IB Biology - teaching & learning resources

Topic 4: Genetics (15 hours)

4.1Chromosomes, genes, alleles and mutations

2 hours

Assessment statement

Obj

Teacher’s notes

4.1.1

State that eukaryote chromosomes are made of DNA and proteins.

1

The names of the proteins (histones) are not required, nor is the structural relationship between DNA and the proteins.

4.1.2

Define gene, allele and genome.

1

Gene: a heritable factor that controls a specific characteristic. (The differences between structural genes, regulator genes and genes coding for tRNA and rRNA are not expected at SL).

Allele: one specific form of a gene, differing from other alleles by one or a few bases only and occupying the same gene locus as other alleles of the gene.

Genome: the whole of the genetic information of an organism.

4.1.3

Define gene mutation.

1

The terms point mutation or frameshift mutation will not be used.

4.1.4

Explain the consequence of a base substitution mutation in relation to the processes of transcription and translation, using the example of sickle-cell anemia.

3

GAG has mutated to GTG causing glutamic acid to be replaced by valine, and hence sickle-cell anemia.

Sickle Cell Worksheet essay question.

 

4.2Meiosis

3 hours

Assessment statement

Obj

Teacher’s notes

4.2.1

State that meiosis is a reduction division of a diploid nucleus to form haploid nuclei.

1

4.2.2

Define homologous chromosomes.

1

4.2.3

Outline the process of meiosis, including pairing of homologous chromosomes and crossing over, followed by two divisions, which results in four haploid cells.

2

Limit crossing over to the exchange of genetic material between non-sister chromatids during prophase I. Names of the stages are required.

4.2.4

Explain that non-disjunction can lead to changes in chromosome number, illustrated by reference to Down syndrome (trisomy 21).

3

The characteristics of Down syndrome are not required.

4.2.5

State that, in karyotyping, chromosomes are arranged in pairs according to their size and structure.

1

4.2.6

State that karyotyping is performed using cells collected by chorionic villus sampling or amniocentesis, for pre-natal diagnosis of chromosome abnormalities.

1

Aim 8: There are ethical and social issues associated with karyotyping of unborn fetuses ?

 

4.2.7

Analyse a human karyotype to determine gender and whether non-disjunction has occurred.

3

Karyotyping can be done by using enlarged photographs of chromosomes.

Aim 7: Online simulations of karyotyping activities are available.

4.3Theoretical genetics

5 hours

Assessment statement

Obj

Teacher’s notes

4.3.1

Define genotype, phenotype, dominant allele, recessive allele, codominant alleles, locus, homozygous, heterozygous, carrier and test cross.

1

Do the activity to sort the words from the revision booklet.

4.3.2

Determine the genotypes and phenotypes of the offspring of a monohybrid cross using a Punnett grid.

3

The grid should be labelled to include parental genotypes, gametes, and both offspring genotype and phenotype. Questions using Punnet Squares

Aim 7: Genetics simulation software is available.

4.3.3

State that some genes have more than two alleles (multiple alleles).

1

4.3.4

Describe ABO blood groups as an example of codominance and multiple alleles.

2

4.3.5

Explain how the sex chromosomes control gender by referring to the inheritance of X and Y chromosomes in humans.

3

4.3.6

State that some genes are present on the X chromosome and absent from the shorter Y chromosome in humans.

1

4.3.7

Define sex linkage.

1

4.3.8

Describe the inheritance of colour blindness and hemophilia as examples of sex linkage.

2

Both colour blindness and hemophilia are produced by a recessive sex-linked allele on the X chromosome. Xb and Xh is the notation for the alleles concerned. The corresponding dominant alleles are XB and XH.

4.3.9

State that a human female can be homozygous or heterozygous with respect to sex-linked genes.

1

4.3.10

Explain that female carriers are heterozygous for X-linked recessive alleles.

3

4.3.11

Predict the genotypic and phenotypic ratios of offspring of monohybrid crosses involving any of the above patterns of inheritance.

3

Aim 8: Statisticians are convinced that Mendel’s results are too close to exact ratios to be genuine.

