Wednesday, 1/16/13Wednesday, 1/16/13Turn in your HW (the article)Turn in your HW (the article)Answer the following in your notes:Answer the following in your notes:Remember: Remember: Why do cells undergo mitosis? Why do cells undergo mitosis? What is the end result of a cell What is the end result of a cell undergoing mitosis? undergoing mitosis? Think:Think: We have discussed how somatic We have discussed how somatic cells (body cells other than the cells (body cells other than the gametes – egg/sperm) are formed…gametes – egg/sperm) are formed…what process forms the sex cells (the what process forms the sex cells (the gametes-sperm/egg)?gametes-sperm/egg)?

This process is called MEIOSIS.This process is called MEIOSIS.

The BasicsThe BasicsGenes (code for things like eye color, skin Genes (code for things like eye color, skin pigmentation, hormones, etc) are located pigmentation, hormones, etc) are located on the chromosomes.on the chromosomes.Each organism must inherit one copy of Each organism must inherit one copy of every gene from both parents.every gene from both parents.Most organisms have 2 complete sets of Most organisms have 2 complete sets of genes.genes.Those two sets must be separated in Those two sets must be separated in Meiosis so that each gamete produced Meiosis so that each gamete produced contains just one set of genes.contains just one set of genes.

Chromosome #Chromosome #Humans have 46 total chromosomes.Humans have 46 total chromosomes.– 23 came from your mother23 came from your mother– 23 came from your father23 came from your father

Each pair of chromosomes are referred to as Each pair of chromosomes are referred to as homologous chromosomes homologous chromosomes (What did the root word (What did the root word homohomo mean again? mean again?

All 46 chromosomes are present in every All 46 chromosomes are present in every human body cell (a.k.a. human body cell (a.k.a. somatic cellsomatic cell).).– This is the This is the diploiddiploid chromosome number (2 sets ). chromosome number (2 sets ).

(What did the root word (What did the root word didi mean again?) mean again?)

23 pairs

GametesGametes

GametesGametes are are sex cellssex cells —sperm or egg. —sperm or egg.

Gametes contain only 1 copy of each Gametes contain only 1 copy of each chromosome.chromosome.

These cells are haploid (1 set)These cells are haploid (1 set)– sounds like “half”, so they only have half of sounds like “half”, so they only have half of

the number of chromosomesthe number of chromosomes

Humans have 23 chromosomes in every Humans have 23 chromosomes in every gametegamete. . Not 23 pairs, just 23!Not 23 pairs, just 23!

Diploid & HaploidDiploid & HaploidDiploidDiploid = a cell with = a cell with two two sets of sets of chromosomes, chromosomes, 2n2n

HaploidHaploid = a cell with = a cell with one one set of set of chromosomes, gametes, chromosomes, gametes, 1n or n1n or n

n = number of chromosomes in the n = number of chromosomes in the organism (23 in humans)organism (23 in humans)

Purpose of MeiosisPurpose of Meiosis

MeiosisMeiosis forms the gametes (sperm and eggs) forms the gametes (sperm and eggs) that are necessary for sexual reproduction.that are necessary for sexual reproduction.

Gametes need to beGametes need to be haploid haploid so that when they so that when they meet for fertilization, the zygote (fertilized egg) meet for fertilization, the zygote (fertilized egg) has 2 copies of the genetic materialhas 2 copies of the genetic material (diploid) (diploid)

Meiosis has 2 stages Meiosis has 2 stages – Meiosis I:Meiosis I: Separation of homologous chromosomes Separation of homologous chromosomes

(different than mitosis)(different than mitosis)– Meiosis II:Meiosis II: Separation of sister chromatids (almost Separation of sister chromatids (almost

identical to mitosis)identical to mitosis)

MEIOSIS IMEIOSIS IMain eventMain event::Separation of Separation of homologous pairs of homologous pairs of chromosomeschromosomes

What do you notice about What do you notice about the names of the stages?the names of the stages?What do you notice about What do you notice about the movements of the the movements of the genetic material during the genetic material during the stages?stages?

