Law of inheritance

Proposed genetic factors

Chromosomal theory

Real observation of division of genetic elements

Genetic analysis

extentions

Mitosis and meiosisCell cycle

AneuploidRecombinationGene conversion

Evidence that Genes Reside in the Nucleus

• 1667 – Anton van Leeuwenhoek– Microscopist– Semen contains spermatozoa (sperm animals)– Hypothesized that sperm enter egg to achieve fertil

ization• 1854-1874 – confirmation of fertilization throu

gh union of eggs and sperm– Recorded frog and sea urchin fertilization using mic

roscopy and time-lapse drawings and micrographs

Evidence that Genes Reside in Chromosomes

• 1880s – innovations in microscopy and staining techniques identified thread-like structures

• Provided a means to follow movement of chromosomes during cell division

• Mitosis – two daughter cells contained same number of chromosomes as parent cell (somatic cells)

• Meiosis – daughter cells contained half the number of chromosomes as the parents (sperm and eggs)

Hippocrates (460-350 BC)

19th century

Pangenesis Chromosomal theory

A gradual process

Key observation1883 E. van Beneden

The egg and sperm contributes equal number of chromosomes to the fertilized egg

Boveri Centriols of ascaris

Reproduction as the basis of heredity

Cells – prokaryotes, eukaryotes ( with membrane-bound organelles)ChromosomesMitosis (-thread– cell cycle, cell divisionMeiosis (-reduction– oogenesis and spermatogenesis - meiosis in plantsLife cycle

Principle of Genetics Chapter 2Cell 112:423-440 2003

Deviding E.coli

DNA

An interphase eukaryotic cells

Cell division

*proper distribution of genetic materials into daughter cells

- separation of chromosomes

Chromosomes

•Transmission of genetic materials• orderly releases of genetic information ( gene regulation)

The structure of replicated chromosome

The cell cycle ( mammalian cells in tissue culture)

cell massDuplication of genetic materialDivision for equal distribution of genetic material

order

The mitotic spindle in a cultured animal cell

asters

Centrosome(MTOC)

Centriols(surrounded by pericentriolar material –initiation of formation of the microtubules)

Mitosis

Identical daughter cells

cytokinesis

2n 2n

Parental cells

Daughter cells

TimeEventsCoordination

Three-Dimensional Maps of All Chromosomes in Human Male Fibroblast Nuclei and Prometaphase Rosettes(PLoS Biol. 2005 May;3(5):e157. Epub 2005 Apr 26. )

chromatinChromosome(condensed)

cytokinesis

Animal cells A cleavage furrow Plant cells: Formation of a cell plate

Chromosome : sister chromatid cohesion and separation (cohesin)chromosomal condensation and decondensation (condensins, topoisomerase II)

Microtubules : spindle formation (cetrosomes, asters)

Microtubule – chromosome interaction: kinetochore formation

Meiosis

Meiosis

1883 Edouard van Beneden

# of chromosome Eggs of round worm = ½ somatic cells

1st meiotic division - reduction division (separation of homologous chromosomes)

2nd meiotic division - equatorial division(separation of sister chromatid)

Zygonema Pairing Homologous chromosomes

**synapsis

crossing over

The synaptinemal complex

Crossing over

chromomeres

**synapsis crossing overchiasmatasdisappearance of synaptal complex

towards the center of nucleus

Chiasmata

Neurospora crassa

One gene – one enzyme

1st meiotic division

2nd meiotic division

Life cycle – the sequence of events from fertilization to death a few examples

Ordered meiosis

Saccharomyces cerevisiae

Easy to grow, easy to manipulate

Meiosis and mitosis in plants

Meiosis gametogenesis

Drosophila melanogaster

Early embryologenesis

After puberty

Oogenesis in femalespermatogenesis

Beyond meiosis

Unequal distribution of cytoplasm

differentiation

After puberty

nonmotile

With meiotic program

Diplotene diplonema

1/month

Asymtrical cytokinesis

Hormone effect

differentiation