12DA Biology
Cell Division and Genetics
UNIT 5
Unit 5 REVISION NOTES: Cell Division and Genetics
Mitosis
Meiosis
2 daughter cells
4 daughter cells
identical to parent
Different
Diploid
Haploid
Repair cells
Produce gametes (sex cells)
HIGHER TIER ONLY
This process of MEIosis, causes each gamete to be different, because every time the
cell divides, a different mixture of chromosomes occurs. This is called INDEPENDENT
ASSORTMENT. This mixing up is what results in brothers and sisters being similar or
different.
FOUNDATION AND HIGHER TIER
Keywords
Phenotype – the characteristics you see.
Genotype – written notation of the genes present.
Here is the karyotype of these 2 individuals.
At pair 23
the lady has 2 X chromosomes.
the man has 1 X and 1 Y chromosome.
Dominant – this gene is in charge (it’s the boss!) we know the dominant gene because
it is a CAPITAL LETTER
12DA Biology
Cell Division and Genetics
UNIT 5
Recessive – this gene is “bullied” by the dominant one. We know this gene because it
has a little letter.
Homozygous – is when the two genes are the same. E.g. TT or tt or FF or gg.
Heterozygous – is when the two genes are different. E.g. Tt or Gg or Ff or Pp.
Punnett Squares – be able to complete the punnett squares – be able to work out
either the % of each phenotype or the ratio between the 2 phenotypes.
B
B
b
b
HIGHER TIER ONLY
Backcrosses.
These are used to work out if the individual displaying the Dominant characteristic is
Heterozygous (Tt) or Homozygous (TT).
HOW?
We do 2 Punnett Squares crossing both of the above traits with Homozygous recessive (tt)
If the parent is TT
T
All offspring will show the
t
DOMINANT Characteristic.
t
T
If the parent is Tt
50% will show the DOMINANT
T
characteristic and 50% will show the
t
RECESSIVE characteristic.
t
HIGHER TIER ONLY
Asexual Reproduction in plants produces CLONES.
Clones are Genetically identical offspring.
t
12DA Biology
Cell Division and Genetics
UNIT 5
Gardeners can create these clones through the process of Tissue Culture.
1. Chose a plant with desirable characteristics.
2. Use a sterile scalpel to cut a section of stem.
3. Place the explants into nutrient jelly to promote growth.
4. Explants grow into small plants, then plant out.
Market gardeners use this process as it is a faster way of producing plants for sale.