Transcript AQA Biology AS Level

AQA Biology AS Level
Unit 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
Homologous chromosomes
centromere
chromatids
chromosome
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
maternal
paternal
Random assortment
in meiosis I
Random assortment
in meiosis II
or
maternal
paternal
Random assortment
in meiosis I
Random assortment
in meiosis II
Crossing over increases variation
recombinant
chromosome
chiasma
In the first division of meiosis the homologous chromosomes associate
Crossing over increases variation
B
B
b
b
G
g
G
g
B, G
B, g
b, G
b, g
All gametes have a different combination of alleles on the chromosomes
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.
metaphase
prophase
anaphase
interphase
telophase
cytoplasmic division (cytokinesis)
Stages of mitosis
M
I
T
O
S
I
S
interphase
Chromosomes appear, nucleus disappears
prophase
Chromatids pulled to poles
metaphase
Chromosomes invisible; DNA replicates
anaphase
Cytoplasmic division
telophase
Chromosomes at equator, spindle forms
cytokinesis
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 cell
Duplication of organelles
other than nucleus
nuclear division
S:
anaphase
Replication of DNA
G2: Cell checks
DNA and makes any
repairs. Cell prepares
for division
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.