Look at this picture carefully.

Q1. What does this picture

show?

Q2. Where would you find these?

Q3. Why is there two of each

number?

Look at this picture carefully.

Q1. What does this picture

show?

Q2. Where would you find these?

Q3. Why is there two of each

number?

Chromosomes

In the Nucleus

1 from each parent

Genetic Information

Nucleus

Keywords: Chromosomes, Nucleus, Asexual reproduction,

Inside the Nucleus

Chromosomes

Keywords: Chromosomes, Nucleus, Asexual reproduction,

Chromosomes are found in pairs

Keywords: Chromosomes, Nucleus, Asexual reproduction,

HumansHuman reproduction involves the fusing of the sperm and egg.

If both the sperm and egg were diploid numbers then we would have too many chromosomes. Then every generation after that would continue to have more and more.

Solution:

So when sperm and eggs are formed, they only have a haploid number of chromosomes.

Keywords: Chromosomes, Nucleus, Asexual reproduction,

The Process – Meiosis Key points - There are two cell divisions!

Step 1:The homologous chromosomes pair up and their chromatids wrap around each other.

Step 2:Chromatids move apart and so we form 4 cells. Each with 23 chromatids.

Keywords: Chromosomes, Nucleus, Asexual reproduction,

Keywords: Chromosomes, Nucleus, Asexual reproduction, Mitosis, Duplicate,

Meiosis.

This process forms our sex cells (gametes).

Variation Variation occurs when meiosis occurs – there is helpful as it allows organisms to adapt and survive in a changing world.

This happens by:

1.Independent segregation of homologous chromosomes.

2.Recombination of homologous chromosomes by crossing over.

Keywords: Chromosomes, Nucleus, Asexual reproduction,

Independent Segregation of Homologous Chromosomes

During stage 1 – each chromosome lines up.

Therefore there are 23 pairs lined up in the centre of the cell.

The line up though is in a random order.

One of each pair goes to the daughter cell – which one and with which one of the other pairs depends on how they are lined up.

Which alleles of the genes are passed on therefore is random and so creates new genetic combinations.

Keywords: Chromosomes, Nucleus, Asexual reproduction,

G = Green Eyesg = Grey Eyes

Y = Blood group Ay = Blood group B

What is the outcome of

each cell division?

Crossing OverStage 1 – Chromosome line up.

Not though straight forward and simple. The following can happen:

i.The chromatids of each pair become twisted around one another. This twisting can lead to bits becoming broken off. The broken bits re-join with the chromatids of its homologous partner.

Keywords: Chromosomes, Nucleus, Asexual reproduction,

Crossing OverThe chromatids cross over in many places – so known as Crossing Over.

The broken portions then recombine with another chromatid – called recombination.

Keywords: Chromosomes, Nucleus, Asexual reproduction,

Chalk or coloured pencils.

Pipe Cleaners

Coloured match sticks

Modelling clay

Keywords: Chromosomes, Nucleus, Asexual reproduction, Mitosis, Duplicate,

Quiz Time

Question 1: How many pairs of chromosomes are there in a normal human cell?A: 46B: 48C: 23D: 24

Question 2: Where are chromosomes found in a cell?

A: NucleusB: CytoplasmC: RibosomeD: Mitochondria

Question 3: Which of the following is an example of a gamete produced by Meiosis?A: Nerve cellB: Palisade cellC: OvumD: Guard cell

Question 4: Which of the following statements is true?

A: Meiosis has only 1 division B: Mitosis has 2 divisionsC: Meiosis has 2 divisionsD: Meiosis has no divisions

Question 5: Which process results in identical offspring?

A: MeiosisB: MitosisC: Meiosis and Meiosis D: No of the above

Question 6: Put the following in the correct order.A: Arms of chromosomes are pulled apartB: DNA replicatesC: Two identical cells producedD: Chromosomes line up at centre of cell.

B D A C

Are you now able to….

I still feel unsure. I need some more help to understand.

I feel ok. I need to do some more work to check my understanding.

I am happy and feel I understand and can explain the main points.

Keywords: Chromosomes, Nucleus, Asexual reproduction, Mitosis, Duplicate,