1. CHROMOSOMES Topic 3.2 IB Biology Miss Werba
Chromosomes carry genes in a linear sequence that is shared by members of a species.
Topic 3.2
IB Biology
Miss Werba

2. GENETIC MODIFICATION and BIOTECHNOLOGY
TOPIC 3 – GENETICS
3.1
GENES
3.2
CHROMOSOMES
3.3
MEIOSIS
3.4
INHERITANCE
3.5
GENETIC MODIFICATION and BIOTECHNOLOGY
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3. THINGS TO COVER U.1 U.2 U.3 U.4 U.5 U.6 U.7 U.8 Statement Guidance
Prokaryotes have one chromosome consisting of a circular DNA molecule.
U.2
Some prokaryotes also have plasmids but eukaryotes do not.
U.3
Eukaryote chromosomes are linear DNA molecules associated with histone proteins.
U.4
In a eukaryote species there are different chromosomes that carry different genes.
U.5
Homologous chromosomes carry the same sequence of genes but not necessarily the same alleles of those genes.
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
U.6
Diploid nuclei have pairs of homologous chromosomes.
U.7
Haploid nuclei have one chromosome of each pair.
U.8
The number of chromosomes is a characteristic feature of members of a species.
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4. THINGS TO COVER U.9 U.10 A.1 A.2 A.3 A.4 S.1 Statement Guidance
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.
U.10
Sex is determined by sex chromosomes and autosomes are chromosomes that do not determine sex.
A.1
Cairns’ technique for measuring the length of DNA molecules by autoradiography.
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.
A.3
Comparison of diploid chromosome numbers of Homo sapiens, Pan troglodytes, Canis familiaris, Oryza sativa, Parascaris equorum.
A.4
Use of karyograms to deduce sex and diagnose Down syndrome in humans.
S.1
Use of databases to identify the locus of a human gene and its polypeptide product.
NOS 1.8
Developments in scientific research follow improvements in technology.
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5. COMPARE PROKARYOTES and EUKARYOTES
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6. PROKARYOTIC CHROMOSOMES
U.1
U.2
The prokaryotic chromosome is located in the cytoplasm.
Prokaryotes have one chromosome consisting of a circular DNA molecule.
Some prokaryotes also have plasmids (eukaryotes do not)
Plasmids are small loops of DNA that can be passed between organisms
There are no proteins within prokaryotic chromosomes.
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7. PROKARYOTIC CHROMOSOMES
U.1
U.2
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8. EUKARYOTIC CHROMOSOMES
The eukaryotic chromosomes are located in the nucleus.
Eukaryotes have multiple chromosomes consisting of a linear DNA molecules.
each chromosome carries different genes
There are histone proteins associated with the eukaryotic chromosomes.
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9. COMPARE PROKARYOTES and EUKARYOTES
FEATURE
PROKARYOTIC
EUKARYOTIC
Shape
Circular
Linear
Contains
DNA
DNA & proteins
Location
Cytoplasm
Nucleus
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10. HOMOLOGOUS CHROMOSOMES
Homologous chromosomes are chromosomes that share the same structural features and the same sequence of genes, but may have a different combination of alleles
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11. HOMOLOGOUS CHROMOSOMES
Haploid nuclei:
One set of chromosomes (one from each pair)
In humans, number (n) = 23
In humans, gametes (sperm & ova) are haploid
Diploid nuclei:
Two sets of chromosomes (pairs of homologous chromosomes)
In humans, 2n = 46
In humans, all body cells (other than gametes) are diploid
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12. NUMBER OF CHROMOSOMES
U.8
A.3
The number of chromosomes is a characteristic feature of members of a species.
ORGANISM
DIPLOID CHROMOSOME NUMBER
Homo sapiens (human) 46
Pan troglodytes (chimp) 48
Canis familiaris (domestic dog) 78
Oryza sativa (rice) 24
Parascaris equorum
(parasitic worm) 2
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13. Developments in scientific research follow improvements in technology
THE CAIRNS’ TECHNIQUE
NOS 1.8
A.1
Developments in scientific research follow improvements in technology
Autoradiography was used to establish the length of DNA molecules in chromosomes.
