Chromosomes carry genes in a linear sequence that is shared by members of a species. In prokaryotes, DNA exists as a single circular chromosome, while eukaryotes have multiple linear chromosomes associated with histone proteins. Homologous chromosomes in diploid cells contain the same genes but can have different alleles. Sex is determined by X and Y chromosomes in most species. Karyotyping allows visualization of chromosomes and can be used for analysis.

1. 3.2 Chromosomes
Essential
Question:
Chromosomes
carry genes in
a linear
sequence that
is shared by
members of a
species.
http://41.media.tumblr.com/4c08ea6
94bcf30c5a9d8423187fba2de/tumblr
_mx5zd49kWN1qjofuoo1_1280.jpg
Stages of Mitosis by Walter Flemming January 1882

2. Understandings
Statement Guidance
3.2.U1 Prokaryotes have one chromosome consisting of a circular DNA molecule.
3.2.U2 Some prokaryotes also have plasmids but eukaryotes do not.
3.2.U3 Eukaryote chromosomes are linear DNA molecules associated with histone proteins.
3.2.U4 In a eukaryote species there are different chromosomes that carry different genes.
3.2.U5
Homologous chromosomes carry the same sequence of genes but not necessarily the same alleles of those
genes.
3.2 U6 Diploid nuclei have pairs of homologous chromosomes.
3.2 U7
Haploid nuclei have one chromosome of each pair. [The two DNA molecules formed by DNA replication prior
to cell division are considered to be sister chromatids until the splitting of the centromere at the start of
anaphase. After this, they are individual chromosomes.]
3.2 U8 The number of chromosomes is a characteristic feature of members of a species.
3.2 U9
A karyogram shows the chromosomes of an organism in homologous pairs of decreasing length. [The terms
karyotype and karyogram have different meanings. Karyotype is a property of a cell—the number and type
of chromosomes present in the nucleus, not a photograph or diagram of them.]
3.2 U10 Sex is determined by sex chromosomes and autosomes are chromosomes that do not determine sex.

3. Applications and Skills
Statement Guidance
3.2 A1 Cairns’ technique for measuring the length of DNA molecules by autoradiography.
3.2 A2
Comparison of genome size in T2 phage, Escherichia coli, Drosophila melanogaster, Homo sapiens and Paris
japonica. [Genome size is the total length of DNA in an organism. The examples of genome and chromosome
number have been selected to allow points of interest to be raised
3.2 A3
Comparison of diploid chromosome numbers of Homo sapiens, Pan troglodytes, Canis familiaris, Oryza
sativa, Parascaris equorum.
3.2 A4 Use of karyograms to deduce sex and diagnose Down syndrome in humans.
3.2 S1 Use of databases to identify the locus of a human gene and its polypeptide product.

4. 3.2 U1 Prokaryotes have one chromosome consisting of a
circular DNA molecule.
• Prokaryotic DNA is
circular and is not
associated with any
histone proteins
• There is one copy of
each gene except
when the cell and its
DNA are replicating
Bacterial
DNA
Plasmids

5. 3.2 U1 Prokaryotes have one chromosome consisting of a
circular DNA molecule.
https://classconnection.s3.amazonaws.com/730/flashcards/127
6730/jpg/cell_types1330806303645.jpg

6. 3.2 U.2 Some prokaryotes also have plasmids but eukaryotes
do not.
http://upload.wikimedia.org/wikipedia/en/6/6c/PBR322_pl
asmid_showing_restriction_sites_and_resistance_genes.jpg
• Plasmids are small separate (usually
circular) DNA molecules located in
some prokaryotic cells
• Plasmids are also naked (not
associated with proteins) and are not
needed for daily life processes in the
cell.
• The genes in plasmids are often
associated with antibiotic resistant
and can be transferred from one
bacterial cell to another.
• Plasmids are readily used by scientists
to artificially transfer genes from one
species to another (ie. Gene for
human insulin)

7. Nucleosome Structure: consist of 8 histones. They help create super coiling of
chromatin, which creates a chromosome during cell replication
3.2 U.3 Eukaryote chromosomes are linear DNA molecules associated with histone proteins.
http://micro.magnet.fsu.edu/cells/nucleus/images/
chromatinstructurefigure1.jpg

