Download Cell Division Meiosis

Meiosis &
Sexual
Reproduction
Heredity
Transfer of
characteristics
from parent to
offspring through
their genes
• Genome- Complete genetic
material of an organism.
• Chromosome- carry genes.
• Gene– “unit of heredity”
made of DNA.
Chromosomes & Genes
• Cellular DNA is
organized in
chromosomes.
• Genes have specific
places on
chromosomes.
Homologues
Chromosomes exist in homologous pairs in
diploid (2n) cells.
Exception: Sex chromosomes (X, Y).
Other chromosomes, known as autosomes, have
homologues.
Karyotype
A karyotype is
the complete set of all
chromosomes of a cell of
any living organism.
• Upper right is a typical
karyotype of a human male.
• Lower right is a karyotype
of a human sperm.
Sexual Reproduction
• Fusion of two gametes to
produce a single zygote.
• Introduces greater
genetic variation, allows
genetic recombination.
• With exception of selffertilizing organisms,
zygote has gametes from
two different parents.
Peter + Lois = Stewie
In humans …
• At fertilization, 23 chromosomes are donated
by each parent.
(total = 46 or 23 pairs).
• Gametes (sperm/egg):
– Contain 22 autosomes and 1 sex chromosome.
– Are haploid (haploid number “n” = 23 in humans).
• Fertilization results in diploid zygote.
– Diploid cell; 2n = 46. (n = 23 in humans)
• Most cells in the body are produced by mitosis.
• Only gametes are produced by meiosis.
Mitosis
vs.
Meiosis
• 2n
• 1n
• Clone
• Daughter cells
different from
parent cell and
from each other.
• Same genetic
information in parent
cell and daughter cell.
• Give me another one
just like the other one!
• Daughter cells have
½ the number of
chromosomes as
somatic cell.
• Shuffling the genes
(Mix it up!)
Meiosis - Sex Cell (Gamete) Formation
In meiosis,
there are 2 divisions
of the nucleus:
meiosis I
&
meiosis II
Meiosis
Animations:
http://www.sumanasinc.com/webcontent/animations/content/meiosis.html
http://www.johnkyrk.com/meiosis.html
Meiosis
Animations:
http://www.sumanasinc.com/webcontent/animations/content/meiosis.html
http://www.johnkyrk.com/meiosis.html
Mitosis vs. Meiosis
Meiosis creates genetic variation
Mitosis
• During normal cell growth, mitosis produces daughter cells
identical to parent cell (2n to 2n)
Meiosis
• Results in genetic variation by shuffling of maternal and
paternal chromosomes.
• No daughter cells formed during meiosis are genetically
identical to either mother or father.
• During sexual reproduction, fusion of the unique haploid
gametes produces truly unique offspring.
How is this “shuffling” accomplished?
Genetic shuffling of Meiosis 1
1. Crossing over in Prophase I
2. Independent assortment in
Metaphase/Anaphase I.
Crossing Over
You will also see the terms “synapsis” & “chaisma” associated with this process.
Homologues break at identical
locations, then rejoin opposite
partners.
This creates new combinations
of genes on each chromosome.
Occurs randomly several times
on every chromosome.
Results in mixing of the genes
you inherited from your
parents.
Crossing over
Two homologous chromosomes
pair up during meiosis.
Genetic material exchanged
between non-sister chromatids.
Crossing over produces
recombinant chromosomes
(genes have recombined).
Independent Assortment
Meiosis & Sexual Life Cycle
•
Life Cycle = sequence of stages
in organisms reproductive
history; conception to
reproduction.
•
Somatic cells = any cell other
than gametes, most of the cells
in the body.
•
Gametes produced by meiosis.