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Class notes Biology Oxford IB Diploma Programme: Biology Course Companion
IBDP HL Biology - 2.2 Water Notes
Summary of the entire Biology book from the IB diploma
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3.1 Genes
Essential idea
Every living organism inherits a blueprint for life from its parents.
Objectives
Describe what is meant by a gene.
Explain how mutations can bring about new copies of genes.
Compare gene numbers in humans and other organisms.
Key words: gene / allele / genome / mutation / sickle cell / base substitution / locus
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.
Applications
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.
Comparison of the number of genes in humans with other species.
Skills
Use of a database to determine differences in the base sequence of a gene in two species.
Genetics is the branch of biology concerned with the storage of information in living organisms and how this
information can be passed from parents to progeny.
GENES AND LOCI
,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.
DNA is the genetic blueprint which codes for the characteristics of an organism.
physical, behavioural and physiological features.
packaged and organised into discrete structures called chromosomes.
A gene is a heritable sequence of DNA that encodes for a specific trait.
traits may also be influenced by multiple genes.
linked in groups and each group corresponds to one chromosome pair in a species.
humans have 23 chromosome pairs (46 chromosomes).
the position of a gene on a particular chromosome is called the locus (plural = loci).
ALLELES
The various specific forms of a gene are alleles.
Alleles differ from each other by one or only a few bases.
Alleles are alternative forms of a gene that code for the different variations of a specific trait.
as alleles are alternative forms of the one gene, they possess very similar gene sequences.
only differ from each other by one or a few bases.
occupy the same position on each chromosome of a chromosome pair – same locus.
only one allele can occupy the locus of the gene on each chromosome.
two alleles of a gene is present in a chromosome pair (can be same or different).
SNPs
Positions in a gene where more than one base may be present are called single nucleotide polymorphisms.
abbreviated to SNPs and pronounced snips.
several snips can be present in a gene, but even then the alleles of the gene differ by only a few bases.
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MUTATIONS
New alleles are formed by mutation.
,A gene mutation is a change in the nucleotide sequence of a section of DNA coding for a specific trait.
new alleles are formed by mutation.
can be beneficial, detrimental or neutral.
beneficial (missense) mutations change the gene sequence to create new variations of a trait.
detrimental (nonsense) mutations cut the gene sequence to nullify the normal function of a trait.
neutral (silent) mutations have no effect on the functioning of the specific feature.
GENOME
The genome is the whole of the genetic information of an organism.
The genome is the whole of the genetic information of an organism.
contains the entire base sequence of each of its DNA molecules.
Humans
46 molecules that form the chromosomes in the nucleus plus the DNA molecule in the mitochondrion.
Plants
DNA molecules of chromosomes in the nucleus plus the DNA molecules in the mitochondrion and the
chloroplast.
Prokaryotes
genome is much smaller and consists of the DNA in the circular chromosome, plus any plasmids that are
present.
Human Genome Project
The entire base sequence of human genes was sequenced in the Human Genome Project.
The Human Genome Project (HGP) was an international cooperative venture established in 1990 to sequence the
human genome.
showed that humans share the majority of their sequence, with short nucleotide polymorphisms contributing
diversity.
The completion of the Human Genome Project in 2003 lead to many outcomes:
Mapping – the number, location, size and sequence of human genes is now established.
, Screening – this has allowed for the production of specific gene probes to detect sufferers and carriers of
genetic diseases.
Medicine – the discovery of new proteins have lead to improved treatments (pharmacogenetics and rational
drug design).
Ancestry – comparisons with other genomes have provided insight into the origins, evolution and migratory
patterns of man.
3.2 Chromosomes
Essential idea
Chromosomes carry genes in a linear sequence that is shared by members of a species.
Objectives
Describe the appearance of chromosomes in prokaryotes and eukaryotes.
Analyse and interpret karyograms.
Compare chromosome numbers in different species.
Key words: chromosome / allele / haploid / diploid / homologous / plasmid / autosome
Understandings
Prokaryotes have one chromosome consisting of a circular DNA molecule.
Some prokaryotes also have plasmids but eukaryotes do not.
Eukaryote chromosomes are linear DNA molecules associated with histone proteins.
In a eukaryote species there are different chromosomes that carry different genes.
Homologous chromosomes carry the same sequence of genes but not necessarily the same alleles of
those genes.
Diploid nuclei have pairs of homologous chromosomes.
Haploid nuclei have one chromosome of each pair.
The number of chromosomes is a characteristic feature of members of a species.
A karyogram shows the chromosomes of an organism in homologous pairs of decreasing length.
Sex is determined by sex chromosomes and autosomes are chromosomes that do not determine sex.
Applications
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