AHL 10 Genetics

10.1 Meiosis 10.1.1 Describe the behavior of chromosomes during meiosis. Terms: homologous chromosomes synapsis tetrad/ bivalent sister chromatids

10.1.2 Chiasmata

How many chiasmata?

Process of Crossing Over

A cell replicates its DNA and then starts to divide by meiosis A cell replicates its DNA and then starts to divide by meiosis. What is the expected arrangement of chromosomes if crossing over has taken place between the two genes shown?

May 2008 HL Paper 1 Q29 This question revealed some widespread misunderstanding with less than 25% of candidates choosing the correct answer, which was C. Far more chose answer D, which shows a chiasma that has formed by the ends of two chromatids swapping partners. Chiasmata are formed by crossing over, which involves the breakage and rejoining of chromatids or DNA molecules. This is one area where teachers need to ensure that they are teaching the topic correctly.

10.1.3 Genetic variety in gametes Unlimited creativity!

Random Orientation in Metaphase I If having 3 pairs of chromosomes gives rise to 8 combinations of chromosome assortment in gametes, how many combinations would human have for having 23 pairs of chromosomes?

10.1.4 allele pairs separate independently during the formation of gametes

10.1.4 Mendel’s Law of Independent Assortment

10.2 Dihybrid crosses 10.2.1, 2 Linked genes, unlinked genes Autosomes, sex chromosomes