CHROMOSOMES Chromosomes carry genes in a linear sequence

CHROMOSOMES Chromosomes carry genes in a linear sequence that is shared by members of a species. Topic 3. 2 IB Biology Miss Werba

TOPIC 3 – GENETICS 3. 1 GENES 3. 5 GENETIC MODIFICATION and BIOTECHNOLOGY J WERBA – IB BIOLOGY 3. 2 CHROMOSOMES 3. 4 3. 3 INHERITANCE MEIOSIS 2

THINGS TO COVER Statement Guidance U. 1 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. 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. 5 Homologous chromosomes carry the same sequence of genes but not necessarily the same alleles of those genes. 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 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. Sex is determined by sex chromosomes and autosomes are chromosomes that do not determine sex. Cairns’ technique for measuring the length of DNA molecules by autoradiography. 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. 2 Comparison of genome size in T 2 phage, Escherichia coli, Drosophila melanogaster, Homo sapiens and Paris japonica. 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 J WERBA – IB BIOLOGY U. 1 U. 2 7

EUKARYOTIC CHROMOSOMES U. 3 U. 4 � 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 & proteins Location Cytoplasm Nucleus J WERBA – IB BIOLOGY 9

HOMOLOGOUS CHROMOSOMES U. 5 � 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 U. 6 U. 7 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, 2 n = 46 ◦ In humans, all body cells (other than gametes) are diploid J WERBA – IB BIOLOGY 11

U. 8 A. 3 NUMBER OF CHROMOSOMES � 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

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

U. 5 THE CAIRNS’ TECHNIQUE � 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

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

U. 5 THE CAIRNS’ TECHNIQUE � 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

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

U. 8 GENOME SIZE Note that: � Genome size does not correlate with complexity � Genome size does not correlate with number of genes J WERBA – IB BIOLOGY 18

A. 2 GENOME SIZE ORGANISM GENOME SIZE (number of base pairs) T 2 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

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

U. 9 KARYOTYPING � 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

U. 9 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

U. 9 KARYOTYPING �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

U. 9 KARYOTYPING J WERBA – IB BIOLOGY 24

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

AUTOSOMES & SEX CHROMOSMES U. 10 � Autosomes: ◦ 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

S. 1 USING GENETIC DATABASES http: //www. ncbi. nlm. nih. gov/gene Use NCBI to search for the location of the following genes: � BRAC 1 – early onset breast cancer gene � MT-CO 1 – mitochondrially encoded cytochrome c oxidase I � TTN - titin J WERBA – IB BIOLOGY 27

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

CHROMOSOMES Q 2. If the haploid number of a species is 28, how many chromatids will there be in the diploid cell? 7 B. 14 C. 28 D. 56 A. J WERBA – IB BIOLOGY 29

CHROMOSOMES Q 3. 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)] a) b) 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