Summary Notes designed for the International Baccalaureate Diploma Programme. These notes are detailed yet concise, with all the information to achieve a 7 in IB Biology HL or SL. These notes were made using information from the IB syllabus, Oxford IB Diploma HL Biology Textbook, Bioninja and the B...
Class notes Biology Oxford IB Diploma Programme: Biology Course Companion
IBDP HL Biology - 2.2 Water Notes
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IB Biology Unit 3- Genetics
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Unit 3.1
• A gene is a heritable factor that consists of a length of DNA and influences a specific
characteristic.
• The entire base sequence of human genes was sequenced in the Human Genome Project. The
genome is the whole of the genetic information of an organism
• A gene occupies a specific position on a chromosome known as the gene locus.
• Alleles are different forms of a specific gene such
as having brown or blonde hair. They differ from
each other by only 1 or 2 bases. New alleles are
formed by a mutation.
• Sickle cell anaemia is caused by base substitution
mutation where a thymine is replaced with alanine.
• This causes the haemoglobin to be unable to carry
oxygen properly so the cell develops a sickle
shape.
• Rice has more genes than humans, E. Coli has less. Humans have around 21,000.
Unit 3.2
• Prokaryotes have one chromosome consisting of a circular DNA molecule. They may also have
extra DNA in the form of plasmids.
• Bacterial cells may exchange plasmids via their sex pili, in a process known as bacterial
conjugation.
• Eukaryotic chromosomes are linear DNA molecules associated with histone proteins.
• In humans there are 22 pairs of autosomal chromosomes and one pair of sex chromosomes.
• On a eukaryotic chromosome the p arm is short and the q arm is long. Gene loci are named
based on their chromosome number, arm and band location e.g 7p20.
• Homologous chromosomes (one from each parent) carry the same sequence of genes but not
necessarily the same alleles of those genes.
• Diploid nuclei (2n) have pairs of homologous chromosomes whereas haploid nuclei (n) have one
chromosome of each pair.
• A karyogram shows the chromosomes of an organism in homologous pairs of decreasing
length. They can be used to determine the sex or to identify trisomy (Down’s Syndrome is
trisomy 21).
• The chromosome number does not give an indication of how complex a species is:
Unit 3.3
• During meiosis one diploid nucleus divides to produce four haploid nuclei.
• DNA is replicated before meiosis so that all chromosomes consist of two sister chromatids.
• See Unit 10.1 for stages of meiosis.
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