Question

In meiosis, synapsis occurs during
A. S-phase
B. Interphase
C. Metaphase
D. Prophase 1

Answer 1

Synapsis is pairing of homologous chromosomes for crossing over. This process is supported by the formation of the synaptonemal complex. In other words, homologous chromosomes match with each other before segregation and crossing over. It occurs in the meiosis I stage.

Complete answer: When homologous chromosomes pair during meiosis, it is called synapsis. Firstly, the ends of chromosomes attach to the nuclear envelope and then migrate until matching ends pair with each other. This process is supported by the extranuclear cytoskeleton. Intervening regions are now connected by a complex called synaptonemal complex made up of proteins and RNA. Synapsis occurs in prophase 1 of meiosis. Synapsis leads to the pairing of homologous chromosomes and crossing over between them. Crossing over is the exchange of genetic material between homologous chromosomes. In autosomes during synapsis, the whole length of chromosomes are held together by synaptonemal complex while in sex chromosomes synaptonemal complex is present only at one end of sex chromosome.
Hence, the correct answer is option D.

Additional information: In female Drosophila melanogaster, synapsis occur without recombination. Other steps of meiosis I are as prophase I, metaphase I, anaphase I, telophase I and cytokinesis.

Note: Meiosis is a type of reductional cell division and produces four haploid daughter cells. It mainly occurs in germ cells. It mainly consists of meiosis I and II. Stages of Meiosis II consists of prophase II, metaphase II, Anaphase II, Telophase II, cytokinesis II.