Essential idea: Every living organism inherits a blueprint for life from its parents.
Genes and hence genetic information is inherited from parents, but the combination of genes inherited from parents by each offspring will be different. In sexual reproduction each parent can only pass on 50% of there genes as the other 50% comes from the second parent.
N.B. One of the most remarkable facts about genes is how alleles show very few changes in bases and cause such large change in phenotypes (characteristics). For instance humans share 50% of their genes with bananas.
N.B. One of the most remarkable facts about genes is how alleles show very few changes in bases and cause such large change in phenotypes (characteristics). For instance humans share 50% of their genes with bananas.
Understandings, applications and skills
| 3.1.U1 | A gene is a heritable factor that consists of a length of DNA and influences a specific characteristic. |
| 3.1.U2 | A gene occupies a specific position on a chromosome. |
| 3.1.U3 | The various specific forms of a gene are alleles. |
| 3.1.U4 | Alleles differ from each other by one or only a few bases. |
| 3.1.U5 | New alleles are formed by mutation. [Deletions, insertions and frame shift mutations do not need to be included.] |
| 3.1.U6 | The genome is the whole of the genetic information of an organism. |
| 3.1.U7 | The entire base sequence of human genes was sequenced in the Human Genome Project. |
| 3.1.A1 | The causes of sickle cell anemia, including a base substitution mutation, a change to the base sequence of mRNA transcribed from it and a change to the sequence of a polypeptide in hemoglobin. [Students should be able to recall one specific base substitution that causes glutamic acid to be substituted by valine as the sixth amino acid in the hemoglobin polypeptide.] |
| 3.1.A2 | Comparison of the number of genes in humans with other species. [The number of genes in a species should not be referred to as genome size as this term is used for the total amount of DNA. At least one plant and one bacterium should be included in the comparison and at least one species with more genes and one with fewer genes than a human.] |
| 3.1.S1 | Use of a database to determine differences in the base sequence of a gene in two species. [The Genbank® database can be used to search for DNA base sequences. The cytochrome C gene sequence is available for many different organisms and is of particular interest because of its use in reclassifying organisms into three domains.] |
[Text in square brackets indicates guidance notes]
Starter
Watch the video where do genes come from by Carl Zimmer
Presentation and notesThe presentation is designed to help your understanding. The notes outline is intended to be used as a framework for the development of student notes to aid revision.
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Weblinks
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Genes and Alleles
3.1 Genes by Stephanie Castle (IB Biology Review) 3.1 Alleles by Stephanie Castle (IB Biology Review)
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Sickle Cell Anaemia
3.1 Application: Sickle cell anaemia by Stephanie Castle (IB Biology Review) Mutations What is mutation? by Learn.Genetics Disease & Mutation: DNA Damage by DNA Learning Center Human Genome Project Timeline of the human genome by Genome: Unlocking Life's Code 3.1 The genome and human genome project by Stephanie Castle (IB Biology Review) |
Nature of science
Developments in scientific research follow improvements in technology—gene sequencers are used for the sequencing of genes. (1.8) [linked to 3.1.U7, 3.1.A1, 3.1.A2, 3.1.S1]
International-mindedness
Sequencing of the human genome shows that all humans share the vast majority of their base sequences but also that there are many single nucleotide polymorphisms that contribute to human diversity.
Theory of knowledge
There is a link between sickle cell anemia and prevalence of malaria. How can we know whether there is a causal link in such cases or simply a correlation?
- Discovery of a correlation in Science is not used as evidence by itself. More commonly a correlation is used to formulate a hypothesis. The hypothesis is then tested to see if an underlying empirical relationship exists, e.g. is the persistance of sickle cell anemia caused by the presence of the malarial parasite.
