Microscope Type Electron Research Paper

Microscope Type Electron (Transmission Electron Microscope AKA TEM) Light (Optical Microscope)

Cell Components Seen Organelles, through to the point of being able to observe inside the nucleus Smallest observable organelle, ribosome. Cell structure

Smallest visible Organelle, mitochondrion.

Specimen Preparation Specimen is stained with materials such as lead, osmium and uranium salts. The salts are then absorbed by the organelles and cell membrane, but not the cytoplasm. This means that the electrons cannot pass through the salt. Allowing there to be dark and light areas in the image created. This is done to prevent the image from being distorted through collision between electrons and air particles. (John Parker, 2000)

Place specimen

, Mitosis involves a cell copying itself and then replicating itself, requiring only one nuclear division. Creating two diploid (46 chromosomes) daughter cells which are identical to the parent. , The cell replicates the homologous pairs, as with mitosis. This happens in meiosis (I). There is further division as the daughter cells split into haploid gametes (23 chromosomes). Altogether through meiosis you end up with 4 genetically different daughter cells. This occurs during meiosis (II).

(ii) Chromosomes replicate before they can be seen in a stained cell. , When chromosomes are preparing to replicate, the chromatin (bunched up single strand DNA winds around the histone proteins, eventually appearing in the form that can be stained. , The chromosomes prepare to replicate before meiosis (I) in an identical fashion as mitosis.

(iii) Involves the formation chiasmata. , Chiasmata only occur during the crossing over phase of meiosis; therefore it cannot occur in mitosis. , Chiasmata form at the points where 2 sister chromatids cross over, swapping a small section of genes, this creates new variations in the genetic

Firstly the homologous pairs (same) will come close together in what is called the bivalent (think of soldiers standing in rank). After this, the chromatids will wrap and split off, swapping chromosomes.

• In the fusion of two sex cells (sperm and egg) where the 23 chromosome from each gamete will fuse together to form a diploid zygote, this contains the full new genetic code that will be used through mitosis to develop the zygote into a full multicellular organism (foetus).

• In meiosis (I) the homologous pairs stack, before being pulled apart and used in the daughter cells. When referring only to chromosome 21, on occasion, mostly in egg production, the sister chromatids can be pulled apart unevenly, with 3 chromatids going into one daughter cell, and one chromatid going to the other. This means that if nondisjunction occurs in meiosis (I), when meiosis (II) occurs, there will be 2 gametes with 3 chromosome-21s going into telophase, and 2 gametes with only one chromosome-21. This is referred to as trisomy-21. This can also occur in meiosis (II) where meiosis (I) occurs normally but there is nondisjunction in the daughter cell resulting in 2 gametes with 2 chromosome-21s, a gamete with 3 chromosome-21s and a gamete with only a single