AQA Biology AS LevelUnit 2

Meiosis, Mitosis and the Cell Cycle

Outcomes:

• Know that cell division by meiosis results in the formation of gametes.

• Can describe the importance of meiosis in creating variation by independent assortment of chromosomes and crossing over.

• Know that cell division by mitosis results in an increase in number of identical cells for growth and repair.

• Identify and name the stages of mitosis in diagrams and photomicrographs.

• Describe the cell cycle and relate it to an understanding of cancer and its treatment.

Replication of chromosomes occurs prior to division

chromatids

centromere

chromosome

Homologous chromosomes

Meiosis consists of two divisions

Meiosis 1 Meiosis 2

Gametes are formed by meiosis:

Homologous chromosomes associate

Outcomes:

• Know that cell division by meiosis results in the formation of gametes.

• Describe the importance of meiosis in creating variation by independent assortment of chromosomes and crossing over.

• Know that cell division by mitosis results in an increase in number of identical cells for growth and repair.

• Identify and name the stages of mitosis in diagrams and photomicrographs.

• Describe the cell cycle and relate it to an understanding of cancer and its treatment.

Independent segregation increases variation

Random assortment in meiosis I

Random assortment in meiosis II

maternal paternal

or

Random assortment in meiosis I

Random assortment in meiosis II

maternal paternal

Crossing over increases variation

In the first division of meiosis the homologous chromosomes associate

chiasma

recombinant chromosome

Crossing over increases variation

All gametes have a different combination of alleles on the chromosomes

B

G

b

G

b

g

B

g

B, G B, g b, G b, g

Outcomes:

• Know that cell division by meiosis results in the formation of gametes.

• Can describe the importance of meiosis in creating variation by independent assortment of chromosomes and crossing over.

• Know that cell division by mitosis results in an increase in number of identical cells for growth and repair.

• Identify and name the stages of mitosis in diagrams and photomicrographs.

• Describe the cell cycle and relate it to an understanding of cancer and its treatment.

Mitosis produces two identical daughter cells.

prophase

metaphase

anaphase

telophase

cytoplasmic division (cytokinesis)

interphase

Stages of mitosis

MITOSIS

interphase

prophase

metaphase

anaphase

telophase

cytokinesis

Chromosomes invisible; DNA replicates

Chromosomes appear, nucleus disappears

Chromatids pulled to poles

Cytoplasmic division

Chromosomes at equator, spindle forms

Chromatids at poles, nucleus reforms

Outcomes:

• Know that cell division by meiosis results in the formation of gametes.

• Can describe the importance of meiosis in creating variation by independent assortment of chromosomes and crossing over.

• Know that cell division by mitosis results in an increase in number of identical cells for growth and repair.

• Identify and name the stages of mitosis in diagrams and photomicrographs.

• Describe the cell cycle and relate it to an understanding of cancer and its treatment.

The cell cycle

interphase

G1:Growth of daughter cellDuplication of organelles other than nucleus

S:Replication of DNA

G2: Cell checks DNA and makes any repairs. Cell prepares for division

cytoplasmic division

nuclear divisionprophasemetaphaseanaphasetelophase

Cancer

Summary• Meoisis produces haploid gametes that are genetically different.

Variation is further increased by independent segregation of chromosomes and crossing over forming recombinant chromosomes.

• Mitosis is the nuclear division which produces 2 genetically identical, diploid cells. It consists of prophase, metaphase, anaphase and telophase.

• Cell cycle consists of interphase, nuclear division (mitosis or meiosis) and cytplasmic division (cytokinesis).

• Cancer is caused by mutation of genes that regulate the cell cycle and treatment is designed to inhibit cell division.