There are two types of chromosomes found in cells:- autosomes- sex chromosomes

Your body cells have 23 pairs ofchromosomes

- homologous pairs of chromosomes have the same structure- for each homologous pair, one chromosome comes from each parent

Chromosome pairs 1-22 are autosomes.

Sex chromosomes, X and Y, determinegender in mammals.

XX =XY =

femalemale

Bio NOTES: Chromosomes and Meiosis

HOMOLOGOUS CHROMOSOMES

• SAME SIZE• SAME SHAPE• CARRY GENES for the SAME TRAITS

• BUT ______________! (Don’t have to have the SAME CHOICES)

Image modified by Riedell

http://sps.k12.ar.us/massengale/genetics%20tutorial.htm

NOT IDENTICAL

Body Cells

- also called somatic cells- body cells are diploid

Diploid (2n) cells – have two copies of every chromosome

- half the chromosomes come from each parent

Gametes

- also known as sex cells (sperm and egg)- gametes have DNA that can be passed to offspring- gametes are haploid

Haploid (n) cells – have one copy of each chromosome

- gametes have 22 autosomes and 1 sex chromosome

Key Terms •Diploid refers to complete chromosome sets in a cell (or 2N)

• N= the number of chromosomes in a gamete (sex cell)

• N chromosomes from the female parent + N chromosomes from the male parent= 2N

• For humans, 2N = 46

Key Terms •Haploid refers to single chromosomes in a cell (or N)

• One-half of the 2N set (the maternal N or the paternal N)

• Gametes (i.e. sperm, egg sex cells) are haploid cells

• For humans, N = 23

Bottom Line

•diploid means there are the full number of chromosomes in cells

•haploid means that there are half the number of chromosomes in cells

Mitosis and meiosis are types of nuclear division that make different types of cells.

Mitosis- occurs in somatic cells- makes 2 diploid cells- Produces somatic cells

that are genetically Identical

Meiosis- occurs in sex cells (gametes)- makes 4 haploid cells - produces gametes that are

genetically Unique

MEIOSIS10-1

Making gametes…

http://waynesword.palomar.edu/lmexer2a.htm

EGG + SPERM

If egg and sperm had same number of chromosomes as other body cells . . . baby would have too many chromosomes!

http://www.angelbabygifts.com/Image by Riedell Image by Riedell

http://www.acmecompany.com/stock_thumbnails/13217.forty-six_chromosomes.jpg

MEIOSIS is the way…

to make cells with ½ the number of chromosomesfor sexual reproduction

http://waynesword.palomar.edu/lmexer2a.htm

Cells go through two rounds of division in meiosis:

Meiosis reduces the chromosome number and creates genetic diversity.

homologous chromosomes

sisterchromatids

sisterchromatids

• Meiosis I and meiosis II each have four phases, similar to those in mitosis• During meiosis I – pairs of homologous chromosomes separate

- homologous chromosomes are similar, but not identical• During meiosis II – sister chromatids divide

- sister chromatids are copies of the same chromosome

Meiosis I• Meiosis I occurs after DNA has been replicated in interphase• Meiosis I divides homologous chromosomes in four phases: prophase I metaphase I anaphase I telophase I• After cytokinesis, two cells are produced with one homologous chromosome each

Meiosis II

• Meiosis II divides sister chromatids in four phases: prophase II metaphase II anaphase II telophase II

• DNA is not replicated between meiois I and meiosis II

• After cytokinesis, four new cells are produced, each with half the chromosome number (haploid)

Stop here day 1

• Option 1• Work on Vocab List

• Option 2• Complete Web quest

MITOSIS vs MEIOSISINTERPHASE INTERPHASE I

• DNA is spread out as chromatin• Nuclear membrane/

nucleolus visible• DNA is copied during S phase• Makes stuff new cell needs in G2

SAME AS MITOSIS

http://www.pbs.org/wgbh/nova/baby/divi_flash.html

MITOSIS vs MEIOSIS PROPHASE PROPHASE I

• DNA scrunches into chromosomes

• Nuclear membrane/ nucleolus disappear

• Centrioles/spindle fibers appear

DNA scrunches into chromosomesNuclear membrane/ nucleolus disappear Centrioles/spindle fibers appear

Homologous pairs match upCROSSING OVER OCCURS!

http://www.pbs.org/wgbh/nova/baby/divi_flash.html

WHAT MAKES MEIOSIS DIFFERENT?

