Please get

4 pipe cleaners

in 4 different colors

One pair are partnersThe other pair are partners

Cell DivisionCell Division

Cell DivisionCell Division• 2 types:2 types:• MitosisMitosis –– 1 body cell divides to 1 body cell divides to

make 2 genetically identical body make 2 genetically identical body cellscells

Cell DivisionCell Division• MeiosisMeiosis –– 1 germ cell (in testes or 1 germ cell (in testes or

ovaries) divides twice to make 4 ovaries) divides twice to make 4 genetically different sex cellsgenetically different sex cells

• Sex cells = Sex cells = gametesgametes; sperm and ; sperm and ova ova

Quick CheckQuick Check• A lily produces pollen that can A lily produces pollen that can

fertilize the ovule of another lily to fertilize the ovule of another lily to make new lily plantsmake new lily plants

• What kind of cell division is this? What kind of cell division is this?

Quick CheckQuick Check• Marcus got a paper cut in 1Marcus got a paper cut in 1stst period period• By 5By 5thth period he noticed that the period he noticed that the

wound had started to heal.wound had started to heal.• What kind of cell division is this? What kind of cell division is this?

Homologous chromosomesHomologous chromosomes• Each person has 2 of every Each person has 2 of every

chromosome chromosome – 1 from mom1 from mom– 1 from dad1 from dad

• Together they are called Together they are called homologous chromosomeshomologous chromosomes– Same genes on themSame genes on them

MeiosisMeiosis• Produces genetic diversityProduces genetic diversity

https://www.youtube.com/watch?v=JIUK2KSbvvI&t=22s

Key events in MeiosisKey events in Meiosis1.1. Homologous chromosomes Homologous chromosomes

cross over each other and cross over each other and swap piecesswap pieces

Key events in MeiosisKey events in Meiosis2. Homologous chromosomes 2. Homologous chromosomes pair up pair up –– then separate to go to then separate to go to different cellsdifferent cells

Key events in MeiosisKey events in Meiosis3. Each cell at the end of 3. Each cell at the end of meiosis contains only ½ the meiosis contains only ½ the normal number of normal number of chromosomes and each cell is chromosomes and each cell is genetically uniquegenetically unique

Pipe Cleaner Chromosome Practice

Directions

Cut each pipe cleaner in ½ Which two colors are going to be

homologues?Remember: homologous chromosomes are

partner chromosomes – not identical but nearly so.

One chromosome, that shows that the DNA has been copied already.

A homologous pair of chromosomes

One sister chromatid

Centromere on a chromosome

4 chromosomes after the DNA has been copied

Step 1 of meiosis

Crossing over between homologous chromosomes occurs

Model it by cutting your chromosomes

Let’s Practice with our pipe cleaners!

Set up Prophase 1 This is when crossing over will happenCarefully cut off the end of one chromosome

and attach it to its homologous pair

Step 2 of Meiosis

Homologous chromosomes pair up in the middle of the cell

Stage 3 of meiosis

Homologous chromosomes move to opposite ends of the cell

Stage 4 of Meiosis

2 different cells

2 different cells

2 different cells

4 different cells

Sexual ReproductionSexual Reproduction• Sex cells divide by meiosisSex cells divide by meiosis to to

produce produce haploid (n) haploid (n) gametesgametes

Sexual ReproductionSexual Reproduction• Gametes will join & fertilizeGametes will join & fertilize

• Two gametes join to form aTwo gametes join to form a zygote zygote

SpermatogenesisSpermatogenesis• Takes 8-9 weeks to completeTakes 8-9 weeks to complete

Sperm FormationSperm Formation

• A sperm is not a sperm UNTIL….A sperm is not a sperm UNTIL….– It has a full flagellaIt has a full flagella– Is motile (can move)Is motile (can move)

OogenesisOogenesis

Model with pipe cleanersModel with pipe cleaners• Partner A: show the germ cell, diploid Partner A: show the germ cell, diploid

number 4 in the first stage of meiosisnumber 4 in the first stage of meiosis

• Partner B: show the 4 haploid cells (2 Partner B: show the 4 haploid cells (2 chromosomes) at the end of meiosischromosomes) at the end of meiosis

Evolution of SexEvolution of Sex• From From asexualasexual ---> --->

sexualsexual• From external From external

fertilization ---> internal fertilization ---> internal fertilizationfertilization

• Simplest = “broadcast Simplest = “broadcast fertilization,” eggs and fertilization,” eggs and sperm sent into the sperm sent into the water, chance meetingwater, chance meeting

Evolution of SexEvolution of Sex• Evolved to sperm released, Evolved to sperm released,

swim to female, enter and swim to female, enter and fertilize; larva is released into fertilize; larva is released into waterwater

