Stages of Prophase I Meiosis I Watch on YouTube Learn Medical Health Sciences Dr. Shaista

Watch Full Video on Meiosis Overview: Prophase I the longest stage of meiosis I is further divided into five substages: Leptotene: Chromosomes condense and become visible as thin threads.
Homologous chromosomes start to approach each other but arent paired yet. Zygotene: Homologous chromosomes pair up in a process called synapsis.
A protein structure called the synaptonemal complex forms between them holding them together. Pachytene: The longest substage.
The synaptonemal complex is complete and chromosomes are tightly paired.
Here genetic exchange crossing over happens: non-sister chromatids swap DNA segments increasing genetic diversity. Diplotene: The synaptonemal complex breaks down and homologous chromosomes start to repel slightly except at crossing over points chiasmata which remain visible. Diakinesis: Chromosomes are fully condensed chiasmata move to chromosome ends.
The nuclear envelope breaks down and the meiotic spindle forms preparing for the next stage metaphase I. Meiosis is a two-part cell division process that creates genetically diverse gametes sperm and eggs.
Separates homologous chromosomes paired chromosomes one from each parent and shuffles genetic material. Phases: Similar to mitosis prophase metaphase anaphase telophase with some key differences. Prophase I: Longest phase chromosomes condense homologous chromosomes pair up synapsis and exchange genetic material crossing over. Metaphase I: Paired chromosomes bivalents align at the center of the cell. Anaphase I: Homologous chromosomes separate and move to opposite poles with independent assortment determining which chromosome goes to each daughter cell.
This is where genetic variation is introduced. Telophase I: Nuclear envelope reforms around separated chromosomes resulting in two daughter cells with half the original number of chromosomes haploid. Meiosis II Focus: Separates sister chromatids copies of each chromosome of the haploid cells from Meiosis I. Phases: Similar to mitosis but faster and without a DNA replication step. Prophase II: Chromosomes condense further nuclear envelope breaks down. Metaphase II: Sister chromatids line up at the center of the cell. Anaphase II: Sister chromatids separate and move to opposite poles. Telophase II: Nuclear envelope reforms around separated chromosomes in each daughter cell followed by cytokinesis cytoplasmic division. Outcome: Meiosis I: Two daughter cells with half the number of chromosomes haploid and unique genetic combinations due to crossing over and independent assortment. Meiosis II: Four daughter cells each with a haploid set of chromosomes gametes with further genetic variation due to sister chromatid separation. Key Points: Meiosis I reduces chromosome number and shuffles genes. Meiosis II separates sister chromatids creating four genetically distinct gametes. Meiosis is crucial for sexual reproduction ensuring genetic diversity in offspring. Follow Our Facebook Page:

Источник: rutube.ru