Chapter 10, Problem 3A

Summary Introduction

To write:

Correct vocabulary term for the given definition.

Introduction:

In animals the sexual life cycle involves meiosis. In order to maintain the same number of chromosomes in each generation, an organism produces gametes. Gametes are sex cells and have half the number of chromosomes. When gametes combine in fertilization, the number of chromosomes is restored.

Answer to Problem 3A

Crossing over

Explanation of Solution

Meiosis involves two consecutive cell divisions called meiosis I and meiosis II. In meiosis I the stages are interphase I, prophase I, metaphase I, anaphase I and telophase I. during interphase I cells carry out cellular activities, replication of DNA and synthesis of proteins.

During prophase I, the replicated chromosomes appear as two sister chromatids. The homologous chromosomes condense and begin to form pairs in a process called synapsis. The homologous chromosomes are held tightly together along their lengths. Some segments of homologous chromosomes get exchanged during synapsis. This process is called crossing over. It is a process during which chromosomal segments are exchanged between a pair of ofhomologous chromosomes. This results in exchange of genes between homologous chromosomes.