Fatchiyah, Ph.D.

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Chromosome

• Fatchiyah, Ph.D.
• Lab. Molecular Biology
• Brawijaya University

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Chromosome DNA?

• Chromosomes, threadlike structures, first
  observed by Nageli in 1842.
• Walter Flemming was the first to follow the
  process of mitosis and replication of
  chromosomes.
• Thomas Morgan, in his experiments with fruit
  flies, described genetic recombination, and
  demonstrated that traits were to inherited
  together to varying degrees.
• Alfred Sturtevant extended Morgans ideas, used
  observed recombination rates to produce the first
  genetic maps.

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The nucleus is the center of cellular operations

• Surrounded by a nuclear envelope

• Perinuclear space

• Communicates with cytoplasm through nuclear pores

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The Nucleus

• Content of nucleus
• A supportive nuclear matrix
• One or more nuclei
• Chromosomes
• Chromatin
• DNA bound to histones

Figure 3.13
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What Are Chromosomes?

• Cytogenetics is the study of chromosomes and the
  related disease states caused by abnormal
  chromosome number and/or structure.
• Chromosomes are complex structures located in the
  cell nucleus, they are composed of DNA, histone
  and non-histone proteins, RNA , and
  polysaccharides.
• They are basically the "packages" that contain
  the DNA.

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What Are Chromosomes?

• Normally chromosomes can't be seen with a light
  microscope but during cell division they become
  condensed enough to be easily analyzed at 1000X.
• To collect cells with their chromosomes in this
  condensed state they are exposed to a mitotic
  inhibitor which blocks formation of the spindle
  and arrests cell division at the metaphase stage

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Type of chromosome structure

1. The short arm is designated as p and the long arm
   as q.
2. The centromere is the location of spindle
   attachment and is an integral part of the
   chromosome.
3. It is essential for the normal movement and
   segregation of chromosomes during cell division.

Metacentric Chrom. 1
Acrocentric Chrom. 14
Submetacentric Chrom. 9
The ideogram is basically a "chromosome map"
showing the relationship between the short and
long arms, centromere (cen), and in the case of
acrocentric chromosomes the stalks (st) and
satellites (sa). The specific banding patterns
are also illustrated. Each band is numbered to
aid in describing rearrangements.
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Figure 3.14 Chromosome Structure
Figure 3.14
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Organization of Genes on Human Chromosome
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Structural Organization of the Nucleosome
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Structural Organization of the Nucleosome
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Nucleosome Disruption
Figure 4-34. A cyclic mechanism for nucleosome
disruption and re-formation. According to this
model, different chromatin remodeling complexes
disrupt and re-form nucleosomes, although, in
principle, the same complex might catalyze both
reactions. The DNA-binding proteins could
function in gene expression, DNA replication, or
DNA repair, and in some cases their binding could
lead to the dissociation of the histone core to
form nucleosome-free regions of DNA like those
illustrated in Figure 4-30. (Adapted from A.
Travers, Cell 96311 314, 1999.)
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Chromosome Facts

• number of chromosomes 22 pairs 1 pair
  sex-determining chromosomes 46
• one chromosome of each pair donated from each
  parents egg or sperm
• sex chromosomes X,Y for males X,X for females
• largest chromosome 1 263 million base pairs
  (bp)
• smallest chromosome Y 59 million bp

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Chromosomes can be painted for
easyidentification.By technique of
multiplexfluorescence in situ hybridization
(M-FISH)
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Gene Facts

• size of human genome 3.4 billion base pairs
  (bp)
• number of human genes 100,000
• genes vary in length and can cover thousands of
  bases
• avg. size 3,000 bp
• only about 5 of the human genome contains genes
• function of much of the genome is unknown

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Chromosomes come in pairs

• Humans have 23 pairs of chromosomes
• Total of 46 chromosomes
• Fruit flies have 4 pairs of chromosomes
• Total of 8 chromosomes

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Normal Chromosomes

• Normal human somatic cells have 46 chromosomes
  22 pairs, or homologs, of autosomes (chromosomes
  1-22) and two sex chromosomes. This is called the
  diploid number. Females carry two X chromosomes
  (46,XX) while males have an X and a Y (46,XY).
• Germ cells (egg and sperm) have 23 chromosomes
  one copy of each autosome plus a single sex
  chromosome. This is referred to as the haploid
  number.
• One chromosome from each autosomal pair plus one
  sex chromosome is inherited from each parent.
• Mothers can contribute only an X chromosome to
  their children while fathers can contribute
  either an X or a Y.

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Chromosomes of human
Male
Female
Y-chrom
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Members of a chromosome pair

• Cells with PAIRS of chromosomes are diploid
• di means two, double, twice
• oid appearance
• The two members of any chromosome pair are called
  homologues, or a homologous pair
• Ex
• The two number 1 chromosomes are homologues
• The two number 21 chromosomes are homologues.

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In sexual reproduction

• new organisms (zygotes) are formed by the joining
  together of two sex cells (gametes)
• a sperm cell from a male and
• an egg cell from a female

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What would happen if.

• a human egg cell had 46 chromosomes
• AND
• a human sperm cell had 46 chromosomes?

46 chromosomes 46 chromosomes 92
chromosomes Too many for a human!
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Diploid organisms need.

• A way to produce sex cells (eggs and sperm) that
  only have ONE member of each chromosome pair
• In humans, sex cells each have 23 chromosomes
• ONE member of each homologous pair
• Half of amount of chromosome is named genome
  (haploid)

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• 23 chromosomes
• 23 chromosomes
• 46 chromosomes
• Just right for a human!

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The different possibilities of the way
chromosomes will separate into gametes helps
create genetic diversity
OR
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Effect of Crossing Over
Crossing over occurs when homologous chromosomes
pair with each other before the first meiotic
division
Chromatids cross over one another, and the
crossed sections of the chromatids are exchanged.
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Chromosomes
Figure 4-14. Two closely related species of deer
with very different chromosome numbers. In the
evolution of the Indian muntjac, initially
separate chromosomes fused, without having a
major effect on the animal. These two species
have roughly the same number of genes. (Adapted
from M.W. Strickberger, Evolution, 3rd edition,
2000, Sudbury, MA Jones Bartlett Publishers
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The emphasis in the human genome

• Human
• 26,588 genes
• The nervous system
• The immune system
• The blood system
• Signaling and cell-cell communication
• Programmed cell death

• Arabidopsis
• 25, 498 genes
• Missing
• Missing
• Missing
• Different
• Missing

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Structure of Chromosome - NORs
Interphase nucleus of onion root tip through
light microscope
nucleolus
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Structure of Chromosome - NORs
electron micrograph of interphase cell from bat
pancreas
nucleolus
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Polytene Chomosome of Drosophila as Giant
chromosome
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Polytene chromosome
Phase-contrast image of Drosophila
melanogaster polytene cromosomes. A. The end of
the X-chromosome is marked with an arrow.
Chromocentre is in the upper right corner. B.
Shows a magnification of chromomere and
interchromomere bands
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W-chromosome
Yeast Artificial Chromosome
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Bacterial Artificial Chromosome Manipulation by
Homologous Recombinant
(HeintZ, 2001)
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Metaphase Chromosome in middle cell
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Antibodies of a person with an autoimmune disease
stain centromers