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

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 J WERBA – IB BIOLOGY 2

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. J WERBA – IB BIOLOGY 3

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. J WERBA – IB BIOLOGY 4

COMPARE PROKARYOTES and EUKARYOTES J WERBA – IB BIOLOGY 5

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. J WERBA – IB BIOLOGY 6

PROKARYOTIC CHROMOSOMES U.1 U.2 J WERBA – IB BIOLOGY 7

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. J WERBA – IB BIOLOGY 8

COMPARE PROKARYOTES and EUKARYOTES FEATURE PROKARYOTIC EUKARYOTIC Shape Circular Linear Contains DNA DNA & proteins Location Cytoplasm Nucleus J WERBA – IB BIOLOGY 9

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 J WERBA – IB BIOLOGY 10

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 J WERBA – IB BIOLOGY 11

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 J WERBA – IB BIOLOGY 12

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. J WERBA – IB BIOLOGY 13

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. J WERBA – IB BIOLOGY 14

THE CAIRNS’ TECHNIQUE U.5 J WERBA – IB BIOLOGY 15

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 J WERBA – IB BIOLOGY 16

GENOME SIZE U.8 The total number of nucleotide base pairs within one copy of a single genome. J WERBA – IB BIOLOGY 17

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 J WERBA – IB BIOLOGY 18

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) 150 000 x 106 Protopterus aethiopicus (marbled lungfish) 130 000 x 106 J WERBA – IB BIOLOGY 19

GENOME SIZE U.8 Japanese native pale- petal = largest known plant genome Marbled lungfish = largest known vertebrate genome J WERBA – IB BIOLOGY 20

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 J WERBA – IB BIOLOGY 21

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. J WERBA – IB BIOLOGY 22

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) J WERBA – IB BIOLOGY 23

KARYOTYPING U.9 J WERBA – IB BIOLOGY 24

KARYOTYPING MALE KARYOGRAM FEMALE KARYOGRAM U.9 A.4 J WERBA – IB BIOLOGY 25

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 J WERBA – IB BIOLOGY 26

USING GENETIC DATABASES http://www.ncbi.nlm.nih.gov/gene 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 J WERBA – IB BIOLOGY 27

CHROMOSOMES Q1. In the following diagram, which pair represents homologous chromosomes? 1 and 2 3 and 4 2 and 5 4 and 6 J WERBA – IB BIOLOGY 28

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 J WERBA – IB BIOLOGY 29

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) J WERBA – IB BIOLOGY 30