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Transcript of Meiosis+Mitosis
The Mad Scientist.
Martin spends his life looking down a microscope.
Lets see what Martin is looking at today!
Skin cells are continually lost.
To make new cells the body carries out cell division.
State why cells divide
Describe how chromosomes are involved in cell division
Explain how cells divide by mitosis and meiosis
Use keywords to correctly answer questions
How many reasons can you think of why new cells have to be made?
Cells divide where the body needs to:
Replace worn out cells
Repair damaged tissue
Create sex cells (gametes)
Chromosomes and genes
The information in
you must learn for the exam
Answer the question on the worksheet as we go through the slides
This means that all human characteristics must be something to do with chromosomes. Where are chromosomes found?
Passing on characteristics
What makes this baby human? What determines its gender?
In all living things, characteristics are passed on in the chromosomes that offspring inherit from their parents.
What do chromosomes look like?
Chromosomes are most visible
during cell division when they
replicate and look like this…
Chromosomes are long strands of genetic information
located in the nuclei of cells.
chromosomes contain many different
cat = 19 pairs
chicken = 39 pairs
maize = 10 pairs
fruit fly = 4 pairs
Other species have a different number of pairs of chromosomes; for example:
How many chromosomes?
23 pairs of chromosomes
Most human body cells contain 46 chromosomes. How many pairs of homologous chromosomes is this?
You inherit half of your chromosomes from your mother and half from your father.
Each pair of chromosomes contains
one chromosome that has been inherited from each parent
This means there are 2 sets of the same information
chromosome from male parent
chromosome from female parent
Where does each chromosomes come from?
Most cells of the body contain chromosomes in matching pairs.
What is DNA?
A gene is a small section of DNA
is a very long molecule
of tightly coiled DNA.
DNA stands for
DNA molecules carry the code that controls what cells are made of and what they do.
Chromosomes and their genes are made of a molecule
This means there is a 50% chance of babies being male or female
Male or female?
Females have XX
Males are XY
Sex chromosome from male parent = X or Y
Sex chromosome from female parent = X
One of the 23 pairs of chromosomes carries the genes that
determines which sex you are
The name for making new body cells. The new cells are genetically identical to the original cell
Two genetically identical cells are produced
Chromosome single strands move to the poles of the cell
Spindle forms. Chromosomes arranged along the equator
Each chromosome is copied (DNA replication)
Stages of mitosis
Cut out the stages of mitosis
Arrange them in the correct order
Stick them in your books with space around them
Write notes as we go through the slide again
What have you learned so far?
Remember mitosis –
cells are formed with
of chromosomes in each.
How could you change this process to create 4 new cells, each with
23 single chromosomes?
Meiosis is mitosis + 1 extra step
The new cells divide again to form gametes with half the number of chromosomes (humans = 23)
Meiosis is the name for making gametes (sex cells)
The story of meiosis..
MEIOSIS is necessary otherwise if the gametes had 23 pairs then the fertilized egg would have 2 double the number of chromosomes
46 chromosomes per cell
23 chromosomes per cell
46 chromosomes per cell
46 chromosomes per cell
True or false?
True – it is the process by which body cells divide to make new cells.
Mitosis is necessary for growth, repair and replacement of tissues.
False – in meiosis the number of chromosomes is halved. This known as reduction division.
In meiosis the number of chromosomes stays the same.
True – it also takes place in the ovaries.
Meiosis takes place in the testes.
False – mitosis involves one division of chromosomes.
Mitosis involves two divisions of chromosomes.
Mitosis results in genetically identical cells.
False – meiosis is known as reduction division.
Mitosis is known as the reduction division as the number of chromosomes is less than at the start.
and make an account for your whole group that you can all access.
Once you have made your group and given it a name, you must go to
From here click on the link
'how to make your website'
and follow the instructions.
Organise yourselves into groups of
No more no less!
House Point Harry