BIOL 2500 - Topic 7 (part 1)

Every species on Earth varies in…

1.) Chromosome structure

2.) Chromosome number in the nucleus

Chromosome structure

It follows a specific pattern of sizes and shapes, with there being 3-4 general chromosome shapes found in most species

Chromosome organization in the nucleus

Within the nucleus, chromosomes occupy territories, such that if you are looking for chromosome 2, you can always find it in the territory it is in

Chromosomal territories

Each territory contains a single chromosome within an arbitrary region that is not bound by any membrane

Karyotype

A visual image of all the chromosomes, from biggest to smallest, which are fluorescently labelled to help us see the bands

General number of chromosomes

1.) Chromosomes 1-22 are autosomes

2.) Chromosome 23 is a sex chromosome

Different types of chromosomes

There are four different chromosome types, based on the position of the centromere and the length of the chromosome arms

Chromosome arms are usually ________ in length

Unequal

Chromosome arms

Short arm (p)

Long arm (q)

4 different types of chromosome shapes

1.) Metacentric chromosomes

2.) Submetacentric chromosomes

3.) Acrocentric chromosomes

4.) Telocentric chromosomes

Metacentric chromosomes

The centromere is near the middle, therefore the p arm = q arm

Submetacentric chromosomes

The centromere is slightly nearer to one end, therefore p arm < q arm

Acrocentric chromosomes

The centromeres are at the very end, therefore p arm (very) << q arm

Telocentric chromosomes

They have a terminal centromere, therefore they only have q no p

Most common types of chromosomes

Submetacentric and acrocentric chromosomes

Visualizing chromosomes

As chromosomes condense for cell division, we can use various staining and fluorescent dyes to highlight regions on the chromosomes, allowing us to see the banding patterns

Significance of banding pattern

It helps ID chromosomes, as each chromosome has a specific banding pattern

What causes the banding patterns we see?

Chromatin condensation

Euchromatin

1.) Regions that are less compact, usually those being actively transcribed

2.) Some are always in this form, such as rRNA genes

Heterochromatin

1.) Regions that are highly compact, resulting in less gene transcription

2.) Some are always in this form, such as Barr bodies

Can heterochromatin be found in G1 and G2?

Yes, specifically at genes that are not being transcribed