8. • Eukaryotic chromosomes are linear
and are made up of DNA and
histone proteins.
• Histones are globular shaped
protein in which the DNA is
wrapped around.
• DNA wrapped around 8 histone
proteins is called a nucleosome.
• The DNA wraps twice around the
histone protein core.
• Another histone protein is attached
to the outside of the DNA strand.
This helps maintain the colloidal
structure of the nucleosome.
• DNA, because of its negative charge
is attracted to the positive charge
on the amino acids of the histone
proteins.
3.2 U.3 Eukaryote chromosomes are linear DNA molecules
associated with histone proteins.
http://upload.wikimedia.org/wikipedia/commons/
4/45/Nucleosome_organization.png

9. 3.2 U4 In a eukaryote species there are different chromosomes
that carry different genes.
https://s-media-cache-
ak0.pinimg.com/originals/4d/d0/7
a/4dd07a61c384abefef3c521bcab
6bad8.jpg
http://dxline.info/img/new_ail/chro
mosome-4.jpg
• Chromosomes are
linear, varying in length
and in position of the
centromere that holds
the sister chromatids
together.
• In humans there are 23
types of chromosomes.
Each chromosome
carries a specific
sequence of genes
along the linear DNA
molecule. The position
where the gene is
located is called the
locus.
Chromosome 1 Chromosome 4
2,000 Genes 1,000 Genes

10. 3.2 U.5 Homologous chromosomes carry the same sequence
of genes but not necessarily the same alleles of those genes.
https://molecularhelix.files.wordpress.com/2011/07/homolg.gif
• Homologous chromosomes
are chromosomes within each
cell that carry the same genes
• One chromosome came from
an individual’s mother and
one from the father
• They have the same shape
and size
• These chromosomes pair up
during meiosis
• Even though these
chromosomes carry the same
genes, they could have
different alleles (different
versions of the same gene)

11. 3.2 U6 Diploid nuclei have pairs of homologous
chromosomes.
• Diploid nuclei have two copies of
each type of chromosome. One
chromosome comes from the
mother and one from the father.
• Haploid gametes (sperm and egg)
fuse during sexual reproduction
which produces zygote with a
diploid nucleus
• This cell will then divide by
mitosis to produce numerous
cells, all with a diploid nucleus
• Each nucleus has two copies of
each gene, accept the sex
chromosomes

12. 3.2 U.7 Haploid nuclei have one chromosome of each pair. [The two
DNA molecules formed by DNA replication prior to cell division are
considered to be sister chromatids until the splitting of the centromere
at the start of anaphase. After this, they are individual chromosomes.]
• Haploid nuclei have one copy of each chromosome or one full set of
the chromosomes in that particular species eg. Human 23
chromosomes
• These are called gametes, which are sperm and egg
• Human sperm and eggs each contain 23 chromosomes
https://classconnection.s3.amazonaws.com/116215/flashcards/771420/png/meiosis-1.png

13. 3.2 U.7 Haploid nuclei have one chromosome of each pair. [The two
DNA molecules formed by DNA replication prior to cell division are
considered to be sister chromatids until the splitting of the centromere
at the start of anaphase. After this, they are individual chromosomes.]
• Chromosome to the right
splits at the centromere.
• This occurs during
Anaphase
• The chromatids move to
opposite poles of the cell
to become chromosomes
in a newly created cell.
Chromosome
With two
Chromatids
Become Two
Chromosome

14. 3.2 U.8 The number of chromosomes is a characteristic
feature of members of a species.
• The chromosome number is a characteristic
feature of that species.
• A chromosome number does not indicate how
complicated an organism might be
• Organisms with different numbers of
chromosomes would unlikely be able to
interbreed
• Chromosome number tends to remain
unchanged over millions of years of evolution;
however, sometimes through evolution
chromosomes can fuse together or split to
change the number of chromosomes an
organism contains
• During human evolution, two ancestral ape
chromosomes fused to produce human
chromosome 2

15. 3.2 U.9 A karyogram shows the chromosomes of an organism in
homologous pairs of decreasing length. [The terms karyotype and
karyogram have different meanings. Karyotype is a property of a cell—
the number and type of chromosomes present in the nucleus, not a
photograph or diagram of them.]
http://upload.wikimedia.org/wikipedia/commons/f/f3/Mapa_gen%C3%A9tico_o_cariograma.jpeg

16. Karyotyping
•A karyotype is a picture of an organism's genetic make-up in which the
chromosomes of a cell have been stained so that the banding pattern
of the chromosomes appear.
•Cells in Metaphase are stained to show distinct parts of the
chromosomes. The cells are then photographed through a
microscope and enlarged.
•The chromosomes are cut from the photograph and arranged
according to size, shape, centromere position, and banding patterns.
http://www.mrothery.co.uk/module2/images/Image214.gif