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14. THE CAIRNS’ TECHNIQUE
U.5
The Cairns’ technique is used for measuring the length of DNA molecules.
Hugh John Forster Cairns used autoradiography to demonstrate that E. coli contain a single, circular molecule of DNA.
Cairns used radioactive markers to “label” the DNA so that he could photograph replication in the bacterium.
The image produced on a photographic plate by radioactivity is called an autoradiograph.
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15. THE CAIRNS’ TECHNIQUE
U.5
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16. THE CAIRNS’ TECHNIQUE
U.5
He observed how cycles of replication occur in bacterium.
He also used the technique to measure the length of DNA molecules
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17. GENOME SIZE
U.8
The total number of nucleotide base pairs within one copy of a single genome.
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18. GENOME SIZE Note that: Genome size does not correlate with complexity
U.8
Note that:
Genome size does not correlate with complexity
Genome size does not correlate with number of genes
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19. GENOME SIZE
A.2
ORGANISM
GENOME SIZE (number of base pairs)
T2 phage (bacteria-infecting virus)
3569
E. coli (bacteria)
4.6 x 106
Drosophila melanogaster (fruit fly)
130 x 106
Homo sapiens (human)
3 200 x 106
Paris japonica
(Japanese native pale-petal)
x 106
Protopterus aethiopicus (marbled lungfish)
x 106
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20. GENOME SIZE
U.8
Japanese native pale- petal = largest known plant genome Marbled lungfish = largest known vertebrate genome
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21. KARYOTYPING
U.9
Karyotyping is the process of arranging the chromosomes in pairs according to their structure.
Chromosomes have unique banding patterns if they are stained with specific dyes.
Chromosomes are easily identifiable and are arranged depending upon:
their length
the position of their centromere
their banding pattern
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22. KARYOTYPING Can be used to detect chromosome disorders in foetuses.
Utilises foetal DNA obtained using chorionic villus sampling or amniocentesis
Can also be used in forensic science.
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23. KARYOTYPING A karyogram shows the karyotype of a cell.
U.9
A karyogram shows the karyotype of a cell.
A karyogram is a photograph or diagram of stained chromosomes, arranged in pairs in order of their size.
It indicates the number of chromosomes present and sex of the individual.
It can be used to test for chromosomal abnormalities involving extra or missing chromosomes:
eg. Down syndrome (three copies of chrom 21)
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24. KARYOTYPING
U.9
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25. KARYOTYPING MALE KARYOGRAM FEMALE KARYOGRAM U.9 A.4
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26. AUTOSOMES & SEX CHROMOSMES
22 pairs (44 total)
Determine non-sexual characteristics
Sex chromosomes:
1 pair
May or may not be homologous (XX vs XY)
Determine sex of individual XX = female XY = male
Determine both sexual and non-sexual characteristics
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27. USING GENETIC DATABASES
Use NCBI to search for the location of the following genes:
BRAC1 – early onset breast cancer gene
MT-CO1 – mitochondrially encoded cytochrome c oxidase I
TTN - titin
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28. CHROMOSOMES
Q1. In the following diagram, which pair represents homologous chromosomes?
1 and 2
3 and 4
2 and 5
4 and 6
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29. CHROMOSOMES
Q2. If the haploid number of a species is 28, how many chromatids will there be in the diploid cell? 7 14 28 56
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30. CHROMOSOMES
Q3. The karyogram below shows the chromosomes from a person with Down syndrome.
[Source: U.S. Department of Energy Human Genome Program (genomics.energy.gov, genomicscience.energy.gov)]
State the evidence provided by the karyogram that shows this person has Down syndrome. (1)
State the gender of this individual and explain your answer. (2)
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