Homologous Pairs:Homologous Pairs: Sets of Sets of same chromosome from same chromosome from different parentsdifferent parents

1. Prophase I1. Prophase I

DNA coils into DNA coils into chromosomeschromosomesNuclear envelope & nucleolus break downNuclear envelope & nucleolus break downSynapsisSynapsis = homologous chromosomes = homologous chromosomes pair up into pair up into tetrads tetrads (What does the prefix (What does the prefix “tetra” mean? Think tetrahedron)“tetra” mean? Think tetrahedron)Crossing-overCrossing-over = homologous pairs switch = homologous pairs switch pieces of their chromatidspieces of their chromatidsGenetic RecombinationGenetic Recombination = maternal & = maternal & paternal genetic info get shuffled during paternal genetic info get shuffled during crossing-overcrossing-over

Tetrad

2. Metaphase I2. Metaphase I

Tetrads Tetrads line up in the middle of the cellline up in the middle of the cell– Remember: Remember: MMetaphase = etaphase = mmiddleiddle

Spindle fibers attach at the Spindle fibers attach at the centromerescentromeres of of each homologous chromosome each homologous chromosome (each (each chromosome in the tetrad will have one attached)chromosome in the tetrad will have one attached)

3. Anaphase I3. Anaphase I

Each homologous chromosome moves to Each homologous chromosome moves to the opposite end of the cell (one member the opposite end of the cell (one member of the pair)of the pair)

Independent AssortmentIndependent Assortment = random = random separation of chromosomes, allows for separation of chromosomes, allows for genetic variationgenetic variation– All of the chromosomes from Mom do not go All of the chromosomes from Mom do not go

to one cell, all from dad into the other – they to one cell, all from dad into the other – they are mixed up between the 2 new daughter are mixed up between the 2 new daughter cellscells

4. Telophase I & Cytokinesis I4. Telophase I & Cytokinesis I

Two newly formed cells are Two newly formed cells are haploidhaploid

Each chromosome in the new cells is still Each chromosome in the new cells is still made up of made up of sister chromatids sister chromatids (which contains 2 (which contains 2 identical-ish copies of chromosome; not necessarily identical-ish copies of chromosome; not necessarily identical because of what process?)identical because of what process?)

MEIOSIS IIMEIOSIS IISeparation of Separation of sister chromatidssister chromatidsVeryVery similar to similar to how mitosis lookshow mitosis looks

Sister ChromatidsSister Chromatids = = identical halves of a identical halves of a chromosome that has chromosome that has been duplicatedbeen duplicated

5. Prophase II5. Prophase II

2 newly created cells from 2 newly created cells from Meiosis I Meiosis I start start to divideto divide

6. Metaphase II6. Metaphase II

Chromosomes line up in the middleChromosomes line up in the middle

7. Anaphase II7. Anaphase II

ChromatidsChromatids separate separate

8. Telophase II & Cytokinesis II8. Telophase II & Cytokinesis II

4 new cells, each with half the number of 4 new cells, each with half the number of chromosomes of the original cellchromosomes of the original cell

Let’s ReviewLet’s Review

1.1. What are gametes?What are gametes?2.2. Are gametes produced through Are gametes produced through mitosismitosis

or or meiosismeiosis??3.3. What is separated during meiosis II?What is separated during meiosis II?4.4. What is separated during meiosis I?What is separated during meiosis I?5.5. What is one way that genetic diversity of What is one way that genetic diversity of

daughter cells is daughter cells is increasedincreased during during meiosis? (think about it, we covered 2 meiosis? (think about it, we covered 2 ways in lecture)ways in lecture)

Agenda for today:Agenda for today:

Finish notes (3 or less slides)Finish notes (3 or less slides)

Using available resources, complete Using available resources, complete worksheet. If you are seen not working, worksheet. If you are seen not working, points will be deducted.points will be deducted.– Due tomorrow at the beginning of class. Will Due tomorrow at the beginning of class. Will

be looking at CONTENT, be looking at CONTENT, notnot COMPLETION COMPLETION

Development of GametesDevelopment of Gametes

SpermatogenesisSpermatogenesis = = production of sperm production of sperm cellscells

OogenesisOogenesis = = production of mature production of mature egg cellsegg cells

NondisjunctionNondisjunction

NondisjunctionNondisjunction = = failure of homologous failure of homologous pairs to separate in pairs to separate in Meiosis IMeiosis I

If an organism If an organism survives, it may have survives, it may have a genetic disordera genetic disorder

PolyploidyPolyploidy

PolyploidPolyploid = = organisms with more organisms with more than the usual than the usual number of number of chromosome setschromosome sets

Occurs frequently in Occurs frequently in plants, results in plants, results in plants that are larger plants that are larger than normalthan normal

http://cellsalive.com/meiosis.htmhttp://cellsalive.com/meiosis.htm

Mitosis vs. MeiosisMitosis vs. Meiosis

MitosisMitosis

Body cellsBody cells

2 cells produced2 cells produced

Diploid (2 of each Diploid (2 of each chromosome)chromosome)

Genetically identical Genetically identical to each other AND to to each other AND to the original cellthe original cell

MeiosisMeiosis

Sex cells (sperm/egg)Sex cells (sperm/egg)

4 cells produced4 cells produced

Haploid (1 of each Haploid (1 of each chromosome)chromosome)

Genetically differentGenetically different