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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La Côte International School
IB Biology Unit 10- Genetics and Evolution
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Unit 10.1
• Meiosis undergoes division twice to produce 4 haploid
daughter cells with 23 chromosomes each.
• Chromosomes replicate during the S phase of interphase.
• Prophase I: Chromosomes condense, nuclear
membrane dissolves, homologous chromosomes
form bivalents, crossing over occurs resulting in
genetic variation.
• Metaphase I: Spindle fibres attach to centromeres
of bivalents and align them along the middle of the
cell randomly.
• Anaphase I: Spindle fibres contract and
homologous chromosomes move to opposite
sides.
• Telophase I: Nuclear envelopes form and sister
chromatids decondense, cytokinesis occurs
resulting in 2 diploid cells.
• The same process occurs again known as Meiosis II, except this separates the sister
chromatids, producing 4 haploid daughter cells.
• Independent assortment of genes is due to the random orientation of pairs of homologous
chromosomes in metaphase I.
• Bivalents can form a chiasmata between non-sister chromatids which results in the crossing
over of genes in prophase I. This allows the exchange of genetic information and form
recombinant chromatids.
• Trisomy can occur in anaphase I or II where non-disjunction occurs and either the bivalent or
sister chromatid does not split. This causes Downs Syndrome.
Unit 10.2
• Dihybrid crosses are used to determine the genotype
and phenotype of offspring for two particular genes
that are unlinked.
• When given the genotype of both genes, the possible
gametes must be found using the FOIL method. Then,
these gametes can be crossed.
• Heterozygous genotypes produce a 9:3:3:1 ratio within
a dihybrid cross.
• When performing a test cross to determine a certain
genotype, the unknown must always be crossed with a
homozygous recessive genotype.
• Linked genes are represented as vertical pairs:
• They tend to be inherited together because they have a similar loci on the same chromosome
and therefore do not follow independent assortment.
• In the example given above, the only gametes produced are AB and ab as the genes are linked.
• These gametes are then crossed normally using a punnet grid.
• Genes can also be sex-linked if they are located on the X or Y chromosome.
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