the chromatin is arranged in domains
individual chromosomes can then be identified based on banding patterns
G-banding – treat chromosomes with trypsin (enzyme)
R-banding – heat chromosomes to partially denature DNA
Q-banding - treat chromosomes with the chemical quinacrine
C-banding - treat chromosomes with harsh chemicals to extract
based on the staining pattern generated for each chromosome, one can identify individual
chromosomes and prepare karyotypes
bands, produced by the methods just mentioned, are consistent chromosomal landmarks
a karyotype is described by:
1)
2)
3)
4)
Abnormalities include: t = translocation
dup = duplication
del = deletion
ex: 46,XY,del(5p)
ex: 46,XX,t(9;22)(q34q11)
: human genome is divided among 22 autosomes and 2 sex chromosomes
:
: diploid or 2N number of chromosomes
: genes are spread out over all chromosomes
essential features of eukaryotic chromosome
1) telomeres – the ends of chromosomes
1) centromeres –
3) replication origins – sites where enzymes bind to initiate replication
Haploid vs. Diploid Genomes
haploid genome contains one copy of each chromosome (22 + 1 = 23 = N)
the two copies of a chromosome pair have the same genes but may have
different versions of the genes with distinct DNA sequences
alleles
normal conditions with haploid or diploid number of chromosomes is called
variations in the number of haploid sets of chromosomes is called polyploidy
ex: triploid =
change in chromosome number that involves less than an entire diploid set of
chromosomes is called aneuploidy
ex: monosomy (2N-1) =
ex: trisomy (2N+1) =
When cells prepare to divide, thin strands of chromatin begin to condense into coiled structures, ultimately forming chromosomes
These highly coiled chromosomes then can be viewed with a microscope
Chromosomes exist as pairs or homologues where one member of the pair is derived from the female parent and the other from the male parent.
zygote
Does a greater number of chromosomes mean a more complex organism?
ex: chimp/gorilla = 48
ex: dog/chicken = 78
ex: mouse = 40
ex: fruit fly = 8
ex: corn = 20
Why do dogs and chickens have more chromosomes than humans?
The interval between divisions
cell cycle
mitosis and cytokinesis
mitosis
cytokinesis
*growth and synthesis
Two stages of the cell cycle:
1) interphase –
3 phases to interphase:
1) G1 (gap 1) –
2) S (synthesis) –
3) G2 (gap 2) –
The time spent by a cell in interphase varies between 18-24 hrs
some cells continually cycle through mitosis
ex:
while others stop in interphase and do not proceed to the next division
ex: cells of the nervous system –
This is what happens in the case of spinal cord injuries
in between are cells which are arrested in G1 or G2 that can be stimulated to
proceed through interpahse and into cell division
ex: epidermal (skin) cells
The regulation of this part of the cell cycle is very because
2) mitosis –
cytokinesis is not too precise
however, the division and distribution of chromosomes must be accurate
mitosis can be divided into 4 stages:
1) prophase –
chromatids
sister chromatids
2) metaphase –
3) anaphase –
4) telophase –
Mitosis is an essential process
The mechanism that determines whether cells are cycling or noncycling operates in
It has been established that each species has a characteristic life span
Cells cultured from human embryos have a limit of about 50 doublings
This programming must be under genetic control
progeria –