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Steps of Mitosis

Goal of Mitosis: two daughter cells inherit an equal and identical complement of chromo­somes
3 things that Mitosis does: 1.) develo­pment 2.) growth cell replac­ement 3.) asexual reprod­uction
Interp­hase: Period when cell isn't in non dividing state; consists of G1, S-phase, G2
S-Phase: DNA replic­ation
G1 Phase: the cell grows physically and increases the volume of both protein and organe­lles.
G2 Phase: Organelles and proteins for cell division are produced; Getting ready for Mitosis
Prophase: Conden­sation of chromo­som­es,the movement of the centro­somes, the formation of the mitotic spindle, and the beginning of nucleoli break down
Metaphase: Duplicated chromo­somes move to the middle, spindle fibers connect to centro­meres
Anaphase: Sister chromatids separate from one another and are pulled into opposite poles of the cell
Telophase: Chromo­somes begin to decond­ense, spindle breaks down, nuclear membrane and nucleoli re-form (nuclear envelope)
Cytoki­nesis: splits the parent cell into two identical daughter cells


diploid oogonium go through mitosis until one develops into a primary oocyte, which will begin the first meiotic division, but then arrest (in prophase 1) ; it will finish this division as it develops in the follicle, giving rise to a haploid secondary oocyte and a smaller polar body
- Meiosis starts in fetus
Oogenesis -> 1 haploid, ovum + 2-3 polar bodies

Arrest in Oogensis

• At birth, Primary oocyte, Arrest Prophase I
• Prophase I
arrest in fetal
• Continue at
puberty, Completes meiosis I, Secondary oocyte, Continue meiosis II, Arrest Metaphase II
• Continue and
complete Meiosis
II only upon


The origin and develo­pment of the sperm cells within the male reprod­uctive organs, the testes.
- diploid sperma­tog­onium, produces two diploid interm­ediate cells called primary sperma­toc­ytes.
- Haploid sperm, only the egg and sperm cells are haploid.
Sperma­tog­enesis -> 4 haploid sperm

Polar Bodies

- Asymmetric cell divisions in Meiosis I and II
- Asymmetric partit­ioning of cellular material
- After 2 rounds of meiosis, only 1 haploid ovum vs. 4 as with sperm

A polar body is the byproduct of an oocyte meiotic division

Comparison of Mitosis and Meiosis

Mutations with Meiosis

• Inherited mutations are present in the parents, inherited from their parents, and can be passed to gametes
• But NEW sponta­neous mutations can also occur in germline cells in meiosis
• New mutations in gametes more likely to develop or accumulate with age
• Oocytes more often have chromo­somal imbalances
• Missing or extra entire chromo­somes, usually due to non-di­sju­nction
• Sperm more often have dominant single gene mutations
• “Paternal age effect”


Sister Chromatid = identical copies formed by the DNA replic­ation of a chromo­some, with both copies joined together by a common centro­mere. In Mitosis
Homologs = Two chromo­somes in a pair – normally one inherited from the mother and one from the father. In Meiosis
Haploid = the presence of a single set of chromo­somes in an organism's cells (1n)
Diploid = A cell containing two copies of each chromosome (2n)
Somatic Cell = any cell of a living organism other than the reprod­uctive cells
Germline Cell = The cells that form eggs in females and sperm in males
Allele = variation of the same sequence of nucleo­tides at the same place on a long DNA molecule
Crossing Over = When two chromo­somes — one from the mother and one from the father — line up, parts of the chromosome can be switched
Ploidy = number of complete sets of chromo­somes in a cell
Reduct­ional division = The first cell division in meiosis, the process by which germ cells are formed, MEIOSIS
Equational division = the process of cell division wherein the chromo­somes replicate and get equally distri­buted into two daughter cells, MITOSIS

Steps of Meiosis

Meiosis = Reduct­ional division
Goal of Meiosis: produce gametes, the sperm and eggs, with half of the genetic complement of the parent cells.
Prophase 1: replicated chromo­somes condense, homologous chromsomes pair up, crossing over occurs between homologous chromo­somes, the spindle is formed, and the nuclear envelope breaks apart into vesicles
Metaphase 1: chromo­somes condense and move together, aligning in the center of the dividing cell.
Anaphase 1: Homologous chromo­somes are pulled to opposite poles of the cell but sister chromatids remain joined at their centro­meres
Telophase 1: the chromo­somes are enclosed in nuclei, four haploid daughter cells, generates genetic diversity

Meiosis 2

Prophase 2: chromo­somes condense, and a new set of spindle fibers forms. NO crossing over
Metaphase 2: INDIVIDUAL centro­meres of the paired chromatids align along the equatorial plate in both cells
Anaphase 2: Sister chromatids SEGREGATE from each other and migrate to opposite ends of the cell
Telophase 2: cell division begins again in each of the two daughter cells, creating 4 daughter cells
Mitosis = Equational division

Difference of Meiosis 1 and Meiosis 2

The goal of meiosis I is to separate homologous chromo­somes. The goal of meiosis II is to separate sister chromatids


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