How to count the number of chromosomes and chromatids in meiosis or mitosis? I found this in many past question papers. In order to answer such questions we need to have some basic concepts regarding chromosomes and chromatids. Rest is easy.
Prophase
o Chromosome #: 46
o Chromatid #: 92
Metaphase
o Chromosome #: 46
o Chromatid #: 92
Anaphase: separation of sister chromatids
o Chromosome #: 92
o Chromatid #: 92
Telophase
o Chromosome #: 92
o Chromatid #: 92
Telophase after Cytokinesis or in daughter cells
o Cell= 2n [diploid]
o Chromosome #: 46
o Chromatid #: 46
The key points are
- The number of chromosomes=count the number of centromeres
- The number of DNA molecule = count the number of chromatids
- The number of DNA molecule increases only when DNA replicates that is in the S phase of the cell cycle
- The number of DNA molecules decreases only when the cell divides,
In this figure, chromosome before DNA replication has a single chromatid. After DNA replication in S phase, two chromatids are held at a common centromere representing a single chromosome.
Let us take the case of ours to explain this. You just imagine what happens at each stage. the number of chromosome in each cell is 46
Human cell [2n=46]
G1 Phase
• Chromosome #: 46
• Chromatid #: 46
G2 Phase
DNA replication has already occurred [during S phase]. The number of DNA molecule increases only when DNA replicates that is in the S phase of the cell cycle.
Human cell [2n=46]
G1 Phase
• Chromosome #: 46
• Chromatid #: 46
G2 Phase
DNA replication has already occurred [during S phase]. The number of DNA molecule increases only when DNA replicates that is in the S phase of the cell cycle.
That is, 2 chromatids attached to a common centromere region = 1 chromosome
Therefore Chromosome #: 46
Chromatid #: 92
Mitosis
Therefore Chromosome #: 46
Chromatid #: 92
Mitosis
Prophase
o Chromosome #: 46
o Chromatid #: 92
Metaphase
o Chromosome #: 46
o Chromatid #: 92
Anaphase: separation of sister chromatids
o Chromosome #: 92
o Chromatid #: 92
Telophase
o Chromosome #: 92
o Chromatid #: 92
Telophase after Cytokinesis or in daughter cells
o Cell= 2n [diploid]
o Chromosome #: 46
o Chromatid #: 46
The purpose of mitosis is to make two genetically identical cell. A the beginning of G1, the chromosome and chromatid number is 46. After mitosis, each daughter cell has 46 chromosomes.
Hope everything is clear.
See also: Chromosome and Chromatid count (DNA molecule) in humans during Meiosis
See also: Chromosome and Chromatid count (DNA molecule) in humans during Meiosis
Tags:
Chromatid count in Humans during Mitosis
Chromosome and chromatid
Chromosome number in Humans during Mitosis
count the chromatid
mitosis
mitosis and meiosis notes
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