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TOPIC 10 GENETICS. 10.1 Meiosis (overview). 10.1.1: Describe the behaviour of the chromosomes in the phases of meiosis. Prophase I of Meiosis I. Metaphase I of Meiosis I. Anaphase I of Meiosis I. Telophase I of Meiosis I. Prophase II of Meiosis II. Metaphase II of Meiosis II.
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10.1.1: Describe the behaviour of the chromosomes in the phases of meiosis. Prophase I of Meiosis I
10.1.2: Outline the formation of chiasmata in the process of crossing over. 10.1.2: Crossing over
10.1.3: Explain how meiosis results in an effectively infinite genetic variety in gametes through crossing over in prophase I and random orientation in metaphase I.
10.1.3 and 10.1.4.: State Mendel’s law of independent assortment. 10.1.3 and 10.1.4
10.2: Dihybrid Crosses and gene linkage Unlinked genes
10.2.1 ; Calculate and predict the genotypic and phenotypic ratio of offspring of dihybrid crosses involving unlinked autosomal genes.
10.2.2: Distinguish between autosomes and sex chromosomes. 10.2.2: autosomes / sex chromosomes
10.2.3: Explain how crossing over between non-sister chromatids of a homologous pair in prophase I can result in an exchange of alleles. 10.2.3: Crossing over
10.2.4: Define linkage group. A pair or set of genes on a chromosome that tend to be transmitted together.
10.2.5 and 10.2.6: Explain an example of a cross between two linked genes. 10.2.5 and 10.2.6
Identify which of the offspring are recombinants in a dihybrid cross involving linked genes. 10.2.5 and 10.2.6
10.3.1: Define polygenic inheritance. Polygenic Inheritance
10.3.2: Explain that polygenic inheritance can contribute to continuous variation using two examples, one of which must be human skin colour.
AaBb A a A a ? OR B b B b
Start by assuming that the genes are unlinked because you know what would be the expected ratios of offspring AaBb A a B b AB Ab aB ab
AaBb x AaBb A a B b AB Ab aB ab
AaBb x AaBb A a B b AB Ab aB ab
AaBb A a B b AB Ab aB ab
AaBb X AaBb A a B b A a B b AB Ab aB ab AB Ab aB ab
AB Ab aB ab AABB AABb AaBB AaBb AABb Aabb AaBb Aabb AaBB AaBb aaBB aaBb AaBb Aabb aaBb aabb AB Ab aB ab A______ B_____ = 9/16 1125 620 A______ bb = 3/16 375 702 aa B_____ = 3/16 375 503 aa bb = 1/16 125 400
What are the expected phenotype ratios if the genes are unlinked in the following crosses? Then determine if the genes appear to be linked or unlinked AABb X AAbb AaBB X aaBb aaBb X Aabb