Mitosis and Meiosis

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Cell division
• The human body is made up of trillions of cells…

Mitosis and Meiosis

• …But started with one

Understanding Cell Division
• What instructions are necessary for inheritance? • How are those instructions duplicated for distribution into daughter cells? • By what mechanisms are instructions parceled out to daughter cells?

• Parental cells produce a new generation of cells or multicelled individuals like themselves • Parents must provide daughter cells with hereditary instructions, encoded in DNA, and enough metabolic machinery to start up their own operation

The roles of mitosis

• A DNA molecule & attached proteins • Duplicated in preparation for mitosis



Chromosomal Organization

A chromosomes is DNA associated with proteins. The entire complex is tightly wound and compressed into a discrete, linear structure.

The Cell Cycle
• • • • •

Usually longest part of the cycle Cell increases in mass Number of cytoplasmic components doubles G1, S, and G2 phases Chromosomes duplicate in S phase of interphase

Chromosome Duplication a One chromosome (unduplicated)

Duplication allows a whole copy of the genome to reside in each daughter cell

one chromatid one chromatid b One chromosome (duplicated)

two sister chromatids

Each duplicated chromosome will split. One sister chromatid will be in each new daughter cell



Chromosome Number
• Sum total of chromosomes in a cell • Somatic (body) cells
– Chromosome number is diploid (2n) – Two of each type of chromosome

Human Chromosome Number
• Diploid chromosome number (n) = 46 • Two sets of 23 chromosomes each

• Gametes (Sex cells)
– Chromosome number is haploid (n) – One of each chromosome type

• Mitosis produces cells with 46 chromosomes-two of each type • X and Y chromosomes…...

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