http://www.cellsalive.com/puzzles/mitosis/index.html
http://science.education.nih.gov/supplements/nih1/cancer/activities/activity2_animatio
ns.htm
40
https://wikispaces.psu.edu/display/bio110/Home