there are two types of chromosomes found in cells: - autosomes - sex chromosomes your body cells...
TRANSCRIPT
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