Question

What happens to homologs in zygotene and pachytene?

Answer 1

Homologs in zygotene:

1. Zygotene is the second step of prophase-1 meiosis.
2. It is preceded by the leptotene stage, during which chromosomes uncoil and condense.
3. Homologous chromosomes (one from the mother and one from the father) unite and marry at the zygotene stage.
4. The pairing of homologous chromosomes is known as synapsis.
5. The synaptonemal complex, a protein complex, links the paired chromosomes.
6. The pair of homologous chromosomes is now referred to as tetrad or bivalent.
7. The number of bivalents is half the number of chromosomes in the cell at the start.
8. Each bivalent contains one chromosome from each parent.

Homologs in pachytene:

1. The Pachytene stage comes after Zygotene.
2. Pachytene is the third stage of prophase-1 meiosis.
3. The tetrad generated by synapsis becomes apparent in the pachytene stage, and four chromatids are plainly visible.
4. In each tetrad, four kinetochores are present.
5. At this stage, recombination or crossing across occurs.
6. In this procedure, genetic material is exchanged between non-sister chromatids of homologous chromosomes.
7. At the point of crossing over, recombination nodules develop and homologous chromosomes are joined to one another.