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Summary IB Biology Topic 3: Genetics
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  • Module
  • Biology SL and HL
  • Institution
  • International Baccalaureate Diploma
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  • IB Biology Course Book

Detailed objective-by-objective summary notes for Topic 3: Genetics for IB Biology SL/HL. Contains information on everything you need to know from 3.1 to 3.5, according to each understanding, application or skill. Written by a IB HL Biology student who graduated with a 45/45.

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  • March 5, 2019
  • 12
  • 2016/2017
  • Summary

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  • biology
  • ib biology
  • genetics
  • topic 3
  • ib
  • international baccalaureate
  • hl
  • sl

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  • Biology SL and HL
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IB TOPIC 3 | GENETICS
2016 | SYJ0014


Topic 3.1: Genetics – Genes
Every living organism inherits a blueprint for life from its parents.

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

 Gene: heritable factor consisting of short segment of DNA that influences a specific characteristics found on a specific position
 One chromosome may contain thousands of genes; there are only 46 DNA molecules but thousands of genes in humans

• Understanding: A gene occupies a specific position on a chromosome.

 Locus: specific position each gene occupies a specific position on its respective type of chromosome
 Locus and linked genes: the closer the genes are to each other, the more likely they will be linked

• Understanding: The various specific forms of a gene are alleles.

 Alleles: alternative forms of the same gene that occupy the same position (loci) on homologous chromosome
 Example: genes for coat colour in mice (yellow, grey, black etc.)

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

 The variation of genes (in forms of alleles) exist by the variation in the base sequence

 Single nucleotide polymorphism (SNPs): DNA sequence variation occurring when a single nucleotide in a shared sequence differs between
members of a species or paired chromosomes in an individual
 Genes and SNP: several SNPs can be present in one gene (alleles), but they only differ by few bases

• Understanding: New alleles are formed by mutation.

 Mutation: permanent, random changes in the sequence of nucleotides in DNA
 All new alleles are formed by random mutations
 Mutations are most likely harmful and often results in death of the organism, but sometimes it may be beneficial

 Point mutation: mutation where a single nucleotide or a triplet of nucleotide is altered
 Alternately known as: base substitution mutation
 Character: point mutation usually only affects one gene

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

 Genome: entire genetic information of an organism
 Includes: the genes in mitochondria (eukaryotes), chloroplasts (plants), and any plasmids (prokaryotes)

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

 Human Genome Project (HGP): international scientific project determining the sequence of nucleotide base pairs of human DNA
 Period of project: 13 years (1990-2003)
 Current objective: current stage is to find variable between different individuals and identify the function of the genes

• Application: The causes of sickle cell anaemia, 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 haemoglobin.

 Sickle-cell anaemia: common genetic disease that causes haemoglobin to change into a sickle shape in low oxygen concentration

 Cause of sickle cell anaemia:
 Base substitution mutation: A to T (GAG to GTG)
 Change in base sequence of mRNA: glutamic acid (GAG) to valine (GUG) for the sixth amino acid
 Change in polypeptide: causes haemoglobin molecules to stick together in low oxygen

 Consequences of sickle cell anaemia:
 Tissue damage: causes damage to tissues by becoming trapped in blood capillaries
 RBC loss: Plasma membrane and haemoglobin are damaged and life of a red blood cell can be shortened
 Immunity to malaria: individuals with sickle cell anaemia is immune to malaria

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

Name of species Number of genes
Homo sapiens (humans) <22,500
Oryza sativa (rice) 46,000
Mus musculus (mice) 30,000
Drosophila melanogaster (fruit flies) 14,000
Escherichia coli 4,403

• Skill: 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 has use in reclassifying organisms into three organism domains



LAST EDITED 2017-03-15 | 1

, IB TOPIC 3 | GENETICS
2016 | SYJ0014


• Nature of science: Developments in scientific research follow improvements in technology—gene sequencers are used for the sequencing of
genes.

• 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.
• Guidance: 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.
• Guidance: 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.
• Guidance: 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.
• Guidance: Deletions, insertions and frame shift mutations do not need to be included.




LAST EDITED 2017-03-15 | 2

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