REVIEW- MITOSIS Cell Cycle Chromatin Condenses Go At Cell Maturity Chromosome now 2 sister...
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Transcript of REVIEW- MITOSIS Cell Cycle Chromatin Condenses Go At Cell Maturity Chromosome now 2 sister...
R E V I E W-M I T O S I S
CellCycl
e
Chromatin
Condenses
GoAt Cell
Maturity
Chromosome now 2 sister chromatids
Chromatin, Condensed DNA, Chromosomes
95% of the time Easily Visible, 5% of the time
One
Chromatid
Chromosome Replication
Homologous Chromosomes vs Sister Chromatids
TWO TYPES OF CELLS:SOMATIC and GAMETES
SOMATIC: (Body Cells) (Body cells: skin/muscle/liver/bone/brain/blood)
Diploid Cells (2n): The # of chromosomes in a somatic cell 2n = 46 in humans…varies/species
GAMETES: (Sex Cells)(Sex cells = Gametes = Humans?) 23 Sperm + 23 Egg = 46 Zygote (The fertilized egg)
Haploid Cells (n): The # of chromosomes in a sex cell n = 23 in humans (half a complete set)
2n…n…difference?
Not the NUMBER of chromosomes but the SIZE, COMPLEXITY, and amount of DNA
Chromosomes are counted on karyotypes
Human Somatic Cell:46 chromosomes
23 pairs44 autosomes
22 pairs2 sex chromosomes
1 pair XX = female XY = male
Allele: Different forms of a gene (Blue, brown eyes)
Down SyndromeTrisomy 21; Nondisjunction at 21
Lab Today…DVD: Visualizing Cell Process, DNA, Stages of Mitosis
Onion Root Tip……Interphase and PMAT
DVD: Visualizing Cell Process- DNA- Stages of Mitosis ~30sec
Interphase
Telephase with cell plate
Metaphase
Anaphase
Prophase
Meiosis- Key Differences from Mitosis
1. Meiosis reduces the # of chromosomes by half
2. Daughter cells differ from parent and each other
Mitosis- Daughter Cells are Identical (Somatic)Meiosis- At end 4 different cells….Genetic Variation
3. Meiosis involves TWO divisions; Mitosis only one.
Meiosis- Key Differences from MitosisMitosis Creates Body Cells; Meiosis creates Sex cells
1. Meiosis I (PMAT I) involves:Prophase: homologous chromosomes pair up – called
a ‘tetrad’. = Where Crossing Over of non-sister chromatids takes place. *First source of Genetic Variation- no longer identical.
Metaphase I: Homologous pairs line up on the equator- double file- Mom with sister chromosome, dad with sister chromosome. (Double 23 across, not 46) *Independent Assortment- second source of genetic variation
Anaphase I: Tetrad Splits- Sister chromatids do NOT separate at the centromere. (Pair of homologous chromatids split up)
Crossing Over Independent Assortment
23..STILL Replicated
MEIOSIS II: Separating Sister Chromatids
* Do NOT COPY
DNA again
23..
Sin
gle
File All
‘n’
Crossing Over
Prophase IFirst Source of
Genetic VariationChiasmata- sites of
crossing over, occur in synapsis- exchange of genetic material between non-sister chromatids
No longer Genetically Identical
Independent Assortment: Metaphase I2nd Source of Genetic Variation
At least (223)8 million possible
combinations from EACH parent….
64 TRILLION combinations for a diploid
zygote
Producing truly unique
offspring
Third Source of Genetic Variation:Random Fertilization (which sperm will fertilize the egg?)
Spermatogenesis vs Oogenesis