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