• To eggs and sperm released To eggs and sperm released externally but right next to externally but right next to each other (in a nest)each other (in a nest)

• To internal fertilization, To internal fertilization, fertilized egg released into fertilized egg released into water (oviparous)water (oviparous)

Evolution of SexEvolution of Sex• To internal fertilization, eggs To internal fertilization, eggs

hatch inside, juvenile hatch inside, juvenile released into water released into water (ovoviviparous)(ovoviviparous)

• Some newly-hatched sharks Some newly-hatched sharks eat their unhatched siblings eat their unhatched siblings in the womb: in the womb: “intrauterine “intrauterine cannibalism”cannibalism”

• To internal fertilization, live To internal fertilization, live birth (viviparous)birth (viviparous)

Evolution of SexEvolution of Sex• Marsupials = born undeveloped (as Marsupials = born undeveloped (as

embryos), crawl into a pouch to embryos), crawl into a pouch to complete developmentcomplete development

• Placental mammals = held full-term Placental mammals = held full-term within the uterus.within the uterus.

• From no care of young ----> From no care of young ----> increased parental careincreased parental care

• From eggs ----> placenta (embryo From eggs ----> placenta (embryo more protected in mother)more protected in mother)

Meiosis Meiosis II

Prophase IProphase I• DNA replication has DNA replication has

already occurredalready occurred• Homologous Homologous

chromosomes chromosomes pairpair and form and form tetradstetrads, , joined at a joined at a chiasmatachiasmata

DNA Wrapping Around DNA Wrapping Around Proteins to Condense Into Proteins to Condense Into

ChromosomesChromosomes

tetradstetrads cross cross over and over and separate into separate into individual individual chromosomeschromosomes

TetradTetrad

Prophase IProphase IEach tetradEach tetradhas twohas twochromo-chromo-somes &somes &fourfourchromatidschromatids

Metaphase IMetaphase I• Tetrads Tetrads line upline up at metaphase plate. at metaphase plate.• Orientation is Orientation is randomrandom• 50-50 chance50-50 chance for for

daughter cells to get daughter cells to get either mother's or either mother's or father's homologue father's homologue

Anaphase IAnaphase I• Chiasmata Chiasmata separateseparate..• Chromosomes moveChromosomes move to separate poles to separate poles• Daughter cells now Daughter cells now

haploid (haploid (2323 chromosomes), but chromosomes), but each chromosome each chromosome has has two chromatidstwo chromatids. .

Crossed over X-shaped chromosomes

Telophase ITelophase I• Nuclear envelopes may Nuclear envelopes may reformreform, or the cell , or the cell

may quickly start meiosis IImay quickly start meiosis II

• CytokinesisCytokinesis– Analogous to mitosisAnalogous to mitosis

where two complete where two complete daughter cells form. daughter cells form.

Meiosis I ReviewMeiosis I Review

Meiosis IIMeiosis II• Similar to mitosis: Similar to mitosis: no "S" phaseno "S" phase..

Meiosis IIMeiosis II• Chromatids Chromatids no longer identicalno longer identical

• Meiosis II separates chromatids Meiosis II separates chromatids producing producing two daughter cellstwo daughter cells each each with with 2323 chromosomes (haploid.) chromosomes (haploid.)

Comparing Meiosis & MitosisComparing Meiosis & MitosisMitosisMitosis

• Homologous Homologous chromosomes chromosomes independent of independent of each othereach other

• identicalidentical daughter daughter cellscells

Meiosis Meiosis • Homologous Homologous

chromosomes chromosomes pair,pair, forming tetrads until forming tetrads until anaphase Ianaphase I

• daughter cells daughter cells haploid, uniquehaploid, unique

Comparing Meiosis & MitosisComparing Meiosis & MitosisGenetic identity of progenyGenetic identity of progenyMitosisMitosis

• IdenticalIdentical daughter cells daughter cells

Meiosis Meiosis • Daughter cells have Daughter cells have

new assortment of new assortment of parental chromosomesparental chromosomes

• Chromatids Chromatids not not identical; crossing identical; crossing overover

Meiosis ReviewMeiosis ReviewWhat stage is this?How can you tell?

A B

Meiosis ReviewMeiosis ReviewWhat stage is this?How can you tell?

A B

Meiosis ReviewMeiosis ReviewWhat stage is this?How can you tell?

A B

Meiosis ReviewMeiosis ReviewWhat stage is this?How can you tell?

A B

Meiosis ReviewMeiosis ReviewWhat stage is this?How can you tell?

A B

Meiosis ReviewMeiosis ReviewWhat stage is this?How can you tell?

A B