17. 3.2 U.10 Sex is determined by sex chromosomes and
autosomes are chromosomes that do not determine sex.
• The X and Y chromosome determine the sex
of an individual
• The X chromosome contains over 2000 genes
in comparison to the Y chromosome has less
then 100 genes
• If an individual has two X chromosomes they
will be a female and if they have an X and a Y
chromosome they will be a male
• All other chromosomes are called autosomes
and do not affect the sex of an individual
• The X chromosome has many genes located
on it essential to human development, while
the Y chromosome has a small number of
genes (some of these are shared with the X
chromosome). The rest of the genes on the Y
chromosome are only necessary for male
development
http://images.zeit.de/wissen/gesundheit/2014
-01/y-chromosom/y-chromosom-540x304.jpg

18. 3.2 A.1 Cairns’ technique for measuring the length of
DNA molecules by autoradiography.
• Using the technique of autoradiography
Cairns first supplied the cells with suitable
radioactive material (replaces normal
hydrogen in thymidine).
• Used to selectively label only DNA and will
not label RNA.
• Intact bacterial chromosomes are placed on
slides. These slides are then covered by
photographic emulsion and stored in dark.
• During this storage the particles are emitted
exposing the film
• The photographs show the regions of
labelled DNA.
• The results demonstrated semi-
conservative mode of replication.

19. 3.2 A.2 Comparison of genome size in T2 phage, Escherichia coli, Drosophila
melanogaster, Homo sapiens and Paris japonica. [Genome size is the total length of DNA in an
organism. The examples of genome and chromosome number have been selected to allow
points of interest to be raised
Name Genome Length
(million base pairs)
Number of Genes
T2 phage (Virus) 0.18 300
Escherichia coli
(Bacteria)
5 4,377
Drosophila
melanogaster
(Fruit Fly)
140 17,000
Paris japonica
(Woodland Plant)
150,000 Unknown
Homo sapiens
(Human)
3,000 19-23,000

20. 3.2 A.2 Comparison of genome size in T2 phage, Escherichia coli, Drosophila
melanogaster, Homo sapiens and Paris japonica. [Genome size is the total length of DNA in an
organism. The examples of genome and chromosome number have been selected to allow
points of interest to be raised
Paris japonica
Largest Known Genome

21. 3.2 A.3 Comparison of diploid chromosome numbers of Homo
sapiens, Pan troglodytes, Canis familiaris, Oryza sativa, Parascaris
equorum.
Homo sapiens (46)

22. 3.2 A.3 Comparison of diploid chromosome numbers of Homo sapiens, Pan
troglodytes, Canis familiaris, Oryza sativa, Parascaris equorum.
Pan troglodytes (48)
http://static1.squarespace.com/static/51b89f0ce4b0000660671282/t/540785e0e4b00aec95acf4cb/1409779168825/floandfigan.jpg

23. 3.2 A.3 Comparison of diploid chromosome numbers of Homo
sapiens, Pan troglodytes, Canis familiaris, Oryza sativa, Parascaris
equorum.
Canis familiaris 78
https://c1.staticflickr.com/5/4007/5076413065_6a42962771_b.jpg

24. 3.2 A.3 Comparison of diploid chromosome numbers of Homo
sapiens, Pan troglodytes, Canis familiaris, Oryza sativa, Parascaris
equorum.
Species Name Number of
Chromosomes
Homo sapiens 46
Pan troglodytes 48
Canis familiaris 78
Oryza sativa 24
Parascaris
equorum
2
Rice: Oryza sativa
http://upload.wikimedia.org/wikipedia
/commons/6/65/Oryza_sativa_Kyoto_J
PN_001.JPG
Round Worm:
Parascaris equorum
http://www.vetnext.com/fotos/quizc2a4.jpg

25. Normal Male
3.2 A.4 Use of karyograms to deduce sex and diagnose Down syndrome
in humans.
http://commons.wikimedia.org/wiki/File:NHGRI_human_male_karyotype.png

26. Normal Female
3.2 A.4 Use of karyograms to deduce sex and diagnose Down syndrome
in humans.

27. Male with Down Syndrome: Trisomy 21; mental deficiencies ,
as well as physical abnormalities
3.2 A.4 Use of karyograms to deduce sex and diagnose Down syndrome
in humans.
http://upload.wikimedia.org/wikipedia/commons/6/6f/Trisomie_21_Genom-Schema.gif