Crossing Over and Independent Assortment of Alleles 1.
Which of the following statements are TRUE and which are FALSE? If the statement is false, write a true version of it next to it. a. Crossing over takes place when the bivalents are lined up along the cell equator during metaphase I. b. Crossing over produces new combinations of alleles. c. During crossing over, chromatids receive new genes. 2.
The diagram below shows the process of crossing over in a bivalent. Label the following things: a homologous pair of chromosomes, a pair of sister chromatids, two non­sister chromatids, a chiasma. 3.
Below is a diagram showing four bivalents lined up on the cell equator during metaphase I of meiosis in drosophila. Copyright George Weller 2016 For more notes and resources, visit www.georgeweller.net a.
How many chromosomes are present in the cell? b.
How many chromatids are present in the cell? c.
How many homologous pairs of chromosomes are present in the cell? d.
Chromosome 2A has been labelled. Work out the positions of all of the other chromosomes in the cell and complete the labels for them (1A, 1B, 2B, 3A, 3B, 4A and 4B). Use the following information to help you: When the chromosomes are pulled to the poles of the cell during anaphase I, chromosomes 2A and 4A segregate together, chromosomes 1B and 4B segregate together, and chromosomes 1A and 3B segregate together. e.
How many other possible ways are there of arranging these chromosomes at metaphase I? 4.
The previous question demonstrated that the random assortment and segregation of chromosomes during meiosis I leads to variation. Name three other processes that occur during meiosis and fertilisation that lead to variation. Copyright George Weller 2016 For more notes and resources, visit www.georgeweller.net