4.3.12

Deduce the genotypes and phenotypes of individuals in pedigree charts.

3

For dominant and recessive alleles, upper-case and lower-case letters, respectively, should be used. Letters representing alleles should be chosen with care to avoid confusion between upper and lower case.

For codominance, the main letter should relate to the gene and the suffix to the allele, both upper case. For example, red and white codominant flower colours should be represented as CR and Cw, respectively. For sickle-cell anemia, HbA is normal and Hbs is sickle cell.

4.4Genetic engineering and biotechnology

5 hours

Assessment statement

Obj

Teacher’s notes

4.4.1

Outline the use of polymerase chain reaction (PCR) to copy and amplify minute quantities of DNA.

2

Details of methods are not required.

4.4.2

State that, in gel electrophoresis, fragments of DNA move in an electric field and are separated according to their size.

1

4.4.3

State that gel electrophoresis of DNA is used in DNA profiling.

1

4.4.4

Describe the application of DNA profiling to determine paternity and also in forensic investigations.

2

Online activities on genetic engineering

Aim 8: There is a variety of social implications stemming from DNA profiling,

TOK: A comparison could be made between blood groups and DNA profiles in their potential for determining paternity.

4.4.5

Analyse DNA profiles to draw conclusions about paternity or forensic investigations.

3

The outcomes of this analysis could include knowledge of the number of human genes, the location of specific genes, discovery of proteins and their functions, and evolutionary relationships.

Aim 7: Online bioinformatics simulations are available.

Aim 8: We can either emphasize the large shared content of the human genome, which is common to all of us and should give us a sense of unity, or we can emphasize the small but significant allelic differences that create the biodiversity within our species, which should be treasured.

 

4.4.6

Outline three outcomes of the sequencing of the complete human genome.

2

4.4.7

State that, when genes are transferred between species, the amino acid sequence of polypeptides translated from them is unchanged because the genetic code is universal.

1

Aim 8: There is an ethical or moral question here: whether it is right to change the genetic integrity of a species by transferring genes to it from another species. The discussion could include the wider question of selective breeding of animals, and whether this is distinctively different and always acceptable. The possibility of animals suffering as a result of genetic modification could be considered.

4.4.8

Outline a basic technique used for gene transfer involving plasmids, a host cell (bacterium, yeast or other cell), restriction enzymes (endonucleases) and DNA ligase.

2

The use of E. coli in gene technology is well documented. Most of its DNA is in one circular chromosome, but it also has plasmids (smaller circles of DNA). These plasmids can be removed and cleaved by restriction enzymes at target sequences. DNA fragments from another organism can also be cleaved by the same restriction enzyme, and these pieces can be added to the open plasmid and spliced together by ligase. The recombinant plasmids formed can be inserted into new host cells and cloned.

4.4.9

State two examples of the current uses of genetically modified crops or animals.

1

Examples include salt tolerance in tomato plants, synthesis of beta-carotene (vitamin A precursor) in rice, herbicide resistance in crop plants and factor IX (human blood clotting) in sheep milk.

Aim 8: The economic benefits of genetic modification to biotechnology companies that perform it could be considered. Also mention the possibility that harmful changes to local economies could result.

4.4.10

Discuss the potential benefits and possible harmful effects of one example of genetic modification.

3

Aim 8: There are ethical questions here about how far it is acceptable for humans to change other species, as well as other ecosystems, in order to gain benefit for humans.

TOK: This is an opportunity to discuss how we can assess whether risks are great enough to justify banning techniques and how the scientific community can inform communities generally about potential risks. Informed decisions need to be made but irrational fears should not be propagated.

4.4.11

Define clone.

1

Clone: a group of genetically identical organisms or a group of cells derived from a single parent cell.

4.4.12

Outline a technique for cloning using differentiated animal cells.

2

Aim 8: Ethical questions about cloning should be separated into questions about reproductive cloning and therapeutic cloning. Some groups are vehemently opposed to both types.

4.4.13

Discuss the ethical issues of therapeutic cloning in humans.

3

Therapeutic cloning is the creation of an embryo to supply embryonic stem cells for medical use.

 

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