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BIOLOGY Ch 6 - Chromosomes and Cell reproduction
Cell division –
DNA Reproduction:
Asexual –
Sexual –
Prokaryotic cell reproduction –
e.g. BINARY FISSION –
Eukaryotic cell reproduction –
Gene –
Chromosome ChromatidsCentromereDraw Figure _____
Types of cells:
 Somatic cells- body cells e.g. ____________________

Sex cells – reproductive cells e.g. _________________
Somatic cells - have 23 pairs of chromosomes – each has 2 homologous
chromosomes (similar in size, shape and genetic content)
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Cells are also either:
Diploid ( ) –
e.g.
OR
Haploid ( ) –
e.g.
Chromosome number – constant within a species
Does an increase in size lead to increase in the number of chromosomes?
Types of chromosomes
Change in chromosome number:
TRISOMYe.g.
Karyotype –
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Change in chromosome structure – MUTATIONS
There are 4 types:
Draw the ORIGINAL CHROMOSOME here:
Then draw and show the following mutations:
DELETION- piece of chromosome breaks off
DUPLICATION- 2 copies of certain gene carried
INVERSION- chromosome piece attaches to original chromosome in reverse orientation
TRANSLOCATION- a piece attaches to a non homologous chromosome
EUKARYOTIC LIFE CYCLE
 Repeating sequence of cellular growth and division during life of an organism
 It has 5 stages
 Spends 90% of time in stage-1(Interphase)
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1) First growth phase G1 – major phase – cells grow rapidly, carries out routine
functions
2) Synthesis phase S – the cells’ DNA is copied
3) Second growth phase G2 – prepares for nucleus to divide, microtubules(protein
fibers) arranged
4) Mitosis – Nucleus divides into two, same number and type of chromosomes
5) Cytokinesis – division of the cytoplasm
Control of cell cycle:
 Cell growth check point – decides if cell will divide
(Nerve and muscle cells never divide)

G2 check point – DNA replication checked by repair enzymes

Mitosis – triggers exit from mitosis
What happens if cell control is lost???
___________________
It is the uncontrolled growth of cells!
Mitosis and Cytokinesis
Spindles
During mitosis, the chromatids on each chromosome are moved to the opposite side of
the dividing cell with the help of the spindle
Formation of spindle
Each cell has 1 pair of centriole at right angles to each other. During G2 phase, 2 pairs are
formed and they separate to move to opposite ends and spindles are formed
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MITOSIS
It has 4 stages
1) Prophase
2) Metaphase
3) Anaphase
4) Telophase
CYTOKINESIS
CELL CYCLE REGULATORS
Internal –
e.g.
External e.g
Cyclins –
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