Meiosis

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Slide 1

Meiosis

Cell division – ‘reduction division’

Production of sex cells – gametes

Meiosis errors

Slide 2

Why do we need meiosis?

Meiosis is necessary to halve the number of chromosomes going into the sex cells

Why halve the chromosomes in gametes?

At fertilisation the male and female sex cells will provide ½ of the chromosomes each – so the offspring has genes from both parents

Slide 3

Slide 4

Meiosis

Parent cell – chromosome pair

Chromosomes copied

1st division - pairs split

2nd division – produces 4 gamete cells with ½ the original no. of chromosomes

Slide 5

Meiosis – mouse testes

Parent cell

4 gametes

1st division

2nd division

Slide 6

Meiosis – division error

Chromosome pair

Slide 7

Meiosis error - fertilisation

Should the gamete with the chromosome pair be fertilised then the offspring will not be ‘normal’.

In humans this often occurs with the 21st pair – producing a child with Downs Syndrome

Slide 8

21 trisomy – Downs Syndrome

Can you see the extra 21st chromosome?

Is this person male or female?