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!