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3.1 Genes

IB Syllabus Statements

Understandings: 

  • A gene is a heritable factor that consists of a length of DNA and influences a specific characteristic.

  • A gene occupies a specific position on a chromosome.

  • The various specific forms of a gene are alleles.

  • Alleles differ from each other by one or only a few bases.

  • New alleles are formed by mutation.

  • The genome is the whole of the genetic information of an organism.

  • The entire base sequence of human genes was sequenced in the Human Genome Project.

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Applications and skills:

  • Application: 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.

  • Application: Comparison of the number of genes in humans with other species.

  • Skill: Use of a database to determine differences in the base sequence of a gene in two species.

Videos

Chromosomes, genes, and alleles

Human Genome Project

Databases for comparing genes

Gene Mutations and Sickle-cell Anemia

Comparing the number of genes

Gene sequencers

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Topic 3.1 Genes SSaQ (Syllabus Statement as Questions)

  • Define gene.

  • What does a gene locus refer to?

  • Describe the relationship between the terms gene and allele.

  • Alleles differ from each other in what way?

  • Describe how new alleles can be formed.

  • What is meant by the genome? Explain why it is not the same as the number of genes.

  • Outline the outcome of the Human Genome Project.

  • Explain what gene sequencer technology is used for.

  • Explain the causes of sickle cell anemia using the following terms: base substitution mutation, mRNA, polypeptide, hemoglobin

  • Using a few examples including humans, plants and bacteria, and, compare the number of genes in humans with other species.

  • Explain how you could use a database such as the Genbank to determine differences in the base sequence of a gene in two species. What additional information could use of such a database provide you with?

  • What specific base substitution causes glutamic acid to be substituted by valine in the sixth amino acid in the hemoglobin polypeptide that is responsible for sickle-cell anemia?

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