Topic 3.2

Essential idea: Chromosomes carry genes in a linear sequence that is shared by members of a species.


3.2.U1 Prokaryotic have one chromosome consisting of a circular DNA molecule

Prokaryote chromosome

3.2.U2 Some prokaryotic also have plasmids but eukaryotes do not

Prokaryote chromosome

3.2.U3 Eukaryote chromosomes are linear DNA molecules associated with histone proteins

Place mouse pointer on Figure 2 to show how histones are wrapped by DNA molecule.

Trophic levels in a food web

3.2.U4 In a eukaryote species there are different chromosomes that carry different genes

Place mouse pointer on Figure for information on species and chromosomes.

Comparing chromosomes of humans, chimpanzees, gorillas and orangutans

3.2.U5 Homologous chromosomes carry the same sequence of genes but not necessarily the same alleles of those genes

homologous chromosomes

3.2.U6 Diploid nuclei have pairs of homologous chromosomes
             3.2.U7 Haploid nuclei have one chromosome of each pair

homologous chromosomes

3.2.U8 The number of chromosomes is a characteristic feature of members of a species

Table below shows the chromosome (diploid) number of different species.

Different species chromosome number

3.2.U9 A karyogram shows the chromosomes of an organism in homologous pairs of decreasing length

Decreasing length of chromosomes

3.2.U10 Sex is determined by sex chromosomes and autosomes are chromosomes that do not determine sex

Autosomes vs sex chromosomes


3.2.A1 Cairns' technique for measuring the length of DNA molecules by autoradiography

Cairns technique for measuring the length of DNA molecules

3.2.A2 Comparison of genome size in T-2 phages, Escherichia coli, Drosphila melanogaster, Homo Sapiens and Paris japonica

Comparing genome size of different species

3.2.A3 Comparison diploid chromosome numbers of Homo sapiens, Pan troglodytes, Canis familiaris, Oryza sativa                      and Parascaris equorum

Comparing diploid chromosome numbers of different species

3.2.A4 Use of karyogram to deduce sex and diagnose Down syandndrome in humans

Practice Karyotyping
Answer Key


3.2.S1 Use of databases to identify the locus of the human gene and its polypeptide product

Go to Bioinformatics Basics
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