Prophase I
Table of Contents
Definition
- longest and most complex phase (90%).
- Chromosomes condense.
- Nucleus and nucleolus disappear.
- Spindle forms.
Homologous chromosomes
- Non-sister chromatids that have homologous regions code for the same gene.
Synapsis
- an event when the homologous chromosomes/pairs come together and exchange information.
- You can also call these pairs as "Tetrad" which consists of two chromosomes or four chromatids.
- The synaptonemal complex adjoins each strand of DNA to its correct position.
Crossing Over
- It occurs between non-sister chromatids
- segments of non-sister chromatids break and reattach to the other chromatid.
- causes genetic recombination.
Sex Chromosomes
- XX chromosome for female
- XY chromosome for male
Sub-stages
Leptotene
- The chromosomes begin to condense
Zygotene
- Synapsis begins with a synaptonemal complex forming between homologous chromosomes.
Pachytene
- Crossing over of genetic material occurs between non-sister chromatids
Diplotene
- Synapsis ends with disappearance of synaptonemal complex
- homologous pairs remain attached at chiasmata
Diakinesis
- Chromosomes become fully condensed and nuclear membrane disintegrates prior to metaphase I