10.1 Meiosis

Essential idea: Meiosis leads to independent assortment of chromosomes and unique composition of alleles in daughter cells.

The family portrait shows large amounts of variation within a family despite sharing a lot of genes. This shows the potential of crossing over and independent assortment to create near infinite variation in gametes and hence in offspring too.

Understandings, applications and skills

10.1.U1	Chromosomes replicate in interphase before meiosis.
10.1.U2	Crossing over is the exchange of DNA material between non-sister homologous chromatids.
10.1.U3	Crossing over produces new combinations of alleles on the chromosomes of the haploid cells.
10.1.U4	Chiasmata formation between non-sister chromatids can result in an exchange of alleles.
10.1.U5	Homologous chromosomes separate in meiosis I.
10.1.U6	Sister chromatids separate in meiosis II.
10.1.U7	Independent assortment of genes is due to the random orientation of pairs of homologous chromosomes in meiosis I.
10.1.S1	Drawing diagrams to show chiasmata formed by crossing over. [Diagrams of chiasmata should show sister chromatids still closely aligned, except at the point where crossing over occurred and a chiasma was formed.]

[Text in square brackets indicates guidance notes]

Presentation and notes

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Vocabulary

Correct use of terminology is a key skill in Biology. It is essential to use key terms correctly when communicating your understanding, particularly in assessments. Use the quizlet flashcards or other tools such as learn, scatter, space race, speller and test to help you master the vocabulary.

This quizlet is a contribution from Melissa Pain

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Quick quiz

Quick quiz Use the BioK Quick Quiz on 10.1 Meiosis (as directed) to check your understanding of the topic.

Weblinks

Phases of Meiosis
Phases of Meosis by the Khan academy
Meiosis by St Olaf
Meosis by Biostudio

Random Orientation and Independent Assortment
Random Orientation by McGraw and Hill
Independent Assortment by Sumanas Inc.

Nature of science

Making careful observations—careful observation and record keeping turned up anomalous data that Mendel’s law of independent assortment could not account for. Thomas Hunt Morgan developed the notion of linked genes to account for the anomalies. (1.8)