Give me the detail information of meiosis (all stages)
Answers
Meiosis consists of two divisions, both of which follow the same stages as mitosis (prophase, metaphase, anaphase, telophase)
Meiosis is preceded by interphase, in which DNA is replicated to produce chromosomes consisting of two sister chromatids
A second growth phase called interkinesis may occur between meiosis I and II, however no DNA replication occurs in this stage
Meiosis I
The first meiotic division is a reduction division (diploid → haploid) in which homologous chromosomes are separated
P-I: Chromosomes condense, nuclear membrane dissolves, homologous chromosomes form bivalents, crossing over occurs
M-I: Spindle fibres from opposing centrosomes connect to bivalents (at centromeres) and align them along the middle of the cell
A-I: Spindle fibres contract and split the bivalent, homologous chromosomes move to opposite poles of the cell
T-I: Chromosomes decondense, nuclear membrane may reform, cell divides (cytokinesis) to form two haploid daughter cells
Meiosis II
The second division separates sister chromatids (these chromatids may not be identical due to crossing over in prophase I)
P-II: Chromosomes condense, nuclear membrane dissolves, centrosomes move to opposite poles (perpendicular to before)
M-II: Spindle fibres from opposing centrosomes attach to chromosomes (at centromere) and align them along the cell equator
A-II: Spindle fibres contract and separate the sister chromatids, chromatids (now called chromosomes) move to opposite poles
T-II: Chromosomes decondense, nuclear membrane reforms, cells divide (cytokinesis) to form four haploid daughter cells
The final outcome of meiosis is the production of four haploid daughter cells
These cells may all be genetically distinct if crossing over occurs in prophase I (causes recombination of sister chromatids)
Meiosis is the process in eukaryotic, sexually-reproducing animals that reduces the number of chromosomes in a cell before reproduction. Many organisms package these cells into gametes, such as egg and sperm. The gametes can then meet, during reproduction, and fuse to create a new zygote. Because the number of alleles was reduced during meiosis, the combination of two gametes will yield a zygote with the same number of alleles as the parents. In diploid organisms, this is two copies of each gene.
PHASES OF MEIOSIS
Before meiosis, the DNA is replicated, as in mitosis. Meiosis then consists of two cell divisions, known as meiosis Iand meiosis II. In the first division, which consists of different phases, the duplicated DNA is separated into daughter cells. In the next division, which immediately follows the first, the two alleles of each gene are separated into individual cells. The following are descriptions of the two divisions, and the various phases, or stages of each meiosis. Remember, before meiosis starts the normally diploid DNA has been duplicated. This means there are 4 copies of each gene, present in 2 full sets of DNA, each set having 2 alleles. In the diagram below, the red chromosomes are the ones inherited from the mother, the blue from the father. In the start of the following diagram, the DNA has already been replicated, which is why the red and blue chromosomes look like the letter “X”. Each one of these “X” chromosomes consists of two sister chromatids, or cloned DNA from replication. They are connected at the centromere for storage, but can separate into individual chromosomes