lecture 1

Chromosomes

Bacillus bodies found in the nuclei of eukaryotes during the roles of cell division

Chromosome Theory

Chromosome carry genes

Cell Cycle

A four-stage process in which the cell increases in size, copies its DNA, prepares to divide, and divides

Interphase include

G1,S, and G2

The cell spends most of its time in

Interphase

G1 phase

Protein, enzymes, and types of RNA are formed

S phase

DNA replication / DNA synthesis

G2 phase

Complete the mitosis need of proteins and prepare for the mitotic processes

Where are chromosomes studied in plants

root-tip

Where are chromosome studied in animals

Embryos, cells of the blood, and spinal cord

Why can we only study chromosomes from young non mature cells

The cells are active in either mitosis or meiosis

Somatic cells

Diploid (2n) , pairs of 2 homologous chromosomes

Sex cells

Haploid (1n), present in a mono state

The best phase to study sex cells

Prophase 1

The best phase to study somatic cells

Metaphase

Karyotype

Normal karyotype in humans has

23 pairs

which number is the sex chromosome in a Human karyotype

23

Characteristics of a chromosome in a chromosome group study

1. Size

2. Centromere

3. Secondary constriction

4. Satellite

5. Chromomeres

6. Heterophknosis

7. Chromosome bands

Long chromosome

30 microns

where are long chromosome found

Onions

Short chromosomes

1 micron

Where are short microns found

Fungus

What’s the avg size of chromosomes

6 microns

Centromeres

A specialized DNA sequence of a chromosome that links a pair of sister chromatids

Another name for Centromeres

Primary Constriction

Why are centromeres one of the most important part of chromosomes

controls the movement of chromosome to the poles of the cell during its division by attaching to the spindle fibers

What happens if a centromere region of a chromosome is lost

The chromosome cannot move (doesn’t go to the poles) which leads to It becoming a chromosomal fragment

Metacentric chromosome

Submetacentric chromosome

Acrocentric chromosome

Telocentric chromosome

Dicentric chromosome

Contains 2 centromeres

Secondary constriction

Narrow region found at any point of the chromosome other than that of centromere

Secondary constriction function

1. The disappearance and formation of the nucleus (in a region called nuclear organizing region )

2. Distinguish between chromosomes

Chromosomal Satellite

Part of the end of a chromosome that is separated from the rest of the chromosome by a secondary constriction

Who coined the term chromosomal satellite

Muller in 1938

Chromomeres

Spherical granules are arranged on the chromosome

Where do chromomeres appear

Prophase 1 (meiosis)

Chromomere

Heteropyknosis

The ability to distinguish regions on a chromosome according to the interaction of the chemical components contained in these regions with specific pigments

What specific pigments can be distinguished

1. Hematoxylin

2. Feulgen

3. Carmen

Euchrematin

Do not take up the dye directly ( region of active chromatin ) - contain genes.

Meterochromatine

Region that accept the dye the most ( region of inactive chromatin.) - Doesn't contain genes

Chromosome bands

Each chromosome arm is divided into region, that can be seen using a microscope and special stain

Q -band

Quinacrine pigment - lack continuous fluorescence of chromosomal bundles

G-band

Gems pigments - continuous fluorescence of chromesomal bundles

R-band

Modified giemsa dye- became more visible

Polytene Chromosome

Polytene Chromosome

Large chromosome which have thousands of DNA strands (Known as giant chromosomes)

Where are polytene chromosome found

Salivary glands of insects

How are polytene chromosomes formed

Repeated rounds of DNA replication without cell division

Super Chromosome

Super Chromosome

Consist of about a million adherent chromatids, and the amount of DNA these chromosomes contain may be 32 times that of normal cells

Where are Super chromosome found

Salivary glands of some insects after being infected with one of the micro-parasite ( genus thelophania)

Lamp brush chromosomes

When does lamp brush chromosome appears

Prophase 1 stage of meiosis (especially in diplotine stage)

B-Chromosome

B-chromosome

Accessory chromosome that are mostly inactive chromatin, they carry no genetic information. They have no fixed number in the cells (1 to 30)

Where are B-Chromosome found

Corn