1. Exchange of DNA betweenhomologous pairs = _____________during PROPHASE I

CROSSING OVER

Allows shuffling of genetic material

http://www.emc.maricopa.edu/faculty/farabee/BIOBK/Crossover.gif

Click the image to play the video segment. 11E

Video 5

Crossing Over

SEE CROSSING OVERANIMATION

CROSSING OVER

• Allows for_________________in different combinations

• After crossing over, chromatid arms are________________ anymore

Image modified by Riedell

http://sps.k12.ar.us/massengale/genetics%20tutorial.htm

rearranging of DNA

NOT IDENTICAL

MITOSIS vs MEIOSIS METAPHASE METAPHASE I

• Chromosomes line up in middle

HOMOLOGOUS Chromosomes line up in middle

http://www.pbs.org/wgbh/nova/baby/divi_flash.html

.Independent assortment occurs

METAPHASE I

• Spindle fibers attach to the centromeres

• Homologous Chromosomes Line up at the equator

• chromosome pairs line up randomly in cell

MITOSIS vs MEIOSIS ANAPHASE ANAPHASE I

APART:Chromatids split

APART:

http://www.pbs.org/wgbh/nova/baby/divi_flash.html

Chromatids stay togetherHomologous pairs split

MITOSIS vs MEIOSIS TELOPHASE TELOPHASE I

See TWO nucleiNuclear membrane/ nucleolus returnDNA spreads out as chromatinSpindle/centrioles disappear

SAME

http://www.pbs.org/wgbh/nova/baby/divi_flash.html

MITOSIS vs MEIOSIS CYTOKINESIS CYTOKINESIS I

Cytoplasm splits into 2 cells

SAME AS MITOSIS2 Genetically Different Haploid Cells Form

http://www.pbs.org/wgbh/nova/baby/divi_flash.html

MITOSIS vs MEIOSIS INTERPHASE II

• DNA is spread out as chromatin• Nuclear membrane/

nucleolus visible• DNA is copied during S phase

SKIP INTERPHASE IIDNA NOT COPIED

http://www.pbs.org/wgbh/nova/baby/divi_flash.html

MITOSIS vs MEIOSIS PROPHASE PROPHASE II

• DNA scrunches into chromosomes

• Nuclear membrane/nucleolus disappear

• Centrioles/ spindle fibers appear

SAME AS MITOSIS

http://www.pbs.org/wgbh/nova/baby/divi_flash.html

MITOSIS vs MEIOSIS METAPHASE METAPHASE II

• Chromosomes line up in middle SAME AS MITOSIS

http://www.pbs.org/wgbh/nova/baby/divi_flash.html

MITOSIS vs MEIOSIS ANAPHASE ANAPHASE II

Sister Chromatids split and move apart

SAME AS MITOSIS

http://www.pbs.org/wgbh/nova/baby/divi_flash.html

MITOSIS vs MEIOSIS TELOPHASE TELOPHASE II

Two nucleiNuclear membrane/

nucleolus returnsCentrioles/spindle fibers

disappearDNA spreads out as chromatin

Same as Mitosis

http://www.pbs.org/wgbh/nova/baby/divi_flash.html

MITOSIS vs MEIOSIS CYTOKINESIS CYTOKINESIS II

Cytoplasm splits2 diploid Genetically Identical cells

SAME AS MITOSIS4 haploid Genetically unique Cells

http://www.pbs.org/wgbh/nova/baby/divi_flash.html

http://www.pbs.org/wgbh/nova/baby/divi_flash.html

Stop Here day 2

• Complete Vocab and SG sheet due by end of class.

Ways Meiosis is different?•Homologous pairs match up & trade DNA (&CROSSING OVER) in PROPHASE I

• INDEPENDENT ASSORTMENT in metaphase I

creates genetic recombination

• Skipping INTERPHASE II- (Dividing TWICE but copying DNA once)

produces 1n cells

Sources of Variations and DifferencesCrossing over

Random assortment of chromosomes

Fertilization

• occurs during prophase I• homologous chromosomes swap pieces• this chromosome swapping creates variations

• chromosome pairs line up randomly in cell• when the pairs separate, this creates cells with genetic variations

• which sperm gets to the egg first?? • it is random and can create variations in offspring