Mitosis: Cell Division

New cells are produced: for growth to replace damaged or old cells For asexual reproduction in some organisms

Interphase – cell copies DNA and prepares for division Cell Division - process by which a cell splits into two identical daughter cells *Occurs in two main phases:  Interphase – cell copies DNA and prepares for division Mitosis – chromosomes separate into two new cells

What are chromosomes? DNA containing cell’s genetic code Each chromosome has a matching pair (homologous) During interphase, each chromosome copies itself

Life Cycle of the Cell Mitosis = nuclear division Mitosis is followed by cytokinesis (cell division) The steps of mitosis ensure that each new cell has the exact same number of chromosomes as the original Interphase = growth phase, differentiation occurs

DNA Replication DNA must be copied before cell division Each new cell will then have an identical copy of the DNA Happens during the S (synthesis) phase of cell cycle

The Cell Cycle Interphase (longest phase) G1 - first growth (gap) phase Synthesis - DNA makes a copy G2 - second growth (gap) phase, preparing for mitosis Mitosis - nucleus divides, ensuring each new cell has the exact number of chromosomes as parent

Uncontrolled Cell Division If the cell cycle is not controlled, cell division does not stop and forms tumors. Cancer is uncontrolled cell division Cancer cells

Uncontrolled Cell Division Cancer cells do not carry out necessary functions.

One chromosome comes from the mother, the other comes from the father. Definitions Homologous chromosomes a pair of chromosomes that are similar and carry genes for the same traits One chromosome comes from the mother, the other comes from the father.

Diploid vs. Haploid diploid (2n) cells have a full set of chromosomes - pairs of homologous chromosomes. haploid (n) cells are Sex cells or gametes and have ½ the diploid number of chromosomes - one chromosome from each homologous pair.

MITOSIS Mitosis is Cell division that begins with 1 diploid cell and ends with 2 diploid cells Asexual reproduction

Interphase • Prophase • Metaphase • Anaphase • Telophase IPMAT

1. chromosomes visible (chromatids) 2. centrioles migrate to the poles 3. nuclear membrane disappears 4. spindle forms

1. chromosomes line up on the equator, spindle attaches

1. chromatids separate and move to opposite poles

1. chromosomes unwind 2. nuclear membrane reforms 3. spindle disappears

- division of the cytoplasm to form 2 new daughter cells - organelles are divided - daughter cells are genetically identical Cells return to interphase

Name the phases starting at the top.

Name the phase Identify X Identify Y

5. Name the phase

6. Name the phase

Meiosis is the formation of gametes or sex cells (egg and sperm) Meiosis II Diploid Haploid

Meiosis Forms Haploid Gametes Meiosis is cell division that reduces the number of chromosomes. from mom from dad child too much! meiosis reduces genetic content The right number!

It begins with one diploid cell and ends with 4 haploid cells. Meiosis It begins with one diploid cell and ends with 4 haploid cells. Meiosis is part of sexual reproduction. Fertilization is when two haploid gametes join to form a diploid zygote.

Crossing-Over Homologous chromosomes cross over each other in meiosis Pieces of chromosomes or genes are exchanged Produces Genetic variation in the offspring

Karyotype A picture of chromosomes arranged in pairs First 22 pairs are called autosomes Last pair are the sex chromosomes XX female or XY male

The Y Chromosome Decides Boy or Girl? The Y Chromosome Decides Y - Chromosome X - Chromosome

Comparing Mitosis and Meiosis

Comparison of Mitosis and Meiosis REPRODUCTION TYPE PURPOSE # CELLS START # CELLS END CHROMOSOMES START (haploid/diploid) CHROMOSOMES END (haploid/diploid) sexual asexual Grow, repair, reproduction (in some organisms) Produce gametes 1 1 4 2 diploid diploid diploid haploid

Phases of mitosis

Asexual & Sexual Reproduction CELL DIVISION Process Advantages Genetic Variation mitosis meiosis Produces haploid gametes that join to form a diploid zygote Produces identical diploid cells Not identical to parent Un-wanted traits might not be passed on Needed traits for adaptation are passed on Good in changing conditions Identical cells are produced Only one parent good in unchanging conditions No Yes

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