General Terms

• Meiosis is a type of cell division that produces four haploid daughter cells from one diploid parent cell, it is also called as reduction division
• gametes are an organism's reproductive cells, referred also as sex cells
• Karyotype is an individual's complete set of chromosomes, including the number and arrangement of chromosomes
• the last pair of chromosomes determines the sex of the individual. Males have xy chromosomes and female has xx chromosomes.
• homologous pair have the same genes in the same order, controlling the same characteristics
• Mitosis produces diploid cells (2n). 2n means two copies of every chromosome
• Meiosis produces haploid cells represented by n
• autosomes are the first 22 pairs of chromosomes in the human body
• the last pair of chromosome is called the sex chromosomes
• There are 5 stages in prophase I: Leptotene, Zygotene, Pachytene, Diplotene, Diakinesis
• there are two stages of meiosis: meiosis I and meiosis II
• There are four stages in Meiosis I: Prophase I, Metaphase I, Anaphase I, and Telophase I
• There are four stages in Meiosis II: Prophase II, Metaphase II, Anaphase II, Telophase II
• Leptotene in prophase I is the stage where the initiation of chromosome condensation takes place and it attains a composite form
• Zygotene in prophase I is the stage where each chromosomes pairs and binds up with their homologous pair
• Pachytene in prophase I is the stage where the crossing over of non-sister chromatids of homologous chromosomes takes place, and they still stay associated at the crossing over sites
• recombinant chromosomes are chromosomes carrying genes from two chromosomes
• Diplotene in prophase I, it marks the synaptonemal complex dissolution and separation of the homologous chromosomes except at the crossing over sites. The formation of X-shaped compositions takes place at the time of separation called chiasmata.
• The areas in the chromosomes where the crossing over occurred are called chiasmata
• Diakinesis in prophase I, it is signified by the end of chiasmata and assembly of the meiotic spindle to distinguish the homologous chromosomes. The disappearance of nucleolus takes place and the nuclear envelope dissociates.
• In metaphase I, the homologous chromosomes line up at the equator and attach to spindle fibers at opposite poles
• In anaphase I, spindle fibers separate the homologous chromosomes in each tetrad and pull them to opposite polls of the cell
• In telophase I, it still contains one chromosome from each homologous pair at separate poles; however, each chromosomes still consists of sister chromatids (these sister chromatids are no longer identical because of the exchange in alleles that happened during crossing over). Afterwards, spindle fiber disappear and the nuclear membrane reforms around the chromosomes, then cytokinesis occurs.
• In prophase II, the nuclear membrane disappears and spindle fibers fan out from the two sets of paired centrioles
• In metaphase II, the chromosomes in each cell line up at the equator and attach to spindle fibers from both poles
• In anaphase II, the sister chromatids of each chromosomes separate and move to opposite poles. Once the sister chromatids separate they are called chromosomes
• In telophase II, the spindle fibers disappear and nuclear membranes reform, and cytokinesis occurs in both cells
• Meiosis II ends up with 4 genetically different haploid daughter cells. Each containing only one set of chromosomes
• Meiosis I ends with 2 genetically different haploid daughter cells. Each haploid cell contains only one set of chromosomes consisting of paired sister chromatids
• Synapsis is the pairing of homologous chromosomes
• Tetrad is a 4 sister chromatids of paired homologous chromosomes
• Crossing over is the exchange of genetic material between homologous chromosomes during meiosis