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Meiosis Meiosis Chapter 10.2-3Chapter 10.2-3
Produces
* FOUR sex cells
* each has
HALF the number of chromosomes
of the parent’s cell
(2 mitosis cycles in a row)
Why must Why must sex cells sex cells
(gametes) (gametes) have HALF have HALF the number the number
of of chromosomchromosom
es of a es of a normal cell?normal cell?
Normal cells have
two sets of chromosomes,
one from each parent
So each sex cell can have only one set,
which is half the number of a normal cell.
MeiosisMeiosis process which produces process which produces gametesgametes which which
contain contain half the number of chromosomeshalf the number of chromosomes as the parent’s body cellsas the parent’s body cells
4 4 spermsperm
1 1 eggegg andand 3 3 polar bodiespolar bodies
gametesgametes
How many male gametes are produced?
How many female gametes are produced?
Egg
DiDiploploidid
A normal cell with A normal cell with
twotwo sets of chromosomes sets of chromosomes
– – one from each parentone from each parent
2n2n Body Body cellcell
somatsomatic cellic cell
An illustration of an organisms chromosomes is called a karyotype.
This illustration shows human chromosomes next to chimpanzee chromosomes. We have 46, they have 48. Look at chromosome 2.
How similar are human and How similar are human and chimpanzee chromosomes?chimpanzee chromosomes?
Very similar!
A cell with A cell with one set of chromosomesone set of chromosomes, , halfhalf of the normal amount of the normal amount
HaHaploiploidd nn
sex sex cellcell
gametgametee
HomoHomologous logous chromosomeschromosomes
A matching pair of A matching pair of samesame chromosome, chromosome, oneone from each parentfrom each parent
– – each chromosome has genes for the each chromosome has genes for the samesame traitstraits
spermsperm
Male Male gametegamete, a haploid sex cell (n), a haploid sex cell (n)
Egg Egg
Female Female gametegamete, a haploid sex cell (n), a haploid sex cell (n)
Sexual reproductionSexual reproduction
Involves the Involves the productionproduction (meiosis) (meiosis)
and and fusionfusion (fertilization) (fertilization)
of of haploid gameteshaploid gametes (sperm and (sperm and egg)egg)
Meiosis phase 1Meiosis phase 1(pg 268)(pg 268)
Process that produces 2 haploid cells Process that produces 2 haploid cells which are which are NOTNOT identicalidentical
– – both cells have only both cells have only
one of each of a cell’s homologous pairs one of each of a cell’s homologous pairs
(already (already DOUBLEDDOUBLED and has cross-overs) and has cross-overs)
Crossing overCrossing over
When When sectionssections of of homologous homologous chromosomeschromosomes cross overcross over each each other and genes other and genes are are traded or traded or switchedswitched
Meiosis phase 2 Meiosis phase 2
Process that produces 4 haploid cells Process that produces 4 haploid cells – – none of which are identical none of which are identical – – each has each has oneone of each original homologous pair of each original homologous pair
(with cross overs)(with cross overs)
Meiosis phase 1 and 2 Meiosis phase 1 and 2
Process that produces 4 haploid cells Process that produces 4 haploid cells – – none of which are identical none of which are identical – – each has each has oneone of each original homologous pair of each original homologous pair
(with cross overs)(with cross overs)
Genetic recombinationGenetic recombination
Increases differences among Increases differences among offspring – caused by meiosis and offspring – caused by meiosis and
- increased by the crossing over of - increased by the crossing over of chromosomeschromosomes
Sister chromatidsSister chromatids
identical copiesidentical copies of a chromosome of a chromosome connected by a connected by a centromerecentromere
NonNondisjunctdisjunctionion
The The failurefailure of of homologous homologous chromosomes chromosomes to to separateseparate and go and go to different cells to different cells during meiosis, during meiosis, resulting in resulting in gametes that gametes that have an have an abnormal abnormal number of number of chromosomeschromosomes
Polyploidy Polyploidy
the condition of the condition of having three, four, having three, four, or more or more sets of sets of chromosomeschromosomes instead of the two instead of the two normally present normally present in diploidsin diploids
many normal number of chromosomes
spermatogenesisspermatogenesis
Process in which Process in which 4 haploid sperm4 haploid sperm are are producedproduced
creation
oogenesisoogenesis
Process in which Process in which 1 haploid egg1 haploid egg and and 3 3 polar bodiespolar bodies are produced are produced
polar bodiespolar bodies
Three of the Three of the haploid cellshaploid cells produced produced in oogenesis, in oogenesis,
they cannot be fertilized by spermthey cannot be fertilized by sperm
And now a quiz…And now a quiz… What’s the difference between mitosis and meiosis?What’s the difference between mitosis and meiosis? Mitosis produces Mitosis produces Meiosis produces Meiosis produces
in in phasesphases
twotwo
twotwo identical identical diploid diploid nucleinucleiin body in body cellscells
four four different different
haploid haploid
gametesgametes
This illustration does not show that chromosomes cross over, which would make each gamete
unique.
Mahalo!Mahalo!