Download Meiosis - Groby Bio Page

Starter – recap from GCSE
List the differences between
meiosis
and
mitosis?
This may help!
Mitosis
Daughter cells are genetically
identical
2 daughter cells produced
Daughter cells are diploid
One division
Normal body cells form
Occurs in all areas of the body
Produces genetic clones
Meiosis
Answers
Mitosis
Meiosis
Daughter cells are genetically
identical
Daughter cells are genetically
different
2 daughter cells produced
Four daughter cells produced
Daughter cells are diploid
Daughter cells are haploid
One division
Two divisions
Normal body cells form
Gametes/Sex Cells form
Occurs in all areas of the body
Occurs in reproductive organs
Produces genetic clones
Produces genetic variation in
cells
Meiosis
Learning objectives
 Understand the process and
purpose of meiosis
 Explain how meiosis can lead
to genetic variation
Success criteria
 Describe, with the aid of diagrams
and photographs, the behaviour of
chromosomes during meiosis, and
the associated behaviour of the
nuclear envelope, cell membrane
and centrioles. (Names of the
main stages are expected, but not
the subdivisions of prophase)
 Explain the terms allele, locus and
crossing-over
 Explain how meiosis and
fertilisation can lead to variation
through the independent
assortment of alleles
Diploid and Haploid
 Normal body cells have the normal number of chromosomes
46
You might see this
explained elsewhere as ‘2n’.
We call these cells DIPLOID. It means that each body cell contains
two of each chromosome – one from mum and one from dad.
 Gametes though, have half the normal number of chromosomes
And this might be
explained as just ‘n’.
23
We call these cells HAPLOID. There’s only one copy of each
chromosome.
At fertilisation, a haploid sperm will fuse with a haploid egg.... which
makes a cell with the normal, diploid number of chromosomes 
Key definitions
 Meiosis – this is a reduction division resulting in the
daughter chromosomes having half the original
number of chromosomes. They are haploid.
 Allele – a version of a gene
 Locus – the position of a gene on a chromosome
Key Terms: Put on as many labels
as you know
Key Terms: Answers
Sister Chromatids
Bivalents/
Homologous
Pairs
Chromatid
Centromere
Gene
Gene
Meiosis
 Review the notes you made in preparation for this
lesson on the processes in meiosis as we whiz through
the next powerpoint and animation
 Meiosis whiz thru
 Meiosis animation
Micrographs: Put in order and
name that stage!
Stages: Answers
Prophase I
Metaphase II
Metaphase I
Anaphase II
Anaphase I
Telophase II
Telophase I
Genetic variation
 Crossing over – lengths of DNA are swapped form one
chromosome to another
 Genetic reassortment (independent assortment/segregation)
 Of chromosomes - Random distribution of maternal and paternal
chromosomes at metaphase 1
 Of chromatids – Random distribution of sister chromatids at
metaphase 11
 Fertilisation – any egg can fuse with any sperm
 Mutation – may occur during interphase when DNA
replicates
Plenary – part 1
Event
Division
I or II
1. The chromosomes, each in the form of a pair
of chromatids, have arrived at the poles of the
spindle and have started to uncoil.
2. Homologous chromosomes form bivalents
with chiasmata.
3. Sister chromatids move towards opposite
poles of the spindle.
4. Pairs of homologous chromosomes line up at
the equator of the spindle.
I
Phase
(anaphase, metaphase,
prophase or telophase)
Telophase
I
Prophase
II
Anaphase
I
Metaphase
Plenary - part 2
The diagram shows a cell undergoing cell division.
Identify the type and stage of cell
division shown. Give evidence from the
diagram to support your answer. (3)
(meiosis) anaphase I;
chromosomes are moving apart;
chromosomes still double structures;
Homework
In preparation for the next lesson write definitions for
the following words:
Gene
Linkage
Dominant
Homozygous
Haploid
Allele
Phenotype
Recessive
Heterozygous
Diploid
Locus
Genotype
Codominant
Differences between mitosis and meiosis
MITOSIS
MEIOSIS
One division
Two divisions
The number of chromosomes
remains the same
The number of chromosomes
is halved
Homologous chromosomes
do not pair up
Homologous chromosomes
pair up to form bivalents
Chiasmata do not form and
crossing over never occurs
Chiasmata form and
crossing over occurs
Daughter cells are
genetically identical
Daughter cells are genetically
different from parent cells
Two daughter cells are formed Four daughter cells are formed