1. Topic 10.1
Meiosis (HL)

2. Use the following animations to help you to discover the behavior
of chromosomes in the different stages of meiosis:

3. 10.1.2 Outline the formation of chiasmata
in the process of crossing over
During prophase I of meiosis, homologous chromosomes come together in pairs.
Each chromosome is divided into 2 chromatids. The homologous chromosomes twist around each other. This creates a tension, which may cause breaks to occur along the length of the chromatids.
During crossing over, corresponding fragments of chromatids may get swapped over.
A chiasma is an X-shaped structure formed between non-sister chromatids during prophase I of meiosis. This chiasma is a physical manifestation of crossing over. Usually between one and three chiasmata form per homologous pair. The chiasmata persist through metaphase I and play a role in the prevention of non-disjunction.
This cutting and sticking of chromatids means that the genetic material is exchanged. In this way, new genetic combinations are produced and variation in the gametes is increased.
So, together with random segregation of chromosomes, crossing over can produce an enormous amount of variation, both in the gametes and the resulting offspring.
This image shows that multiple chiasmata can form within one tetrad.

4. 10.1.3 Explain how meiosis results
in genetic variation

5. 10.1.3 Explain how meiosis results
in genetic variation

6. 10.1.3 Explain how meiosis results
in genetic variation

7. independent assortment
States Mendel’s Law of
independent assortment
Mendel's law of independent assortment, states that allele pairs separate independently during the formation of gametes. This means that traits are transmitted to offspring independently of one another.

8. 10.1.4 Relationship between Mendel’s Law
Of independent assortment and Meiosis